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Journal Publications

This section contains all refereed journal publications that have some connection either with the Mace Head Research Station or with members, both present and past, of the Atmospheric Physics Research Cluster at NUI, Galway.

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Documents

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Proceedings of the Royal Irish Academy The Calibration of a photo-electric nucleus counter. Proceedings of the Royal Irish Academy The Calibration of a photo-electric nucleus counter.

Date added: 08/31/1946
Date modified: 07/22/2009
Filesize: 4.32 MB
P.J Nolan, L.W. Pollack, Proceedings of the Royal Irish Academy The Calibration of a photo-electric nucleus counter., Volume L1, Section A, No. 2, 1946

Abstract

 

Models of nucleus counterm designed to measure photo-electrically the decrease in intensity of a beam of light which has passed one or more times through an artificially produced fog, are described by L.W. Pollak and W.A. Morgan in a paper.

Statistical characteristics and predictability of particle formation events at Mace Head Statistical characteristics and predictability of particle formation events at Mace Head

Date added: 08/01/2006
Date modified: 07/23/2009
Filesize: 498.16 kB
Yoon, Y.J., C.D. O’Dowd, S.G. Jennings, S.H. Lee, Statistical characteristics and predictability of particle formation events at Mace Head, J. Geophys. Res.,doi:10.1029/2005JD006284, 2006.

Abstract


The seasonal characteristics of coastal nucleation events at the Mace Head Atmospheric Research Station, resulting from exposure of macroalgae to the atmosphere, were analyzed for a 2-year period from August 2002 to July 2004. Nucleation events occurred on 58% of the days over the period. The seasonal variation of the number of event days and event duration show a clear cycle, with maximum values in spring and autumn and the minimum values in the winter season. The nucleation events typically start ∼75 min prior to the occurrence of the low-tide mark and the event start time is correlated (r = 0.75) to the low-tide height. The intensity of the events, as determined by the peak particle concentrations achieved, is also positively correlated with the amount of tidal areas exposed to ambient air, as determined by the tidal height, and solar radiation. A nucleation potential index (NPI) was developed as a tool to provide a predictive capability for event prediction at Mace Head. The index was derived from normalized tidal height, solar radiation intensity, and wind direction and was compared with the occurrence of nucleation events from the database. The result shows that Mace Head particle formation events can be quite well predicted with a threshold probability of 50%.

The charging of water drops falling and colliding in an electric field The charging of water drops falling and colliding in an electric field

Date added: 01/01/1972
Date modified: 07/07/2009
Filesize: 1.67 MB

O'Connor, T.C. and Sharkey, W.P.F. (1960)- Ionization equilibrium in maritime air, Proc. Roy. Ir. Acad., 61, p.15-27.


Abstract


Studies have been made of the charge transfer resulting from the collision and separation of water drops falling in an electric field. The charge transferq was measured for values of field strengthE, impact velocityV, drop radiiR, r, radius ratioR/r, and angle THgr ranging from 0.5 to 80 kV/m, 0.5 to 3 m·sec–1, 200 to 600 mgr, 1.0 to 3.0 and 0 to 90 degrees respectively, where THgr is the angle between the field and the line of centres of the drops at the moment of separation.

Two uniformly sized drop-streams were ejected from hypodermic needles by modulating the flow of water through them and then collided between a pair of electrodes across which a potential difference existed. The drops coalesced temporarily, swung around each other and separated, each resulting stream being collected in a vessel connected to an electrometer in order to measure the charge. The measured values ofq were generally in good agreement with theoretical values derived from the equationq = 1.1 · 10-10 gamma1 E r 2 Cos THgr, where gamma1 is a function ofR/r.
Calculations based on this equation, the Marshall-Palmer drop-size distribution and established values of separation probabilities of colliding drops showed that collisions between raindrops within electrified clouds will act powerfully to dissipate the existing fields.

Condensation and coagulation sinks and formation of NMP in coastal and boreal forest BL Condensation and coagulation sinks and formation of NMP in coastal and boreal forest BL

Date added: 08/06/2002
Date modified: 07/21/2009
Filesize: 360.63 kB

Dal Maso, M., M. Kulmala, K. E. J. Lehtinen, J. M. Mäkelä, P. Aalto, and C. D. O'Dowd (2002), Condensation and coagulation sinks and formation of nucleation mode particles in coastal and boreal forest boundary layers, J. Geophys. Res., 107(D19), 8097, doi:10.1029/2001JD001053.


Abstract


The formation and growth of new particles has been evaluated using a revised version of a simple, but novel, theoretical tool. The concentration of condensable vapors and their source rates has been estimated using the aerosol condensation sink together with the measured particle growth rate. Also, by adding the coagulation sink and the measured formation rate of 3 nm particles, the formation rate of 1 nm particles and their concentration can be estimated. Condensation and coagulation sinks can be obtained from ambient aerosol size distribution data. The method has been applied to analyze the particle formation and growth rates observed during coastal and boreal forest nucleation events. The condensation sinks are typically 4-7 x 10-3 s-1 in the forest and 2 x 10-3 s-1 under coastal conditions, while the coagulation sinks for 1, 2, and 3 nm particles are typically smaller by factors 1.5-2, 5-7, and 11-15, respectively. The measured growth rates are 2-10 nm/h for the boreal forest and range from 15 to 180 nm/h at the coast, corresponding to a vapor concentration of 2-13 x 10 cm-3 and 108 cm-3 to 109 cm-3, respectively. The vapor source rate was 1-2 x 105 cm-3 s-1 in the boreal forest and 2-5 x 106 cm-3s-1 in the coastal environment. The estimated formation rate of 1 nm particles in the forest environment was 8-20 cm-3s-1 and 300-10,000 cm-3 s-1 at the coast. The concentration of 1 nm particles was estimated to be 2000-5000 and 4 × 104-7 × 106 particles cm-3 in forest and at coast, respectively.

 

An overview of current issues in the uptake of atmospheric trace gases by aerosols and clouds An overview of current issues in the uptake of atmospheric trace gases by aerosols and clouds

Date added: 11/10/2010
Date modified: 11/10/2010
Filesize: 1.06 MB

Kolb, C. E., R. A. Cox, J. P. D. Abbatt, M. Ammann, E. J. Davis, D. J. Donaldson, B. C. Garrett, C. George, P. T. Griffiths, D. R. Hanson, M. Kulmala, G. McFiggans, U. Pöschl, I. Riipinen, M. J. Rossi, Y. Rudich, P. E. Wagner, P. M. Winkler, D. R. Worsnop, and C. D. O' Dowd, An overview of current issues in the uptake of atmospheric trace gases by aerosols and clouds, Atmos. Chem. Phys.10, 10561–10605, doi:10.5194/acp-10-10561-2010, 2010.


A workshop was held in the framework of the ACCENT (Atmospheric Composition Change – a European Network) Joint Research Programme on “Aerosols” and the Programme on “Access to Laboratory Data”. The aim of the workshop was to hold “Gordon Conference” type discussion covering accommodation and reactive uptake of water vapour and trace pollutant gases on condensed phase atmospheric materials. The scope was to review and define the current state of knowledge of accommodation coefficients for water vapour on water droplet and ice surfaces, and uptake of trace gas species on a variety of different surfaces characteristic of the atmospheric condensed phase particulate matter and cloud droplets. Twenty-six scientists participated in this meeting through presentations, discussions and the development of a consensus review.  In this review we present an analysis of the state of knowledge on the thermal and mass accommodation coefficient for  water vapour on aqueous droplets and ice and a survey of current state-of the-art of reactive uptake of trace gases on a range of liquid and solid atmospheric droplets and particles. The review recommends consistent definitions of the various parameters that are needed for quantitative representation of the range of  as/condensed surface kinetic processes important for the atmosphere and identifies topics that require  additional research.

Isotope values of atmospheric halocarbons and hydrocarbons from Irish urban, rural, and marine Isotope values of atmospheric halocarbons and hydrocarbons from Irish urban, rural, and marine

Date added: 08/06/2007
Date modified: 07/24/2009
Filesize: 750 kB

Redeker, K. R., S. Davis, and R. M. Kalin (2007), Isotope values of atmospheric halocarbons and hydrocarbons from Irish urban, rural, and marine locations, J. Geophys. Res., 112, D16307, doi:10.1029/2006JD007784.


Abstract

 

Stable carbon isotope ratios for 37 hydrocarbon, CFC and halocarbon compounds were determined over the course of 1 year (86 samples) from the urban Belfast environment, Northern Ireland (NI). A smaller number of samples were collected from rural locations at Crossgar and Hillsborough, NI, and one marine location at Mace Head, Republic of Ireland. Source δ 13C “signatures” suggest that <C5 alkanes are most likely derived from natural gas and liquid petroleum gas while >C5 alkanes and ≥C4 alkenes are most likely derived from vehicle emissions. C3–C5 hydrocarbons show significant enrichment of δ 13C with iso-alkanes < n-alkanes < alkenes < alkynes. There is also significant enrichment of δ 13C from propane to n-butane to n-pentane. There is no significant separation between n-pentane, n-hexane, n-heptane or methyl-butane, methyl pentane and methyl hexanes. Calculated hydroxyl reaction kinetic isotope effects and subsequent δ 13C enrichment are insufficient to explain shifts in isotopic ratio relative to concentration for all compounds as is differences in origin of air mass. Very few compounds show significant diurnal shifts; however, alkanes and ≥C4 alkenes demonstrate consistent enrichment of isotopic ratios when summer samples are compared to winter samples. Benzene is the sole compound measured that appears to become more depleted in δ 13C when summer samples are compared against winter samples. Urban air, sampled at Belfast, which has originated in Europe shows enriched values for hydrocarbons while air which has originated in the Arctic Ocean is most similar to marine air off the Atlantic, sampled at Mace Head, Ireland.

 

Decreasing trends in total gaseous mercury observations in baseline air at Mace Head, Ireland from 1 Decreasing trends in total gaseous mercury observations in baseline air at Mace Head, Ireland from 1

Date added: 05/25/2011
Date modified: 05/25/2011
Filesize: 649.24 kB

R. Ebinghaus, S.G. Jennings, H.H. Kock , R.G. Derwent , A.J. Manning , and T.G. Spain,  Decreasing trends in total gaseous mercury observations in baseline air at Mace

Head, Ireland from 1996 to 2009, Atmos. Environ., doi:10.1016/j.atmosenv.2011.01.033


In this study, the concentrations of total gaseous mercury in baseline air masses arriving at Mace Head, Ireland after having traversed the thousands of kilometres uninterrupted fetch of the North Atlantic Ocean, have been used for the assessment of possible trends in the atmospheric mercury background concentration over a 14-year period (i.e., 1996 -2009), a statistically significant negative (downwards) trend of -0.028 ±0.01 ng m-3 yr-1, representing a trend of 1.6 - 2.0% per year, has been detected in the total gaseous mercury levels in these baseline air masses. These findings are set in the context of the available literature studies of atmospheric Hg trends.

Chemical and physical characteristics of aerosol particles at a remote coastal location, Mace Head, Ireland, during NAMBLEX Chemical and physical characteristics of aerosol particles at a remote coastal location, Mace Head, Ireland, during NAMBLEX

Date added: 08/01/2005
Date modified: 07/01/2009
Filesize: 435.58 kB

Coe, H., J. D. Allan, R. M. Alfarra, K. N. Bower, M. J. Flynn, G. B. McFiggans, D. O. Topping, P. I. Williams, C. D. O'Dowd, M. Dall'Osto, D. C. S. Beddows and R. M. Harrison, Chemical and physical characteristics of aerosol particles at a remote coastal location, Mace Head, Ireland, during NAMBLEX, Atmospheric Chemistry and Physics Discussions, Vol. 5, pp 11643-11678, 2005.


Abstract


Aerosol number concentrations and size distributions from 3 nm to 20 µm diameter were measured at the Mace Head Atmospheric Research Station, Co. Galway, Ireland, a coastal site on the eastern seaboard of the north Atlantic Ocean. Both on and offline size resolved aerosol composition measurements were also made using an Aerodyne Aerosol Mass Spectrometer (AMS) and ion chromatographic analysis of daily samples collected using a Micro-Orifice Uniform Deposit Impactor (MOUDI). Particle number concentrations, size distributions and AMS measurements were determined at 7 and 22 m above ground level to investigate local effects on the aerosol size distribution induced by the tidal zone. During periods of new particle formation ultrafine particle number concentrations are large and variable, however, outside these periods no variability in particle number was observed at any size, nor was the particle composition variable. Analysis of particle size distributions show that within each air mass observed particle number concentrations were very consistent. During anticyclonic periods and conditions of continental outflow Aitken and accumulation mode were enhanced by a factor of 5 compared to the marine sector, whilst coarse mode particles were enhanced during westerly conditions. Baseline marine conditions were rarely met at Mace Head during NAMBLEX and high wind speeds were observed for brief periods only.

Loss rates of gaseous species to aerosol surfaces were calculated for a range of uptake coefficients. Even when the accommodation coefficient is unity, lifetimes of less than 100 s were never observed and rarely were lifetimes less than 500 s. Diffusional limitation to mass transfer is important in most conditions as the coarse mode is always significant, we calculate a minimum overestimate of 50% in the loss rate if this is neglected and so it should always be considered when calculating loss rates of gaseous species to particle surfaces. HO2 and HOI have accommodation coefficients of around 0.03 and hence we calculate lifetimes due to loss to particle surfaces of 2000 s or greater. Aerosol composition measurements using the AMS show accumulation mass modes of acidified sulphate and organic material, both of which have the same shape and are centred at around 350 nm vacuum aerodynamic diameter, implying an internal mixture. The organic and sulphate are approximately equally important, though the mass ratio varies considerably between air masses. Mass spectral fingerprints of the organic fraction in polluted conditions are similar to those observed at other locations that are characterised by aged continental aerosol. Even in marine conditions a background concentration of between 0.5 and 1 µg m−3 of both organic and sulphate was observed. Key differences in the mass spectra were observed during the few clean periods but were insufficient to ascertain whether these changes reflect differences in the source fingerprint of the organic aerosol. However, in an accompanying paper (Dall'Osto et al., 2005) periods of organic dominated aerosol particles were also observed and could be separated from the aged continental aerosol. The coarse mode was composed of sea salt and showed significant displacement of chloride by nitrate and to a lesser extent sulphate in polluted conditions.

Role of organic and black carbon in the chemical composition of atmospheric aerosol at European background sites Role of organic and black carbon in the chemical composition of atmospheric aerosol at European background sites

Date added: 08/01/2001
Date modified: 07/23/2009
Filesize: 205.08 kB

Krivacsy, Z., Hoffer, A., Sarvari, Zs., Temesi, D., Baltensperger, U., Nyeki, S., Weingartner, E., Kleefeld, S., Jennings, S.G., 2001. Role of organic and black carbon in the chemical composition of atmospheric ,aerosol at European background sites. Atmospheric Environment 35, 6231-6244.


Abstract


The mass concentrations of inorganic ions, water-soluble organic carbon, water-insoluble organic carbon and black carbon were determined in atmospheric aerosol collected at three European background sites: (1) the Jungfraujoch, Switzerland (high-alpine, PM2.5 aerosol); (2) K-puszta, Hungary (rural, PM1.0 aerosol); (3) Mace Head, Ireland (marine, total particulate matter). At the Jungfraujoch and K-puszta the contribution of carbonaceous compounds to the aerosol mass was higher than that of inorganic ions by 33% and 94%, respectively. At these continental sites about 60% of the organic carbon was water soluble, 55-75% of the total carbon proved to be refractory and a considerable portion of the water soluble, refractory organic matter was composed of humic-like substances. At Mace Head the mass concentration of organic matter was found to be about twice than that of nonsea-salt ions 40% of the organic carbon was water soluble and the amount of highly refractory carbon was low. Humic-like substances were not detected but instead low molecular weight carboxylic acids were responsible for about one-fifth of the water-soluble organic mass. These results imply that the influence of carbonaceous compounds on aerosol properties (e.g. hygroscopic, optical) might be significant.

Modelling OH, HO2, and RO2 radicals in the marine boundary layer 2. Mechanism reduction and unce Modelling OH, HO2, and RO2 radicals in the marine boundary layer 2. Mechanism reduction and unce

Date added: 08/06/1999
Date modified: 07/23/2009
Filesize: 1.21 MB

Carslaw N., P.J. Jacobs, and M.J. Pilling (1999), Modelling OH, HO2 and RO2 radicals in the marine boundary layer: 2. Mechanism reduction and uncertainty analysis, J. Geophys. Res., 104, 30257-30273.


Abstract


An observationally constrained box model has been constructed to investigate radical chemistry at the Mace Head Atmospheric Observatory, a remote marine location on the west coast of Ireland. The primary aim of the model has been to model concentrations of the hydroxyl (OH), hydroperoxy (HO2), and the sum of peroxy Σ([HO2]+[RO2]) radicals measured by in situ instruments at this location. The model used in these studies consists of about 1670 reactions and 500 species, and model predictions of radical concentrations have been evaluated against field data. In order to further understand the chemistry, the model has been reduced using sensitivity analysis on both a clean and a semipolluted day. For reduced mechanisms that predict the concentrations of OH and HO2 to within 5% of the full mechanism, the semipolluted day can be represented using 279 species and 986 reactions, and the clean day using 249 species and 894 reactions. A further reduction has been applied whereby the reduced mechanisms predict concentrations of OH and HO2 to within 20% of the full mechanism for the daytime hours. In this way, the OH and HO2 concentrations on the semipolluted day can be represented by 42 species and 64 reactions, and the clean day by 17 species and 25 reactions. We show that these reduced mechanisms are generally applicable for this location under broadly similar conditions. Simple steady state expressions have also been derived to represent the chemistry at this location, allowing the concentrations of OH and HO2 to be deduced analytically. The expressions are based on the reduced mechanisms and on a further analysis of the reaction rates. Finally, an uncertainty analysis has been carried out to quantify the effects of propagation of uncertainties in the rate parameters and constrained concentrations through to the calculated radical concentrations in the model. For model concentrations of OH, HO2, and Σ([HO2]+[RO2]) radicals, the 2σ uncertainties are 31, 21, and 25%, respectively for clean air, and 42, 25, and 27% for semipolluted air.

 

A study of peroxy radicals and ozone photochemistry at coastal sites in the northern and southe A study of peroxy radicals and ozone photochemistry at coastal sites in the northern and southe

Date added: 08/06/1997
Date modified: 07/27/2009
Filesize: 1.01 MB

Carpenter, L. J., P. S. Monks, B. J. Bandy, S. A. Penkett, I. E. Galbally, and C. P. (. Meyer (1997), A study of peroxy radicals and ozone photochemistry at coastal sites in the northern and southern hemispheres, J. Geophys. Res., 102(D21), 25,417–25,427.


Abstract


Peroxy radicals and other important species relevant to ozone photochemistry, including ozone, its photolysis rate coefficient jO(1 D), NOx (NO + NO2), and peroxides, were measured at the coastal sites of Cape Grim, Tasmania, in January/February 1995 during the Southern Ocean Atmospheric Photochemistry Experiment (SOAPEX 1) and Mace Head, Western Ireland, in May 1995 during the Atlantic Atmospheric Photochemistry Experiment (ATAPEX 1). At both sites it was observed that the relationship between peroxy radical (HO2 + RO2) concentrations and jO(1 D) switched from a square root dependence in clean oceanic or “baseline” air to a first-order dependence in more polluted air. Simple algorithms derived from a photochemical reaction scheme indicate that this switch-over occurs when atmospheric NO levels are sufficient for peroxy radical reaction with NO to compete with radical recombination reactions. At this crucial point, net tropospheric ozone production is expected to occur and was observed in the ozone diurnal cycles when the peroxy radical/jO(1 D) dependencies became first order. The peroxy radical/jO(1 D) relationships imply that ozone production exceeds destruction at NO levels of 55±30 parts per trillion by volume (pptv) at Mace Head during late spring and 23±20 pptv at Cape Grim during summer, suggesting that the tropospheric ozone production potential of the southern hemisphere is more responsive to the availability of NO than that of the northern hemisphere.

 

Effects of source temporal resolution on transport simulations of boreal fire emissions Effects of source temporal resolution on transport simulations of boreal fire emissions

Date added: 08/06/2006
Date modified: 07/27/2009
Filesize: 427.81 kB

Hyer, E. J., E. S. Kasischke, and D. J. Allen (2007), Effects of source temporal resolution on transport simulations of boreal fire emissions, J. Geophys. Res., 112, D01302, doi:10.1029/2006JD007234.


Abstract


The quality of temporal information from daily burned area inputs was evaluated using a transport and chemistry experiment. Carbon monoxide emissions from boreal forest fires were estimated using burned area inputs with daily resolution. Averaging of emissions data to create 30-day aggregate data reduced the variance by 80%, indicating a substantial loss of information. Data from Russia, Canada, and Alaska were tested for periodicity to uncover systematic gaps in daily data. Some evidence of periodicity was found in data from Alaska, where temporal information came from fire mapping by the Alaskan Fire Service. Autocorrelation decayed rapidly and nearly monotonically for Canada and Russia, where temporal information came from Advanced Very High Resolution Radiometer (AVHRR) satellite observations. Daily data as well as 7-day and 30-day aggregates were used as input to the University of Maryland Atmospheric Chemistry and Transport Model, and output was compared with CO observations from the Cooperative Air Sampling Network (CASN); continuous measurements from Mace Head, Ireland; and total column CO retrievals from the Measurement of Pollution in the Troposphere (MOPITT) instrument. CASN flask measurements showed no sensitivity to high-frequency variability in the source, indicating the effectiveness of the filtering protocol at ensuring only well-mixed air masses are sampled in this data set. Differences between daily and 7-day simulations were too small for quantitative comparison in any of the data. For cases where the differences were substantial, simulations using daily and 7-day average sources agreed better with observations than 30-day average sources.

 

Measurement of OH and HO2 in the Troposphere Measurement of OH and HO2 in the Troposphere

Date added: 08/06/2003
Date modified: 07/23/2009
Filesize: 669.08 kB

D. E. Heard and M. J. Pilling, "Measurement of OH and HO2 in the troposphere," Chem. Rev. 103, 5163-5198 (2003).


Abstract


Volatile organic compounds (VOCs), emitted into the atmosphere, react with a range of oxidants, of which the most important are OH, NO3, and ozone. Under most atmospheric conditions, and during the day, the removal of VOCs is dominated by their reaction with OH. This ability of the atmosphere to “cleanse itself”, and to continue doing so into the future, affects many processes. The concentration of methane, and hence its contribution to radiative forcing, is determined by the balance between its rate of emission and the rate of its removal by reaction with OH. The global distribution and seasonal variability of methane depend on the interaction between emission and reaction with OH. Tropospheric oxidation is also responsible for the formation of groundlevel ozone and photochemical smog and for the production of secondary organic aerosols. The spatial distribution and concentrations of oxidants, such as OH, depend on a wide range of factors, including emissions of both volatile organic compounds and nitrogen ooxides and the interaction of atmospheric transport and chemical kinetics. Oxidation is a complex chemical process, which proceeds through a series of partially oxidized intermediates; the primary emitted compounds and the intermediates have a wide range of atmospheric lifetimes, from minutes to years, depending, in most cases, on their rate constants for reaction with OH and the OH  concentration, [OH]. Thus, the concentrations of photochemically active radical precursors, such as acetone in the upper troposphere, depend on their formation by oxidation of VOCs emitted at the surface, their atmospheric lifetimes, and their rate of vertical transport. Clearly, OH plays a central role in tropospheric chemistry. The in situ measurement of its concentration has long been a goal, but its short lifetime and consequently low concentration provide a seriouschallenge. Considerable progress has been made, however, over the last 10 years, and there are now several OH instruments which are actively used for both ground- based and aircraft-based campaigns, employing principally laser-induced fluorescence, laser absorption, and chemical ionization. Some of these instruments can also be used to measure HO2, which is closely coupled to OH; [OH]:[HO2] depends sensitively on the chemical composition of the atmosphere and particularly on the concentrations of VOCs and NOx. The atmospheric lifetime of OH is 1 s or less, and it has been argued that its concentration is determined only by the local concentrations of longer-lived species such as O3, VOCs, and NOx, and is not affected directly by atmospheric transport. Thus, field measurements of [OH] can be interpreted through zero-dimensional chemical box models, in which the concentrations of longer-lived species are constrained to simultaneous, co-located measured values. This approach has led to the use of measurements of [OH], coupled with contemporaneous measurements of other species, as a way of evaluating chemical mechanisms for atmospheric oxidation. The interpretation of the box models has also provided a means of investigating the interaction of component reactions in the chemical mechanisms under a range of differing but representative chemical environments.

(NAMBLEX). Overview of the campaign held at Mace Head,  Ireland, in summer 2002 (NAMBLEX). Overview of the campaign held at Mace Head, Ireland, in summer 2002

Date added: 08/06/2006
Date modified: 07/27/2009
Filesize: 9.65 MB

Heard, D. E., Read, K. A., Methven, J., Al-Haider, S., Bloss, W. J., Johnson, G. P., Pilling, M. J., Seakins, P. W., Smith, S. C., Sommariva, R., Stanton, J. C., Still, T. J., Ingham, T., Brooks, B., De Leeuw, G., Jackson, A. V., McQuaid, J. B., Morgan, R., Smith, M. H., Carpenter, L. J., Carslaw, N., Hamilton, J., Hopkins, J. R., Lee, J. D., Lewis, A. C., Purvis, R. M., Wevill, D. J., Brough, N., Green, T., Mills, G., Penkett, S. A., Plane, J. M. C., Saiz-Lopez, A., Worton, D., Monks, P. S., Fleming, Z., Rickard, A. R., Alfarra, M. R., Allan, J. D., Bower, K., Coe, H., Cubison, M., Flynn, M., McFiggans, G., Gallagher, M., Norton, E. G., O'Dowd, C. D., Shillito, J., Topping, D., Vaughan, G., Williams, P., Bitter, M., Ball, S. M., Jones, R. L., Povey, I. M., O'Doherty, S., Simmonds, P. G., Allen, A., Kinnersley, R. P., Beddows, D. C. S., Dall'Osto, M., Harrison, R. M., Donovan, R. J., Heal, M. R., Jennings, S. G., Noone, C., and Spain, G.: The North Atlantic Marine Boundary Layer Experiment(NAMBLEX). Overview of the campaign held at Mace Head, Ireland, in summer 2002, Atmos. Chem. Phys., 6, 2241-2272, 2006.


Abstract


The North Atlantic Marine Boundary Layer Experiment (NAMBLEX), involving over 50 scientists from 12 institutions, took place at Mace Head, Ireland (53.32° N, 9.90° W), between 23 July and 4 September 2002. A wide range of state-of-the-art instrumentation enabled detailed measurements of the boundary layer structure and atmospheric composition in the gas and aerosol phase to be made, providing one of the most comprehensive in situ studies of the marine boundary layer to date. This overview paper describes the aims of the NAMBLEX project in the context of previous field campaigns in the Marine Boundary Layer (MBL), the overall layout of the site, a summary of the instrumentation deployed, the temporal coverage of the measurement data, and the numerical models used to interpret the field data. Measurements of some trace species were made for the first time during the campaign, which was characterised by predominantly clean air of marine origin, but more polluted air with higher levels of NOx originating from continental regions was also experienced. This paper provides a summary of the meteorological measurements and Planetary Boundary Layer (PBL) structure measurements, presents time series of some of the longer-lived trace species (O3, CO, H2, DMS, CH4, NMHC, NOx, NOy, PAN) and summarises measurements of other species that are described in more detail in other papers within this special issue, namely oxygenated VOCs, HCHO, peroxides, organo-halogenated species, a range of shorter lived halogen species (I2, OIO, IO, BrO), NO3 radicals, photolysis frequencies, the free radicals OH, HO2 and (HO2+Σ RO2), as well as a summary of the aerosol measurements. NAMBLEX was supported by measurements made in the vicinity of Mace Head using the NERC Dornier-228 aircraft. Using ECMWF wind-fields, calculations were made of the air-mass trajectories arriving at Mace Head during NAMBLEX, and were analysed together with both meteorological and trace-gas measurements. In this paper a chemical climatology for the duration of the campaign is presented to interpret the distribution of air-mass origins and emission sources, and to provide a convenient framework of air-mass classification that is used by other papers in this issue for the interpretation of observed variability in levels of trace gases and aerosols.

Production Flux of Sea-Spray Aerosol. Rev. of Geophys., Production Flux of Sea-Spray Aerosol. Rev. of Geophys.,

Date added: 05/12/2011
Date modified: 05/12/2011
Filesize: 2.68 MB

de Leeuw, G., E. Andreas, M. Anguelova , C. Fairall , E. Lewis , C. O'Dowd , M. Schulz , S. Schwartz , Production Flux of Sea-Spray Aerosol. Rev. of Geophys., doi:10.1029/2010RG000349, 2011


 

Knowledge of the sizeand compositiondependent production flux of primary sea spray aerosol (SSA) particles and its dependence on environmental variables is required for modeling cloud microphysical properties and aerosol radiative influences, interpreting measurements of particulate matter in coastal areas and its relation to air quality, and evaluating rates of uptake and reactions of gases in sea spray drops. This review examines recent research pertinent to SSA production flux, which deals mainly with production of particles with r80 (equilibrium radius at 80% relative humidity) less than 1 mm and as small as 0.01 mm. Production of sea spray particles and its dependence on controlling factors has been investigated in aboratory studies that have examined the dependences on water temperature, salinity, and the presence of organics and in field measurements with micrometeorological techniques that use newly developed fast optical particle sizers. Extensive measurements show that waterinsoluble organic matter contributes substantially to the omposition of SSA particles with r80 < 0.25 mm and, in locations with high biological activity, can be the ominant constituent. Orderofmagnitude variation  remains in estimates of the sizedependent production flux per white area, the quantity central to formulations of the production flux based on the whitecap method. This variation indicates that the production flux may depend on quantities such as the volume flux of air bubbles to the surfacet hat are not accounted for in current models. Variation in estimates of the whitecap fraction as a function of wind speed contributes additional, comparable uncertainty to production flux estimates.  

Long-term changes in tropospheric ozone Long-term changes in tropospheric ozone

Date added: 08/07/2006
Date modified: 07/24/2009
Filesize: 849.93 kB

Oltmans, S. J., et al. (2006), Long-term changes in tropospheric ozone, Atmos. Environ.,
40, 3156-3173


Abstract

In this review we attempt to critically evaluate the availability of reliable tropospheric ozone measurements suitable for long-term trend analysis. The focus is on large-scale changes deduced from measurements, which are used for comparison with numerical simulations of the tropospheric ozone cycle. These are required to quantify the influence of anthropogenic ozone precursor emission changes on climate. Long-term tropospheric ozone measurements show that ozone over Europe has increased by more than a factor of two between World War II and the early 1990s which is consistent with the large increase in anthropogenic ozone precursor emissions in the industrialized world. However, the further increase in background ozone over Europe and North America since the early 1990s cannot be solely explained by regional ozone precursor changes because anthropogenic ozone precursor emissions decreased in the industrialized countries as consequence of air pollution legislation. Measurements also indicate large increases in ozone in the planetary boundary layer over the tropical Atlantic since the late 1970s, which have been attributed to large increases in fossil fuel related emissions. Measurements at southern midlatitudes, which are limited in number, show a moderate increase in tropospheric ozone since the middle of the 1990s.

 

Aerosol Climatology Measurements with a Nolan-Pollack Counter.. Aerosol Climatology Measurements with a Nolan-Pollack Counter..

Date added: 07/31/1991
Date modified: 07/27/2009
Filesize: 1.24 MB

O'Connor, T.C & McGovern, F.M. (1991)- Aerosol climatology measurements with a Nolan-Pollak counter. Atmospheric Environment, 25A, pp. 563-567.


Abstract


The Nolan-Pollak photoelectic Nucleus Counter was originally developed in the 1940s for aerosol climatology measurements although its versatility led subsequently to many other applications in aerosol science. It has been widely used in manuel, automatic and modified forms in many parts of the world to record ambient concentrations of Aitken nuclei. The design calibrations and performance of an automatic counter is described. Measurements of Aikten nuclei at MAce HEad, Ireland, are used to discuss it's sustainablity for the prpose of aerosol climatology.

 

Charge separation due to water drop and cloud droplet interactions in an electric field Charge separation due to water drop and cloud droplet interactions in an electric field

Date added: 01/01/1975
Date modified: 07/01/2009
Filesize: 2.09 MB
Jennings, S.G. (1975)- Charge separation due to water drop and cloud droplet interactions in an electric field. Quart. J. Roy. Met. Soc., 101, 227-233.   
Abstract

Measurements were made of the electric charge acquired by drops of mean radius of about 750m, in the presence of a vertical electric field E, the value of which could be varied from 4·5 to 27kV/m. It was found that the average charge acquired by the water drop as a consequence of the inductive process increased from 0·1fC to about 0·25fC as the electric field strength increased from 5kV/m to about 15kV/m, but there-after decreased with increasing values of electric field.
This work suggests that the collisions between polarized rain-drops and cloud droplets in natural clouds could give rise, very effectively, to the production of electric fields of about 30kV/m; but that significantly larger fields could not be produced since all collisions in the higher fields would result in permanent coalescence.

Regional model simulation of North Atlantic cyclones...response to increased sea surface temper Regional model simulation of North Atlantic cyclones...response to increased sea surface temper

Date added: 08/06/2007
Date modified: 07/06/2009
Filesize: 2.79 MB

Semmler, T., S. Varghese, R. McGrath, P. Nolan, S. Wang, P. Lynch, and C. O'Dowd (2008), Regional model simulation of North Atlantic cyclones: Present climate and idealized response to increased sea surface temperature, J. Geophys. Res., 113, D02107, doi:10.1029/2006JD008213.


Abstract


The influence of an increased sea surface temperature (SST) on the frequency and intensity of cyclones over the North Atlantic is investigated using two data sets from simulations with the Rossby Centre regional climate model RCA3. The model domain comprises large parts of the North Atlantic and the adjacent continents. RCA3 is driven by reanalysis data for May to December 1985–2000 at the lateral and lower boundaries, using SST and lateral boundary temperatures. A realistic interannual variation in tropical storm and hurricane counts is simulated. In an idealized sensitivity experiment, SSTs and boundary condition temperatures at all levels are increased by 1 K to ensure that we can distinguish the SST from other factors influencing the development of cyclones. An increase in the count of strong hurricanes is simulated. There is not much change in the location of hurricanes. Generally weaker changes are seen in the extratropical region and for the less extreme events. Increases of 9% in the count of extratropical cyclones and 39% in the count of tropical cyclones with wind speeds of at least 18 m/s are found.

 

Organic matter contribution to marine aerosols and cloud condensation nuclei Organic matter contribution to marine aerosols and cloud condensation nuclei

Date added: 09/23/2008
Date modified: 07/23/2009
Filesize: 158.68 kB

Baerbel Langmann, Claire Scannell, Colin O'Dowd, New Directions: Organic matter contribution to marine aerosols and cloud condensation nuclei, Atmospheric Environment, Volume 42, Issue 33, October 2008, Pages 7821-7822, ISSN 1352-2310, DOI: 10.1016/j.atmosenv.2008.09.002.


Abstract

 

Aerosols in the marine atmosphere influence solar irradiation over the world's ocean directly by backscattering incoming solar radiation and indirectly, by forming cloud condensation nuclei (CCN) thereby affecting the cloud albedo. Charlson et al. (1987) suggested the existence of a feedback mechanism between climate change and the flux of oceanic dimethyl sulfide (DMS), commonly known as the CLAW hypothesis after the four founding authors. According to this hypothesis, DMS produced by marine phytoplankton is ventilated into the marine boundary layer (MBL) and ultimately oxidised to sulfate aerosol which form CCNs.

The change in cloud albedo results in a global temperature perturbation affecting the productivity of the marine biosphere and hence the concentration of oceanic DMS. The authors assumed that non-sea salt (nss) sulfate aerosol as oxidation product of DMS is the major source of CCN over the oceans thereby disregarding the potential of other chemical components of the submicron marine aerosol like sea salt and water soluble and water insoluble organic carbon (OC) to form CCNs. Since the publication of the CLAW hypothesis it has been difficult to prove or disprove the idea, however several studies (e.g. Woodhouse et al., 2008) have elucidated that DMS flux in the MBL alone cannot explain new particle and CCN formation.

In recent years, the role of natural organic aerosol in the marine environment has received increasing attention. Measurements indicate that the increase of the marine biological activity is accompanied by a considerable increase of the contribution of OC to the submicron marine aerosol (e.g. O'Dowd et al., 2004) exceeding the mass fraction of nss sulfate by a factor of more than two. OC aerosols are partly primary aerosols (POC) which are directly released from the ocean and partly secondary aerosols (SOC) which form in the atmosphere through chemical reactions of reactive gases released at the ocean surface. CCNs formed from POC and reactive gases like isoprene should be available much closer to areas with increased marine biological activity than CCNs formed from nss sulfate. Meskhidze and Nenes (2006) argued that SOC aerosols can act as efficient CCNs in the Southern Ocean, even though the authors had to revise their estimates of oceanic isoprene fluxes. Roelofs (2008) showed in a global model study that OC aerosols significantly contribute to marine cloud optical properties and seasonality by estimating a global annual flux of marine organic matter of about 75 Tg C yr−1 (corresponding to 90–135 Tg OC yr−1 depending on the applied conversion factor) whereas Spracklen et al. (2008) provide a global annual oceanic OC emission estimate of around 8 Tg OC yr−1. The very different approaches used by the authors lead to a one order of magnitude difference in the marine OC emissions estimates. As measurements are generally limited spatially and temporally and are only available for selected gases or aerosols, globally, the role of the ocean as a source of photochemical active gases and aerosols remains unclear.

We would like to contribute to an improved understanding of marine OC emissions by presenting a global annual marine OC flux estimate based on a different approach. A combined organic–inorganic submicron sea–spray source function (O'Dowd et al., 2008) is applied globally, where we make use of chlorophyll-a concentration obtained from MODIS Aqua and Terra satellite and wind speed obtained from SeaWinds on QuikSCAT as monthly average input information. The only difference to O'Dowd et al. (2008) is the use of a revised relationship between organic mass and chlorophyll concentration in the current estimate (organic mass [%] = 49.129 × chlorophyll [mg m−3]) because of recent corrections of the chemical analysis. The resulting marine flux of submicron OC aerosols is 2.3 Tg OC yr−1 for 2003 and 2.8 Tg C yr−1 for 2006, with a spatial distribution as shown in Fig. 1. As the submicron OC aerosols are likely internally mixed with sea-salt and therefore are already hygroscopic, they can act as sites for biogenic SOC condensation making them more active as CCN. Estimates for the very high latitudes should be regarded with caution because the satellite sensors have a large margin of errors in these regions. Our estimate of the global annual marine OC flux is in the range of that published by Spracklen et al. (2008), but approximately a factor of 3 lower as only submicron particles are considered here. The global distribution of the marine OC flux by Spracklen et al. (2008) follows the global distribution of chlorophyll-a, whereas high wind speed in the approach presented here leads to increased marine OC emissions in particular in the region of the Antarctic circumpolar current, the North Atlantic and the North Pacific Ocean and considerably lower emissions in the tropics and subtropics where wind speed is generally lower. Further measurements preferably in remote oceanic regions, and measurements and modelling studies on the mechanisms of marine OC production are needed to illuminate the nature and role of marine OC aerosols and their potential to act as CCNs.

A Combined Organic-Inorganic sea-spray Source Function A Combined Organic-Inorganic sea-spray Source Function

Date added: 08/06/2007
Date modified: 07/27/2009
Filesize: 317.72 kB

O'Dowd, C. D., B. Langmann, S. Varghese, C. Scannell, D. Ceburnis, and M. C. Facchini (2008), A combined organic-inorganic sea-spray source function, Geophys. Res. Lett., 35, L01801, doi:10.1029/2007GL030331.


Abstract


This study presents a novel approach to develop a combined organic-inorganic sub-micron sea-spray source function for inclusion in large-scale models. It requires wind speed and surface ocean chlorophyll-a concentration as input parameters. The combined organic-inorganic source function is implemented in the REMOTE regional climate model and sea-spray fields are predicted with particular focus on the North East Atlantic. The model predictions using the new source functions compare well with observations of total sea-spray mass and organic carbon fraction in sea-spray aerosol. During winter (periods of low oceanic biological activity), sea-salt dominates the sea-spray mass while in summer (when biological activity is high), water soluble organic carbon contributes between 60–90% of the submicron sea-spray mass.

 

Aerosol direct radiative effects over the northwest Atlantic, northwest Pacific, and North Indian Oc Aerosol direct radiative effects over the northwest Atlantic, northwest Pacific, and North Indian Oc

Date added: 08/01/2006
Date modified: 07/10/2009
Filesize: 2.78 MB

Bates, T. S. , T. L. Anderson, T. Baynard, T. Bond, O. Boucher, G. Carmichael, A. Clarke, C. Erlick, H. Guo, L. Horowitz, S. Howell, S. Kulkarni, H. Maring, A. McComiskey, A. Middlebrook, K. Noone, C. D. O'Dowd, J. Ogren, J. Penner, P. K. Quinn, A. R. Ravishankara, D. L. Savoie, S. E. Schwartz, Y. Shinozuka, Y. Tang, R. J. Weber and Y. Wu, Aerosol direct radiative effects over the northwest Atlantic, northwest Pacific, and North Indian Oceans: estimates based on in-situ chemical and optical measurements and chemical transport modelling, Atmospheric Chemistry and Physics Discussions, Vol. 6, pp 175-362, 2006.


Abstract


The largest uncertainty in the radiative forcing of climate change over the industrial era is that due to aerosols, a substantial fraction of which is the uncertainty associated with scattering and absorption of shortwave (solar) radiation by anthropogenic aerosols in cloud-free conditions (IPCC, 2001). Quantifying and reducing the uncertainty in aerosol influences on climate is critical to understanding climate change over the industrial period and to improving predictions of future climate change for assumed emission scenarios. Measurements of aerosol properties during major field campaigns in several regions of the globe during the past decade are contributing to an enhanced understanding of atmospheric aerosols and their effects on light scattering and climate. The present study, which focuses on three regions downwind of major urban/population centers (North Indian Ocean (NIO) during INDOEX, the Northwest Pacific Ocean (NWP) during ACE-Asia, and the Northwest Atlantic Ocean (NWA) during ICARTT), incorporates understanding gained from field observations of aerosol distributions and properties into calculations of perturbations in radiative fluxes due to these aerosols. This study evaluates the current state of observations and of two chemical transport models (STEM and MOZART). Measurements of burdens, extinction optical depth (AOD), and direct radiative effect of aerosols (DRE – change in radiative flux due to total aerosols) are used as measurement-model check points to assess uncertainties. In-situ measured and remotely sensed aerosol properties for each region (mixing state, mass scattering efficiency, single scattering albedo, and angular scattering properties and their dependences on relative humidity) are used as input parameters to two radiative transfer models (GFDL and University of Michigan) to constrain estimates of aerosol radiative effects, with uncertainties in each step propagated through the analysis. Constraining the radiative transfer calculations by observational inputs increases the clear-sky, 24-h averaged AOD (34±8%), top of atmosphere (TOA) DRE (32±12%), and TOA direct climate forcing of aerosols (DCF – change in radiative flux due to anthropogenic aerosols) (37±7%) relative to values obtained with "a priori" parameterizations of aerosol loadings and properties (GFDL RTM). The resulting constrained clear-sky TOA DCF is −3.3±0.47, −14±2.6, −6.4±2.1 Wm−2 for the NIO, NWP, and NWA, respectively. With the use of constrained quantities (extensive and intensive parameters) the calculated uncertainty in DCF was 25% less than the "structural uncertainties" used in the IPCC-2001 global estimates of direct aerosol climate forcing. Such comparisons with observations and resultant reductions in uncertainties are essential for improving and developing confidence in climate model calculations incorporating aerosol forcing.

Strong correlation between levels of tropospheric OH and UV-B Strong correlation between levels of tropospheric OH and UV-B

Date added: 04/22/2006
Date modified: 07/27/2009
Filesize: 1.22 MB

Rohrer, F. and H. Berresheim, Strong correlation between levels of tropospheric hydroxyl radicals and solar ultraviolet radiation, Nature, 442, 184-187, 2006.


Abstract


The most important chemical cleaning agent of the atmosphere is the hydroxyl radical, OH. It determines the oxidizing power of the atmosphere, and thereby controls the removal of nearly all gaseous atmospheric pollutants. The atmospheric supply of OH is limited, however, and could be overcome by consumption due to increasing pollution and climate change, with detrimental feedback effects. To date, the high variability of OH concentrations has prevented the use of local observations to monitor possible trends in the concentration of this species. Here we present and analyse long-term measurements of atmospheric OH concentrations, which were taken between 1999 and 2003 at the Meteorological Observatory Hohenpeissenberg in southern Germany. We find that the concentration of OH can be described by a surprisingly linear dependence on solar ultraviolet radiation throughout the measurement period, despite the fact that OH concentrations are influenced by thousands of reactants. A detailed numerical model of atmospheric reactions and measured trace gas concentrations indicates that the observed correlation results from compensations between individual processes affecting OH, but that a full understanding of these interactions may not be possible on the basis of our current knowledge of atmospheric chemistry. As a consequence of the stable relationship between OH concentrations and ultraviolet radiation that we observe, we infer that there is no long-term trend in the level of OH in the Hohenpeissenberg data set.

Marine aerosol, sea-salt, and the marine sulphur cycle a short review Marine aerosol, sea-salt, and the marine sulphur cycle a short review

Date added: 08/06/1997
Date modified: 07/02/2009
Filesize: 701.66 kB

O'Dowd, C. D., Lowe, J. A. & Smith, M. H. Marine aerosol, sea-salt, and the marine sulphur cycle: A short review. Atmos. Environ. 31, 73−80 (1997)


Abstract


A short review of the marine aerosol size distribution and the contribution of sea-salt to this distribution is presented. The potential role of sea salt in the marine boundary layer sulphur cycle is highlighted.

Aerosol dynamics in ship tracks Aerosol dynamics in ship tracks

Date added: 08/06/1999
Date modified: 07/23/2009
Filesize: 1.65 MB

Russell, L. M. ; Seinfeld, J. H. ; Flagan, R. C. ; Ferek, R. J. ; Hegg, D. A. ; Hobbs, P. V. ;  Wobrock, W. ;  Flossmann, A. I. ; O'Dowd, C. D. ; Nielsen, K. E. ; Durkee, P. A.  1999 Aerosol dynamics in ship tracks J. Geophys. Res. Vol. 104 , No. D24 , p. 31,077-31096 DOI 10.1029/1999JD900985


Abstract

 

Ship tracks are a natural laboratory to isolate the effect of anthropogenic aerosol emissions on cloud properties. The Monterey Area Ship Tracks (MAST) experiment in the Pacific Ocean west of Monterey, California, in June 1994, provides an unprecedented data set for evaluating our understanding of the formation and persistence of the anomalous cloud features that characterize ship tracks. The data set includes conditions in which the marine boundary layer is both clean and continentally influenced. Two case studies during the MAST experiment are examined with a detailed aerosol microphysical model that considers an external mixture of independent particle populations. The model allows tracking individual particles through condensational and coagulational growth to identify the source of cloud condensation nuclei (CCN). In addition, a cloud microphysics model was employed to study specific effects of precipitation. Predictions and observations reveal important differences between clean (particle concentrations below 150 cm-3) and continentally influenced (particle concentrations above 400 cm-3) background conditions: in the continentally influenced conditions there is a smaller change in the cloud effective radius, drop number and liquid water content in the ship track relative to the background than in the clean marine case. Predictions of changes in cloud droplet number concentrations and effective radii are consistent with observations although there is significant uncertainty in the absolute concentrations due to a lack of measurements of the plume dilution. Gas-to-particle conversion of sulfur species produced by the combustion of ship fuel is predicted to be important in supplying soluble aerosol mass to combustion-generated particles, so as to render them available as CCN. Studies of the impact of these changes on the cloud's potential to precipitate concluded that more complex dynamical processes must be represented to allow sufficiently long drop activations for drizzle droplets to form.

Characterization and intercomparison of aerosol absorption photometers: result of two intercompariso Characterization and intercomparison of aerosol absorption photometers: result of two intercompariso

Date added: 02/16/2011
Date modified: 02/16/2011
Filesize: 3.86 MB

Müller, T., Henzing, J. S., de Leeuw, G., Wiedensohler, A., Alastuey, A., Angelov, H., Bizjak, M., Collaud Coen, M., Engström, J. E., Gruening, C., Hillamo, R., Hoffer, A., Imre, K., Ivanow, P., Jennings, G., Sun, J. Y., Kalivitis, N., Karlsson, H., Komppula, M., Laj, P., Li, S.-M., Lunder, C., Marinoni, A., Martins dos Santos, S., Moerman, M., Nowak, A., Ogren, J. A., Petzold, A., Pichon, J. M., Rodriquez, S., Sharma, S., Sheridan, P. J., Teinilä, K., Tuch, T., Viana, M., Virkkula, A., Weingartner, E., Wilhelm, R., and Wang, Y. Q.: Characterization and intercomparison of aerosol absorption photometers: result of two intercomparison workshops, Atmos. Meas. Tech., 4, 245-268, doi:10.5194/amt-4-245-2011, 2011.


Absorption photometers for real time application have been available since the 1980s, but the use of filter-based instruments to derive information on aerosol properties (absorption coefficient and black carbon, BC) is still a matter of debate. Several workshops have been conducted to investigate the performance of individual instruments over the intervening years. Two workshops with large sets of aerosol absorption photometers were conducted in 2005 and 2007. The data from these instruments were corrected using existing methods before further analysis. The inter-comparison shows a large variation between the responses to absorbing aerosol particles for different types of instruments. The unit to unit variability between instruments can be up to 30% for Particle Soot Absorption Photometers (PSAPs) and Aethalometers. Multi Angle Absorption Photometers (MAAPs) showed a variability of less than 5%. Reasons for the high variability were identified to be variations in sample flow and spot size. It was observed that different flow rates influence system performance with respect to response to absorption and instrumental noise. Measurements with non absorbing particles showed that the current corrections of a cross sensitivity to particle scattering are not sufficient. Remaining cross sensitivities were found to be a function of the total particle load on the filter. The large variation between the response to absorbing aerosol particles for different types of instruments indicates that current correction functions for absorption photometers are not adequate.


In situ, gas chromatographic measurements of non-methane hydrocarbons and dimethyl sulfide at a In situ, gas chromatographic measurements of non-methane hydrocarbons and dimethyl sulfide at a

Date added: 08/05/1997
Date modified: 07/24/2009
Filesize: 587.14 kB

Lewis, A.C.; Bartle, K.D.; Heard, D.E.; McQuaid, J.B.; Pilling, M.J.; Seakins, P.W. (1997) In situ, gas chromatographic measurements of non-methane hydrocarbons and dimethyl sulfide at a remote coastal location (Mace Head, Eire) July-August 1996, Faraday Transactions, 93,  pp.2921-2927.


Abstract


Atmospheric non-methane hydrocarbons (NMHC) and dimethyl sulÐde (DMS) have been monitored at a remote coastal location Mace Head, Eire) using adsorption sampling techniques with analysis by in situ gas chromatography as part of the ACSOE OXICOA 1996 campaign. Concentrations varied considerably during the campaign but can be consistently interpreted by consideration of the relevant back-trajectory of the monitored air mass. Isoprene is conÐrmed as the most important NMHC in determining OH removal, contributing to up to 20%. Isoprene shows strong diurnal variations, although the structure of the diurnal pattern depends on the origin of the air mass. In contrast to previous studies, DMS concentrations during the campaign appeared to show no consistent diurnal variation.

Flood or Drought: How Do Aerosols Affect Precipitation? Flood or Drought: How Do Aerosols Affect Precipitation?

Date added: 09/12/2008
Date modified: 07/01/2009
Filesize: 1.93 MB

Flood or Drought: How Do Aerosols Affect Precipitation? Daniel Rosenfeld, Ulrike Lohmann, Graciela B. Raga, Colin D. O'Dowd, Markku Kulmala, Sandro Fuzzi, Anni Reissell, and Meinrat O. Andreae (5 September 2008) Science 321 (5894), 1309. [DOI: 10.1126/science.1160606]


Abstract


Aerosols serve as cloud condensation nuclei (CCN) and thus have a substantial effect on cloud properties and the initiation of precipitation. Large concentrations of human-made aerosols have been reported to both decrease and increase rainfall as a result of their radiative and CCN activities. At one extreme, pristine tropical clouds with low CCN concentrations rain out too quickly to mature into long-lived clouds. On the other hand, heavily polluted clouds evaporate much of their water before precipitation can occur, if they can form at all given the reduced surface heating resulting from the aerosol haze layer. We propose a conceptual model that explains this apparent dichotomy.

A detailed case study of isoprene chemistry during the EASE96 A detailed case study of isoprene chemistry during the EASE96

Date added: 08/05/2000
Date modified: 07/27/2009
Filesize: 349.47 kB

Carslaw, N., N. Bell, A.C. Lewis, J.B. McQuaid, and M.J. Pilling, 2000: A detailed case study of isoprene chemistry during the EASE96 Mace Head campaign. Atmos. Environ., 34, 2827-2836, doi:10.1016/S1352-2310(00)00088-1.


Abstract


A detailed chemical mechanism has been used in conjunction with high-quality field measurements in order to assess the potential role of isoprene at a clean coastal Northern Hemisphere site. The importance of isoprene as a source of peroxy radicals, formaldehyde and ozone is discussed in some detail for a case study day (July 17 1996). Between 10:00 and 16:00h GMT, isoprene accounts on average for 15% of the OH removal, yet is responsible for the production of about 30% of the HO2 radicals. Isoprene is also responsible for between 40-60% of the HCHO formation, and 20-40% of the 2 ppb h-1 conversion of NO to NO2 by peroxy radicals. We discuss the significant time lag between HCHO formation and destruction, a time lag that must be accounted for in order to accurately calculate the rate of HO2 production from isoprene degradation, and the implications of the isoprene oxidation for atmospheric chemistry.

 

Source apportionment of individual aerosol particles by using time-of-flight mass spectrometry Source apportionment of individual aerosol particles by using time-of-flight mass spectrometry

Date added: 08/06/2003
Date modified: 08/18/2008
Filesize: 7.67 kB

M. Dall Osto , R. M. Harrison , D. Beddows , R. P. Kinnesley , R. J. Donovan  and M. R. Heal, Source apportionment of individual aerosol particles by using time-of-flight mass spectrometry, 2003


Coastal New Particle Formation: A Review of the Current State-Of-The-Art Coastal New Particle Formation: A Review of the Current State-Of-The-Art

Date added: 08/01/2005
Date modified: 07/27/2009
Filesize: 773.65 kB

O’Dowd, C. D., T. Hoffmann, Coastal New Particle Formation: A Review of the Current State-Of-The-Art. Environ. Chem. 2, 245. doi:10.1071/EN05077, 2005.


Abstract


New particle formation via secondary gas-to-particle conversion processes over the oceans is one of the main mechanisms controlling the marine aerosol number population; however, despite extensive effort over the years, this phenomenon is still not well quantified. Coastal new particle formation events are more frequent than open ocean events and consequently have been studied in greater detail. This review article summarizes the recent studies into coastal new particle formation events and summarizes the linkage of these events to iodine emissions and ultimate particle formation via iodine oxide nucleation processes. The current state of knowledge may be summarized by concluding that, in general, coastal nucleation events are driven by biogenic emissions of iodine vapours that undergo rapid chemical reactions to produce condensable iodine oxides leading to nucleation and growth of new particles. The primary source of the condensable iodine vapours is thought to be molecular iodine (I2). The role of iodine oxides in open-ocean new particle production still remains an open question and is the most pressing next step to undertake.

Mesure de l'evaporation et de la radiation globale a St. Mortiz Mesure de l'evaporation et de la radiation globale a St. Mortiz

Date added: 08/07/1962
Date modified: 07/23/2009
Filesize: 1.21 MB
T.C O Connor ,Mesure de l'evaporation et de la radiation globale a St. Mortiz , Geofisica e Meteorologia Vol X  1962

Abstract


Biogenically-driven organic contribution to marine aerosol Biogenically-driven organic contribution to marine aerosol

Date added: 08/01/2004
Date modified: 07/27/2009
Filesize: 296.9 kB

O'Dowd, C.D., M.C. Facchini, F. Cavalli, D. Ceburnis, M. Mircea, S. Decesari, S. Fuzzi, Y.J. Yoon, and J.P. Putaud, Biogenically-driven organic contribution to marine aerosol, Nature, doi:10.1038/nature02959,. 2004.


Abstract


Marine aerosol contributes significantly to the global aerosol load and consequently has an important impact on both the Earth's albedo and climate. So far, much of the focus on marine aerosol has centred on the production of aerosol from sea-salt1 and non-sea-salt sulphates2, 3. Recent field experiments, however, have shown that known aerosol production processes for inorganic species cannot account for the entire aerosol mass that occurs in submicrometre sizes4, 5, 6. Several experimental studies have pointed to the presence of significant concentrations of organic matter in marine aerosol7, 8, 9, 10, 11. There is some information available about the composition of organic matter12, 13, 14, but the contribution of organic matter to marine aerosol, as a function of aerosol size, as well as its characterization as hydrophilic or hydrophobic, has been lacking. Here we measure the physical and chemical characteristics of submicrometre marine aerosol over the North Atlantic Ocean during plankton blooms progressing from spring through to autumn. We find that during bloom periods, the organic fraction dominates and contributes 63% to the submicrometre aerosol mass (about 45% is water-insoluble and about 18% water-soluble). In winter, when biological activity is at its lowest, the organic fraction decreases to 15%. Our model simulations indicate that organic matter can enhance the cloud droplet concentration by 15% to more than 100% and is therefore an important component of the aerosol–cloud–climate feedback system involving marine biota.

Accelerated Rates of Rainfall Accelerated Rates of Rainfall

Date added: 07/09/1971
Date modified: 06/30/2009
Filesize: 384.37 kB
P. R. BRAZIER-SMITH, S. G. JENNINGS & J. LATHAM, Accelerated Rates of Rainfall,  Nature 232, 112 - 113 (09 July 1971); doi:10.1038/232112b0

Abstract

 

RAINFALL intensity within clouds may be greatly increased by the production of satellite drops when raindrops collide, and this process could explain the extremely high rates of rainfall development reported in certain clouds1,2. We have set out to test this possibility by laboratory experiments.

A comparison of PM10 levels at mace head and at Trinity College Dublin A comparison of PM10 levels at mace head and at Trinity College Dublin

Date added: 08/07/2000
Date modified: 07/27/2009
Filesize: 102.39 kB

Finnan J.; McGovern F.M.; O'Leary B.; O'Donnell C.,A comparison of PM10 levels at mace head and at Trinity College Dublin,Journal of Aerosol Science, Volume 31, Supplement 1, September 2000 , pp. 887-888(2)


Abstract


In recent years the role of particulate matter in environmental and health areas has come under increased attention from regulatory and monitoring agencies. This has lead to the introduction of an EC directive on monitoring of PM10 (particulate matter size less than 10 p,m) levels for EU countries. However, the use of PM 10 as a measurement standard has been the subject of considerable debate with lower cut off points, e.g. 2.5 p,m (PM2.5) being considered by many to be of more directly relevant to health issues. Here we present an analysis of PM 10 measurements carried out at two very different sites, i.e. the background site at Mace Head and the central Dublin site of Trinity College Dublin (TCD). Concurrent size distribution data are used to examine the results.

Ionization equilibrium in aerosols Ionization equilibrium in aerosols

Date added: 01/01/1961
Date modified: 07/24/2009
Filesize: 3.34 MB
O'Connor, T.C. , Flanagan, V.P., Ionization equilibrium in aerosols, Geofisica Pura E Applicata - Milano, Vol. 50 (1961), pp. 148-154.

Abstract


Theoretical and experimental investigations were made on the time taken to achieve equilibrium charge distribution on Aitken nuclei. Theory indicates that the fraction of nuclei uncharged approaches its equilibrium value exponentially, with an approximate half time value of 0.693Z/4q and experiment gave good agreement with theory. The efficiency of a polonium-210 alpha ray source in producing ionization equilibrium in aerosols was examined and confirmed. The application of the methods described to the determination of the size of nuclei and to other observations in the free atmosphere are discussed.

Biogenic fluxes of halomethanes from Irish peatland ecosystems Biogenic fluxes of halomethanes from Irish peatland ecosystems

Date added: 08/06/2001
Date modified: 07/01/2009
Filesize: 278.07 kB

Dimmer, C.H., P.G. Simmonds, G.N. Nickless, and M.R. Bassford, Biogenic fluxes of halomethanes from Irish Peatland Ecosystems, Atmos. Environ., 35(2), 321-330, 2001, (Ser. No. ACP108)


Abstract


Irish peatland ecosystems have been shown to be important sources of low molecular weight halocarbons. Emission of CH3Br, CH3Cl, CH3I and CHCl3 was recorded from all peatland sites monitored, with minor flux of other halocarbons at certain sites. Fluxes were found to be highly linked to incident light, with strong diurnal cycles recorded at all open peatland sites. Estimates of halomethane emissions, particularly from coastal peatland and conifer plantation forest floor sites, suggests that these ecosystems may make a significant contribution to the global budgets of several important halocarbons. Global annual fluxes of 4.7 (0.1-151.9), 0.9 (0.1-3.3), 5.5 (0.9-43.4), and 1.4 (0.1-12.8) Ggyr-1 for CHCl3, CH3Br, CH3Cl, and CH3I, respectively, were determined for peatland ecosystems.

 

Modeling sea-salt aerosols in the atmosphere 1. Model development Modeling sea-salt aerosols in the atmosphere 1. Model development

Date added: 08/06/1997
Date modified: 07/23/2009
Filesize: 1.25 MB

Gong, S. L., L. A. Barrie, and J.-P. Blanchet (1997), Modeling sea-salt aerosols in the atmosphere 1. Model development, J. Geophys. Res., 102(D3), 3805–3818.


Abstract


A simulation of the processes of sea-salt aerosol generation, diffusive transport, transformation, and removal as a function of particle size is incorporated into a one-dimensional version of the Canadian general climate model (GCMII). This model was then run in the North Atlantic between Iceland and Ireland during the period of January-March. Model predictions are compared to observations of sea-salt aerosols selected from a review of available studies that were subjected to strict screening criteria to ensure their representativeness. The number and mass size distribution and the wind dependency of total sea-salt aerosol mass concentrations predicted by the model compare well with observations. The modeled dependence of sea-salt aerosol concentration in the surface layer (χ, μg m−3) on 10-m wind speed (U 10, m s−1) is given by χ = beaU10 . Simulations show that both a and b change with location. The value a and b range from 0.20 and 3.1 for Mace Head, Ireland to 0.26, and 1.4 for Heimaey, Iceland. The dependence of χ on surface wind speed is weaker for smaller particles and for particles at higher altitudes. The residence time of sea-salt aerosols in the first atmospheric layer (0–166 m) ranges from 30 min for large particles (r = 4–8 μm) to ∼60 hours for small particles (r = 0.13–0.25 μm). Although some refinements are required for the model, it forms the basis for comparing the simulations with long-term atmospheric sea-salt measurements made at marine baseline observatories around the world and for a more comprehensive three-dimensional modeling of atmospheric sea-salt aerosols.

 

Remote Sensing of Air Pollution Remote Sensing of Air Pollution

Date added: 08/07/1979
Date modified: 07/06/2009
Filesize: 1.35 MB

O'Connor T.C,Remote Sensing of Air Pollution , Proceedings of Seminar: Airpollution- Impacts and Controls, National Board for Science and Technology, 1979, pp. 93-96


Abstract

 

Recent technological advances have enabled man to extend his remote sensing capabilities from looking at the visible world around him into other parts of the Electromagnetic spectrum and his vantage point from a tower or hill to an orbiting satellite. one can now stufy air pollution problems over widespread areas and at all levels in the atmosphere. The techniques used are reviewed briefly and their application to air pollution in the lower atmosphere considered.

Remote sensing instruments may be categorised by the region of the electromagnetic spectrum concerned; the purpose for which they are used the mode of action as passive or active; the signal recovery and data handling techniques; the platform used - ground, aircraft or satellite; and or fixed location instruments. Remote sensing techniques can be used to study aerosols and/or specific gases. They may be used to study pollution distribution in the horizontal and vertical directions, general air quality, plume tracking, source monitoring and other applications. Their advantages and disadvantages for air quality management are given.

Performance of a venturi dilution chamber for sampling 3-20 nm particles Performance of a venturi dilution chamber for sampling 3-20 nm particles

Date added: 08/01/2005
Date modified: 07/23/2009
Filesize: 207.08 kB

Yoon, Y.J., S. Cheevers, S.G. Jennings, C.D. O’Dowd, Performance of a venturi dilution chamber for sampling 3-20 nm particles. J. Aerosol Science, 2005, 36(4), pp 535-540. doi:10.1016/j.jaerosci.2004.10.004


Abstract


The transmission efficiency of a venturi mixing and dilution system was investigated with laboratory generated aerosol by comparison of two condensation particle counters (CPCs). The transmission efficiency exceeded 95% for particle sizes between 3 and 20 nm. The use of the diluter system is demonstrated through comparison with total concentrations derived from a nano-scanning mobility particle sizer (nSMPS) applied to measuring a rapidly changing atmospheric nucleation mode. The study indicates that the diluted-CPC sampler can resolve rapidly changing, and more intense peaks in excess of 106 cm-3, which are otherwise missing or under-sampled by the nSMPS.

On the ability of pseudo-operational ground-based Light Detection And Ranging (LIDAR) sensors to det On the ability of pseudo-operational ground-based Light Detection And Ranging (LIDAR) sensors to det

Date added: 08/05/2011
Date modified: 08/05/2011
Filesize: 3.35 MB

Milroy, C., Martucci, S. Lolli,  S. Loaec, L. S. I. Xueref-Remy, J. V. Lavrič, C.D. O’Dowd,  On the ability of pseudo-operational ground-based Light Detection And Ranging (LIDAR) sensors to determine boundary-layer structure: intercomparison and comparison with in-situ radiosounding, Atmos. Meas. Tech. Diss.. 1–35, 2011 www.atmos-meas-tech discuss.net/4/1/2011/doi:10.5194/amtd-4-1-2011, 2011

 


 

Twenty-one cases of boundary-layer (BL) structure were retrieved by three co-located remote sensors, one lidar (Leosphere ALS300) and two ceilometers (Vaisala CL31, Jenoptik CHM15K). Data were collected during the ICOS field campaign held at the

GAW Atmospheric Station of Mace Head, Ireland, from 8 to 28 June 2009. The study is a two-step investigation of the BL structure based (i) on the intercomparison of backscatter pofiles from the three laser sensors and (ii) on the comparison of the backscatter profiles with twenty-three radiosoundings performed during the period of 8 to 15 June 2009. The Temporal Height-Tracking (THT) algorithm was applied to the three sensors’ backscatter profiles to retrieve the decoupled structure of the BL over Mace Head. The results of the intercomparisons are expressed in terms of the mean correlation coefficients, mean bias (difference between two sensors’ detections), mean sigma (the standard deviation of the bias) and the consistency, i.e. the percentage of cases where the detections of the intercompared sensors were closer than 200 m.  The ALS300-CHM15K comparison provided the most consistent retrievals amongst the three comparisons with, respectively, the 86.5% and 77.2% of the lower and upper layer detections closer than 200m and with correlation coefficients equal to 0.88 and 0.83 at the lower and upper layer, respectively. The lidar and ceilometers-detected BL heights were then compared to the temperature profiles retrieved by radiosoundings. The most consistent retrievals at the lower layer are from the ALS300 with the 75% of  detections closer than 200m to the radiosoundings’ first temperature inversion. Despite the lower signal-to-noise ratio and R-value compared to the ASL300 and CHM15K, the CL31 is more consistent with  the soundings retrievals at the upper layer with 62.5% of detections closer than 200m to the radiosoundings’ econd temperature inversion. The ALS300 has larger pulse-averaged power compared to the two ceilometers and better ability in detecting fine aerosol layers within the BL. The comparison of remote and in-situ data proved both the veracity of the inherent link between temperature and aerosol backscatter profiles, and the existence of possible limitations in using aerosols as a tracer to detect the BL structure. 

Measurements of gas-phase hydrogen peroxide and methyl hydroperoxide in the coastal environment duri Measurements of gas-phase hydrogen peroxide and methyl hydroperoxide in the coastal environment duri

Date added: 09/14/2002
Date modified: 07/02/2009
Filesize: 313.1 kB
Morgan, R. B., and A. V. Jackson (2002), Measurements of gas-phase hydrogen peroxide and methyl hydroperoxide in the coastal environment during the PARFORCE project, J. Geophys. Res., 107(D19), 8109, doi:10.1029/2000JD000257.

Abstract


Ambient gas-phase hydrogen peroxide (H2O2) and organic hydroperoxides (ROOHs) were measured at Mace Head Atmospheric Monitoring Station during September 1998 and June 1999. These measurements formed part of the New Particle Formation and Fate in the Coastal Environment (PARFORCE) campaign with the intention of assisting with the elucidation of potential oxidation pathways that lead to the production of new particles. A reflux concentrator sampled ambient air prior to on-site analysis by a peroxidase fluorescence technique with specific peroxide detection. Hydrogen peroxide, methyl hydroperoxide (CH3OOH), and several hydroperoxide species were detected. The highest H2O2 concentrations were observed during periods of clean maritime air, and a significant correlation exists between H2O2 concentration and tidal cycle during days when air masses had advected over inter tidal zones upwind of Mace Head. Peak H2O2 concentrations were observed around low tide on these days, coincident with particle events.

A global black carbon aerosol model A global black carbon aerosol model

Date added: 07/31/1996
Date modified: 07/27/2009
Filesize: 1.35 MB
Cooke W.F. and J.J.N. Wilson. (1996)- A global black carbon aerosol model, J. Geophys. Res., 101, 19395-19409.

Abstract


A global inventory has been constructed for emissions of black carbon from fossil fuel combustion and biomass burning. This inventory has been implemented in a three-dimensional global transport model and run for 31 model months. Results for January and July have been compared with measurements taken from the literature. The modeled values of black carbon mass concentration compare within a factor of 2 in continental regions and some remote regions but are higher than measured values in other remote marine regions and in the upper troposphere. The disagreement in remote regions can be explained by the coarse grid scale of the model (10° × 10°), the simplicity of the current deposition scheme, and possibly too much black carbon being available for transport, which would also account for the disagreement in the upper troposphere. The disagreement may also be due to problems associated with the measurement of black carbon. Emissions from this database appear to provide a reasonable estimate of the annual emissions of black carbon to the atmosphere. Biomass burning emissions amount to 5.98 Tg and that from fossil fuel amounts to 7.96 Tg. A local sensitivity analysis has been carried out and shows that black carbon has a lifetime between 6 and 10 days, depending on the transformation rate between hydrophobic and hydrophilic black carbon.

Aerosol properties associated with air masses arriving into the North East Atlantic during the 2008 Aerosol properties associated with air masses arriving into the North East Atlantic during the 2008

Date added: 11/10/2010
Date modified: 11/10/2010
Filesize: 7.27 MB

Dall’Osto,M.,  D. Ceburnis, G. Martucci, J. Bialek, R. Dupuy, S. G. Jennings, H. Berresheim, J. C. Wenger, R. M. Healy, M. C. Facchini, M. Rinaldi, L. Giulianelli, E. Finessi, D. Worsnop, M. Ehn, J. Mikkil¨a, M. Kulmala, J. Sodeau, and C. D. O’Dowd, , Aerosol properties associated with air masses arriving into the North East Atlantic during the 2008 Mace Head EUCAARI intensive observing period: an overview Atmos. Chem. Phys., 10, 8413-8435, doi:10.5194/acp-10-8413-2010, 2010.


Abstract.

 

As part of the EUCAARI Intensive Observing Period, a 4-week campaign to measure aerosol physical, chemical and optical properties, atmospheric structure, and cloud microphysics was conducted from mid-May to mid-June, 2008 at the Mace Head Atmospheric Research Station, located

at the interface of Western Europe and the N. E. Atlantic and centered on the west Irish coastline. During the campaign, continental air masses comprising both young and aged continental plumes were encountered, along with polar, Arctic and tropical air masses. Polluted-continental aerosol

concentrations were of the order of 3000 cm

 

3, while background marine air aerosol concentrations were between 400– 600 cm3. The highest marine air concentrations occurred in polar air masses in which a 15 nm nucleation mode, with concentration of 1100 cm3, was observed and attributed to open ocean particle formation. Continental air submicron chemical composition (excluding refractory sea salt) was dominated by organic matter, closely followed by sulphate mass.  Although the concentrations and size distribution spectral shape were almost identical for the young and aged continental cases, hygroscopic growth factors (GF) and cloud condensation nuclei (CCN) to total condensation nuclei (CN) concentration ratios were significantly less in the younger pollution plume, indicating a more oxidized organic component to the aged continental plume. The difference in chemical composition and hygroscopic growth factor appear to result in a 40–50% impact on aerosol scattering coefficients and Aerosol Optical Depth, despite almost identical aerosol microphysical properties in both cases, with the higher valuesb been recorded for the more aged case. For the CCN/CN ratio, the highest ratios were seen in the more age plume. In marine air, sulphate mass dominated the sub-micron component, followed by water soluble organic carbon, which, in turn, was dominated by methanesulphonic acid (MSA). Sulphate concentrations were highest in marine tropical air – even higher than in continental air. MSA was present at twice the concentrations of previously-reported concentrations at the same location and the same season. Both continental and marine air exhibited aerosol GFs significantly less than ammonium sulphate aerosol pointing to a significant organic contribution to all air mass aerosol properties.

Attenuated total Reflectance Measurements of the complex refractive index of polystyrene latex at CO2 laser wavelengths Attenuated total Reflectance Measurements of the complex refractive index of polystyrene latex at CO2 laser wavelengths

Date added: 07/31/1981
Date modified: 06/30/2009
Filesize: 1.62 MB
Jennings, S.G. (1981)- Attenuated total Reflectance Measurements of the complex refractive index of polystyrene latex at CO2 laser wavelengths. J. Opt. Soc. Amer., 71, 923-927.
Abstract

 

Attenuated total reflectance (ATR) measurements of the complex refractive index m of 5, 10,15, 20, and 30% water suspensions of polystyrene latex are presented for CO2 laser wavelengths (measurements for the 30% suspension are for X =10.591 ,um only). The use of the Maxwell Garnet mixture rule for the real index and the imaginary index (at X = 9.305 ,um) and an extrapolation scheme for the remaining values of imaginary index yield the values m =
1.709 - 0.07i (X = 9.305 ,tm); m = 1.887 - 0.06i (X = 9.504 Arm); m = 1.705 - 0.04i (X = 9.694 ,um); m = 1.764 - 0.045i (X = 10.591 ,um). ATR measurements of the complex index of water and water-ammonium sulfate solutions are in reasonably good agreement with those previously published.

A graphical method for determining the dry-depositional component of aerosol samples and their A graphical method for determining the dry-depositional component of aerosol samples and their

Date added: 08/07/1997
Date modified: 07/27/2009
Filesize: 907.95 kB

Huang, S., K. Rahn, and R. Arimoto. 1997. A graphical method for determining the dry-depositional component of aerosol samples and their field blanks. Atmospheric Environment 31:3383-3394.


Abstract


During the Atmosphere/Ocean Chemistry Experiment (AEROCE), field blanks of certain elements in aerosol samples occasionally increased abruptly, always during periods of unusually high atmospheric concentrations. We hypothesized that the anomalous blanks were created by coarse aerosol entering the sampling shelters and depositing onto the blank filters. If so, samples taken nearby should have been similarly affected. To test this hypothesis, we developed a simple graphical method in which elemental masses in field blanks are plotted against elemental masses in pumped samples, and zones of proportionality between the two are sought. Data from Bermuda and Mace Head (coastal western Ireland) confirmed that depositional zones did indeed appear, but only for coarse-particle elements and only under certain conditions. Actual increases of crustal and pollution-derived elements agreed well with values predicted from settling velocities and sampling rates: blanks increased up to an order of magnitude or more but samples by less than 1%. Marine elements behaved like crustal elements in most samples but occasionally were much more enriched: blanks increased up to 30-fold and samples up to about 3%. It thus appears that when coarse-particle elements are present in high concentrations, their field blanks and samples may be measurably affected by dry deposition. Depending on the elements of interest, this dry deposition may have to be measured and the concentrations corrected.

 

Highlights of fifty years of atmospheric aerosol research at Mace Head Highlights of fifty years of atmospheric aerosol research at Mace Head

Date added: 09/23/2008
Date modified: 07/23/2009
Filesize: 2.08 MB

O’Connor, T.C., S.G. Jennings, and C.D. O’Dowd, Highlights from 50 years of Aerosol Measurements at Mace Head, Atmos. Res., 90, 338–355, doi:10.1016/j.atmosres.2008.08.014, 2008.


Abstract

 

This paper summarises the development and principal results of fifty years of research on aerosols in the marine atmosphere at Mace Head Atmospheric Research Station on the west coast of Ireland. It concentrates on the sources, physico-chemical properties, number and mass concentrations, size range, volatility and chemical composition of aerosols in different air masses. It also examines optical properties of the aerosols and their long-range transport.

Nolan–Pollak type CN counters in the Vienna aerosol workshop Nolan–Pollak type CN counters in the Vienna aerosol workshop

Date added: 07/31/2002
Date modified: 07/03/2009
Filesize: 321.73 kB

Gras, J.L., J. Podzimek, T.C. O'Connor, K-H Enderle, Nolan-Pollak type CN counters in the Vienna aerosol workshop. Atmos. Res. 62, 239-254, 2002.


Abstract

 

Three standard Nolan-Pollak (N-P) and a modified N-P design condensation nucleus (CN) counters were included in the Vienna Workshop on Intercomparison of Condensation Nuclei and Aerosol Particle counters. These counters came from diverse backgrounds, namely programs in USA, Europe and Australia. In this work, principles of the operation and previous history of calibration of the N-P expansion counter are briefly reviewed and comparisons between the particular counters used in the workshop are presented and discussed. Counting agreement was found to be very good between the N-P counters, typically better than ± 12% for a range of aerosol sizes and compositions from a minimum diameter of 4 nm. The independently calibrated GIV CNC-440 (modified N-P type counter) also agreed well with the N-P counters. The minimum size sensitivity of the N-P counter was examined showing a lower detection limit for insoluble (Ag) particles of around 2.6 ± 0.3 nm diameter.

Measurement of contaminant removal from skin using a portable fluorescence scanning system Measurement of contaminant removal from skin using a portable fluorescence scanning system

Date added: 08/01/2005
Date modified: 07/02/2009
Filesize: 189.8 kB

Hession, H, Byrne, MA, Cleary, S, Andersson, KG and J Roed. Measurement of contaminant removal from skin using a portable fluorescence scanning system. In press: Journal of Environmental Radioactivity, 2005.


Abstract


The residence time of particulate contamination on the human body is a factor that has an important impact on the accuracy of exposure assessment in the aftermath of an accidental release of radionuclides to the atmosphere. Measurements of particle clearance from human skin were made using an illumination system to excite fluorescence in labelled silica particles and a CCD camera and image processing system to detect this fluorescence. The illumination system consists of high-intensity light emitting diodes (LEDS) of suitable wavelengths arranged on a portable stand. The physically small size of the LEDs allows them to be positioned close to the fluorescing surface, thus maximising the fluorescent signal that can be obtained. The limit of detection was found to be 50 μg of tracer particle per cm2.

Experiments were carried out to determine the clearance rates of 10 μm and 3 μm particles from the skin. Results show that, in the absence of any mechanical rubbing of the skin, the clearance of particles from the skin followed an approximately exponential decay with a half-time of 1.5–7.8 h. Skin hairiness and degree of human movement were found, in addition to particle size, to have an important influence on particle fall-off rate.

Scavenging Of Sub-Micrometre Aerosol Particles By Water Drops Scavenging Of Sub-Micrometre Aerosol Particles By Water Drops

Date added: 07/31/1993
Date modified: 07/06/2009
Filesize: 1.36 MB

Byrne, M.A., and Jennings, S.G. (1993). - Scavenging of submicrometre aerosol particles by water drops. Atmos. Environ., 27A, 2099 - 2105.


Abstract


Experiments were carried out in order to measure the collection efficiencies, E, with which small-sized water drops (of radii between 400 and 500 um) carrying electrical charge, Q (from 5 x 10^-4 to 22 x 10^-11 C) collect monodisperse aerosol particles of radii between 0.35 and 0.88 um. The measured values of collection efficency were within the range 1-6% and were in good agreement with previous results. the measurements show an increase in aerosol particles radius, drop radius and drop charge

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