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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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The modeling of tropospheric methane How well can point measurements be reproduced by a global The modeling of tropospheric methane How well can point measurements be reproduced by a global

Date added: 08/06/2000
Date modified: 07/27/2009
Filesize: 1.69 MB

Houweling, S., F. Dentener, J. Lelieveld, B. Walter, and E. Dlugokencky, 2000: The modeling of tropospheric methane: How well can point measurements be reproduced by a global model? J. Geophys. Res., 105, 8981-9002, doi:10.1029/1999JD901149.


Abstract

 

Global model simulations of tropospheric methane are presented, using state of the art representations of its terrestrial sources. Parameters critical for its tropospheric sink and transport have been evaluated using CH3CCl3 and SF6. We assess how well available methane measurements can be reproduced by the model, and how model and measurements can most efficiently be compared. Using European Centre for Medium-Range Weather Forecasts reanalyzed meteorological fields, direct comparisons between model results and flask or in situ measurements are presented, as opposed to comparing multiannual averaged seasonal cycles and trends as was done in previous studies. When comparing monthly means derived from weekly flask sampling and the model, the agreement at stations as Bermuda East and Mace Head is improved if, instead of sampling the model at each model time step, samples are taken at the same times as the measurements were taken. A method is presented to estimate the potential influence of subgrid variability using a marked tracer that is emitted in the vicinity of observational stations only. From the contribution of this tracer to the computed methane concentration at a particular station, the potential contribution of subgrid sources can be estimated. Radon 222 is used to select baseline conditions in the model to improve the comparability of model and measurements when a clean air sector is selected for sampling. Comparisons of model results and measurements, screened for local influences and artifacts of wind sector selection, indicate that the model has in particular difficulty reproducing seasonal cycles at higher latitude stations of the Northern Hemisphere. Sensitivity simulations show that the simulated annual variation at these stations is sensitive to the parameterization of wetland emissions. Also at the South China Sea, model simulations point to errors in the representation of methane sources. Marked tracer simulations indicate that this is most likely related to emissions from natural wetlands and rice paddies, in line with recent inverse modeling and up-scaling estimates.

 

The Mean Free path of Air The Mean Free path of Air

Date added: 07/31/1988
Date modified: 07/08/2009
Filesize: 1.38 MB
Jennings, S.G. (1988). - The mean free path in air. J. Aerosol Sci., 19, 159 - 166.

Abstract


Values for the mean free path l in air are presented for temperatures 15, 20, 23 and 25°C for both dry air and moist air at relative humidities of 50 and 100%, at atmospheric pressure (1.01325 × 105 Pa) and at pressure 1 × 105 Pa. Use is made of an expression which minimizes the dependence on physical ‘constants’ for mean free path: image where μ is the viscosity of air, p is the density of air, P is the pressure and μ is a numerical factor equal to 0.4987445. Differences of up to 1.6% were obtained between the values of mean free path at 23°C from this work and that of other workers. Comparison between the Cunningham slip correction factor from the present work and that from other work shows differences up to 1.8%.

The Interaction of Falling Water drops:Coalescene The Interaction of Falling Water drops:Coalescene

Date added: 07/30/1972
Date modified: 07/08/2009
Filesize: 802.92 kB

Brazier-Smith, P.R., Jennings, S.G., and Latham, J. (1972)- The interaction of falling water drops: coalescence. Proc. Roy. Soc.., A326, 393-408.


Abstract


Experimental studies have been conducted of the interaction of falling water drops of radii R and r (R > r), density p and surface tension or colliding in air with a relative velocity U and a perpendicular distance X between the centre of one drop and the undeflected trajec- tory of the other. R and r were varied from 150 to 750 /m, R/r from 1.0 to 2.5, U from 0.3 to 3.0 m s-1 and X from 0 (head-on collisions) to the maximum value for contact, R+r. Four types of interaction were observed: (1) bouncing; (2) permanent coalescence; (3) coalescence followed by separation; (4) coalescence followed by separation and the formation of satellite drops. The principal effort was devoted to a study of the critical conditions under which drops will separate after coalescence. It was found that there was a critical value of X, denoted by Xc, below which the coalesced drops remained united and above which there was sufficient angular momentum for the drops to separate after coalescence. For a wide range of values of r, R and U the coalescence efficiency e = Xc(R + r)2 was found to lie between 0.1 and 0.4 for drops of identical size and about 0.2 and 0.6 for drops with Rlr = 2.0. A theoretical analysis based on energy concepts predicted that the coalescence efficiency is given by the equation = 2.40(Up f (r) wheref (Rlr) is a function which varies from 1.3 for Rlr = 1 and 3.8 for R/r = 3. The predic- tions of this equation were in excellent agreement with the experimental results over the entire range of conditions studied. Investigations are also described of the critical conditions for the bouncing of colliding drops, the influence of electric charges upon the interactions and the elongation and splitting of a rotating drop.

The influence of the complex index of refraction on the volume extinction, scattering and absorption The influence of the complex index of refraction on the volume extinction, scattering and absorption

Date added: 08/01/1977
Date modified: 07/08/2009
Filesize: 496.46 kB
The influence of the complex index of refraction on the volume extinction, scattering and absorption coefficient of particle size distributions. Topical Optical Society of America Meeting on Optical Propagation Through Turbulence, Rain and Fog, Boulder, Colorado, U.S.A., pp. WD  7-1  to  7-4.

Abstract

 


The influence of evaporation and drop-interaction on a rainshaft : Comments and Notes The influence of evaporation and drop-interaction on a rainshaft : Comments and Notes

Date added: 09/14/1974
Date modified: 07/08/2009
Filesize: 326.53 kB

Brazier-Smith, P.R., and Jennings, S.G., and Latham, J. (1974)- The influence of evaporation and drop-interaction on a rainshaft Reply. Quart. J. Roy. Met. Soc., 99, 704-722.


Abstract


Calculations have been made of the variations with fall-depth z of the liquid water content, L, rainfall rate, p, radar reflectivity, Z, drop concentration, NT, and raindrop size distribution n(r), within a steady-state rainshaft as a result of the evaporation and interaction of the drops. The interactions were described by a generalized stochastic equation which takes account, as described by Brazier-Smith, Jennings and Latham (1973), of the variation of coalescence efficiency s with drop radii R, r and the fact that satellite drops are produced when drops separate after collision. The relative humidity is assumed to fall linearly from 100 per cent at cloud base (z = 0, T = 8°C) with a gradient 8. The lapse rate within the rainshaft was taken to be 8°C krn- and the initial size distribution was generally given by the Marshall-Palmer equation. Calculations were made for 3 different situations in order to isolate the physical processes which most affect the rainfall:
(l), evaporation without interaction; (2) interaction without evaporation; (3) both interaction and evaporation. The calculations for Case (1) indicate that the numbers of drops in all size classes are diminished with increasing Z, with a preferential reduction at the small-radius end of the spectrum. In Case (2) the interactions of the raindrops introduce considerable detail into n(r), with bimodal curves associated with satellite drop production, the highly efficient consumption of small drops by larger ones and the variations of E and fall-velocity V with drop-radius r.
The main feature of the calculations for Case (3) is the rBle of coalescence in preserving within the spectrum a considerable amount of liquid water that would otherwise be lost by evaporation. For example, whereas the rainwater content at z = 1.5 km for 8 = 20 per cent km- and Lo = 1.0 gm m- is 0.28 gm m-3 if interactions are absent, their presence elevates L to 0.57 gm m-3 at this level. This retention effect is significant for all values considered of 8, L, p, and the initial slope of the raindrop size distribution (varied from half to twice that of the Marshall-Palmerequation). It is alsofound that the structure introduced into the size distributions as a result of interactions is partially smoothed out by evaporation, which replaces a substantial proportion of the smallest drops consumed by coalescence.

The influence of evaporation and drop-interaction on a rainshaft The influence of evaporation and drop-interaction on a rainshaft

Date added: 07/30/1973
Date modified: 07/08/2009
Filesize: 1.13 MB

Brazier-Smith, P.R., and Jennings, S.G., and Latham, J. (1973)- The influence of evaporation and drop-interaction on a rainshaft. Quart. J. Roy. Met. Soc., 99, 704-722.


Abstract


Calculations have been made of the variations with fall-depth z of the liquid water content, L, rainfall rate, p, radar reflectivity, Z, drop concentration, NT, and raindrop size distribution n(r), within a steady-state rainshaft as a result of the evaporation and interaction of the drops. The interactions were described by a generalized stochastic equation which takes account, as described by Brazier-Smith, Jennings and Latham (1973), of the variation of coalescence efficiency s with drop radii R, r and the fact that satellite drops are produced when drops separate after collision. The relative humidity is assumed to fall linearly from 100 per cent at cloud base (z = 0, T = 8°C) with a gradient 8. The lapse rate within the rainshaft was taken to be 8°C krn- and the initial size distribution was generally given by the Marshall-Palmer equation. Calculations were made for 3 different situations in order to isolate the physical processes which most affect the rainfall:
(l), evaporation without interaction; (2) interaction without evaporation; (3) both interaction and evaporation. The calculations for Case (1) indicate that the numbers of drops in all size classes are diminished with increasing Z, with a preferential reduction at the small-radius end of the spectrum. In Case (2) the interactions of the raindrops introduce considerable detail into n(r), with bimodal curves associated with satellite drop production, the highly efficient consumption of small drops by larger ones and the variations of E and fall-velocity V with drop-radius r.
The main feature of the calculations for Case (3) is the rBle of coalescence in preserving within the spectrum a considerable amount of liquid water that would otherwise be lost by evaporation. For example, whereas the rainwater content at z = 1.5 km for 8 = 20 per cent km- and Lo = 1.0 gm m- is 0.28 gm m-3 if interactions are absent, their presence elevates L to 0.57 gm m-3 at this level. This retention effect is significant for all values considered of 8, L, p, and the initial slope of the raindrop size distribution (varied from half to twice that of the Marshall-Palmerequation). It is alsofound that the structure introduced into the size distributions as a result of interactions is partially smoothed out by evaporation, which replaces a substantial proportion of the smallest drops consumed by coalescence.

The impact of the Montreal Protocol on halocarbon concentrations in northern hemisphere baselin The impact of the Montreal Protocol on halocarbon concentrations in northern hemisphere baselin

Date added: 08/07/1998
Date modified: 07/23/2009
Filesize: 550.28 kB

Derwent, RG, Simmonds, PG, O'Doherty, S, et al , The impact of the Montreal Protocol on halocarbon concentrations in northern hemisphere baseline and European air masses at Mace Head, Ireland over a ten year period from 1987-1996, ATMOS ENVIRON, 1998, Vol: 32, Pages: 3689 - 3702,


Abstract


The international concern following the discovery of Antarctic stratospheric ozone depletion has prompted unprecedented international action by governments to control the production, sales and usage of a range of ozone-depleting chemicals. These international treaty obligations include the Montreal Protocol and its London and Copenhagen Amendments. They address, amongst many halocarbon species, the chlorofluorocarbons: CFC-11, -12 and -113 and the chlorocarbons: carbon tetrachloride and methyl chloroform. These chemicals have been routinely monitored at the remote, baseline monitoring station at Mace Head on the Atlantic Ocean coast of Ireland as part of the GAGE/AGAGE programme. The available monitoring data for the period 1987-1996 are presented here with a view to confirming the extent of compliance with the above Protocols on a global and European basis. Daily wind direction sectors provided by EMEP are used to sort the halocarbon data into northern hemisphere baseline air and European polluted air masses and trends have been determined for each wind direction sector. Evidence of the European phase-out of halocarbon usage is clearly apparent in the sorted halocarbon concentrations. A simple climatological long-range transport and a sophisticated Lagrangian air parcel dispersion model have been used to interpret the Mace Head halocarbon measurements and to derive estimates of European emission source strengths for each year. These emission source strengths confirm that the phase-out of halocarbon manufacture and sales is being followed in Europe.

 

The Impact of Ship-Produced Aerosols on the Microstructure and Albedo of Warm The Impact of Ship-Produced Aerosols on the Microstructure and Albedo of Warm

Date added: 08/06/2000
Date modified: 07/08/2009
Filesize: 176.35 kB

Durkee, P. and co authors, 2000: The impact of ship-produced aerosols on the microstructure and albedo of warm marine stratocumulus clouds: A test of MAST hypotheses 1i and 1ii. J. Atmos. Sci., 57, 2554-2569.


Abstract


Anomalously high reflectivity tracks in stratus and stratocumulus sheets associated with ships (known as ship tracks) are commonly seen in visible and near-infrared satellite imagery. Until now there have been only a limited number of in situ measurements made in ship tracks. The Monterey Area Ship Track (MAST) experiment, which was conducted off the coast of California in June 1994, provided a substantial dataset on ship emissions and their effects on boundary layer clouds. Several platforms, including the University of Washington C-131A aircraft, the Meteorological Research Flight C-130 aircraft, the National Aeronautics and Space Administration ER-2 aircraft, the Naval Research Laboratory airship, the Research Vessel Glorita, and dedicated U.S. Navy ships, participated in MAST in order to study processes governing the formation and maintenance of ship tracks. This paper tests the hypotheses that the cloud microphysical changes that produce ship tracks are due to (a) particulate emission from the ship's stack and/or (b) sea-salt particles from the ship's wake. It was found that ships powered by diesel propulsion units that emitted high concentrations of aerosols in the accumulation mode produced ship tracks. Ships that produced few particles (such as nuclear ships), or ships that produced high concentrations of particles but at sizes too small to be activated as cloud drops in typical stratocumulus (such as gas turbine and some steam-powered ships), did not produce ship tracks. Statistics and case studies, combined with model simulations, show that provided a cloud layer is susceptible to an aerosol perturbation, and the atmospheric stability enables aerosol to be mixed throughout the boundary layer, the direct emissions of cloud condensation nuclei from the stack of a diesel-powered ship is the most likely, if not the only, cause of the formation of ship tracks. There was no evidence that salt particles from ship wakes cause ship tracks.

 

The Hohenpeissenberg aerosol formation experiment (HAFEX): a long-term study including size-resolved The Hohenpeissenberg aerosol formation experiment (HAFEX): a long-term study including size-resolved

Date added: 07/27/2003
Date modified: 07/27/2009
Filesize: 514.79 kB

Birmili W, Berresheim H, Plass-Dulmer C, Elste T, Gilge S, Wiedensohler A, Uhrner U, 2003. The Hohenpeissenberg aerosol formation experiment (HAFEX): a longterm study including size-resolved aerosol, H2SO4, OH, and monoterpenes measurements. Atmos. Chem. Phys. 3: 361–376.


Abstract

 

Ambient aerosol size distributions (> 3 nm) and OH, H2SO4, and terpene concentrations were measured from April 1998 to August 2000 at a rural continental site in southern Germany. New particle formation (NPF) events were detected on 18% of all days, typically during midday hours under sunny and dry conditions. The number of newly formed particles correlated significantly with solar irradiance and ambient levels of H2SO4. A pronounced anticorrelatation of NPF events with the pre-existing particle surface
area was identified in the cold season, often associated with the advection of dry and relatively clean air masses from southerly directions (Alps). Estimates of the particle formation rate based on observations were around 1 cm−3 s−1, being in agreement with the predictions of ternary homogeneous H2SO4-NH3-H2O nucleation within a few orders of magnitude. The experimentally determined nucleation mode particle growth rates were on average 2.6 nm h−1, with a fraction of 0.7 nm h−1 being attributed to the cocondensation of H2SO4-H2O-NH3. The magnitude of nucleation mode particle growth was neither significantly correlated
to H2SO4, nor to the observed particle formation rate. Turn-over rate calculations of measured monoterpenes and aromatic hydrocarbons suggest that especially the oxidation products of monoterpenes have the capacity to contribute to the growth of nucleation mode particles. Although a large number of precursor gases, aerosol and meteorological parameters were measured, the ultimate key factors controlling the occurence of NPF events could not be identified.

The First Condensation Nucleus Conference And Research In Dublin The First Condensation Nucleus Conference And Research In Dublin

Date added: 08/07/1985
Date modified: 08/18/2008
Filesize: 711.16 kB
 O Connor, The First Condensation Nucleus Conference And Research In Dublin, J Rech. Atmos., 19 (1985) 

The Eyjafjallajökull Ash Plume – Part II,  Forecasting the plume dispersion., The Eyjafjallajökull Ash Plume – Part II, Forecasting the plume dispersion.,

Date added: 11/17/2011
Date modified: 11/17/2011
Filesize: 2.21 MB

O’Dowd, C., S. Varghese, R. Flanagan, D. Martin, D. Ceburnis, J. Ovadnevaite, G. Martucci, J. Bialek, C. Monahan, H. Berresheim, A. Vaishya, T. Grigas, S. G. Jennings,  P. McVeigh, E. Moran, K. Lambkin, T. Semmler, and R. McGrath, The Eyjafjallajökull Ash Plume – Part II,  Forecasting the plume dispersion., 10.1016/j.atmosenv.2011.10.037, Atmos. Env. 2011.

 


The recent eruption of Iceland’s Eyjafjallajokull volcano caused extensive disruption across Europe. In this paper, we describe the volcanic ash parameterisation incorporated in the regional climate model (REMOTE) for forecasting volcanic ash dispersion. We investigate model sensitivity to emission parameters including eruption column height and vertical release distribution. Model results over a number of key ash incursion events are assessed in terms of agreement with both ground based measurements and retrieved LIDAR data at a number of European sites.

The Eyjafjallajökull Ash Plume – Part I:  Physical, Chemical and Optical Characteristics, The Eyjafjallajökull Ash Plume – Part I: Physical, Chemical and Optical Characteristics,

Date added: 11/17/2011
Date modified: 11/17/2011
Filesize: 4.93 MB

O’Dowd, C.D., Darius Ceburnis, J. Ovadnevaite, G. Martucci, J. Bialek, C. Monahan, H. Berresheim, A. Vaishya, T. Grigas, S. G. Jennings,  P. McVeigh, S. Varghese, R. Flanagan, D. Martin, E. Moran, K. Lambkin, T. Semmler, C. Perrino, and R. McGrath, The Eyjafjallajökull Ash Plume – Part I:  Physical, Chemical and Optical Characteristics, Atmos. Environ, doi:10.1016/j.atmosenv.2011.07.004, , 2011.

 

 


Abstract. The Eyjafjallajökull ash plume was detected at the Mace Head Atmospheric Research Station numerous times from April 19th till 18th May, 2010 following subsidence into, and dilution in, the boundary layer.  The three strongest of these events, lasting 12-18 hours, are analysed in detail in terms of physical, chemical and optical properties.  The ash size distribution was bimodal with a supermicron mode of 2.5 mm diameter for the one case where it was measured.  The submicron mode varied from 185 nm during the high-explosive phase to 395 nm during the low-explosive phase.  Non-sea-salt (nss)-sulphate mass was 2.5 times higher during the low-explosive phase. Total particle concentrations ranged from 760 cm-3 to 1247 cm-3 and were typical of clean air in the region.    Between 30% and 39% of submicron chemical mass (i.e. exclusive of water content) was ash primarily composed of silicon dioxide while accounting for the water content, the submicron aerosol was composed of primary ash (15%) , nss-sulphate  (25%) and water (55%).  Hygroscopic growth factors were characteristic of sulphate aerosol but revealed an internally-mixed aerosol pointing to a mix of predominantly primary ash, nss-sulphate and water.  For the majority of the ash plumes, all condensation nuclei (CN, diameter >10 nm) were activated into cloud condensation nuclei (CCN) at a supersaturation of 0.25%.  Aerosol absorption increased by about a factor of two in the plume, compared to background levels, while aerosol scattering coefficients increased by an order of magnitude.

The Evolution of Condensation Nucleus Counters The Evolution of Condensation Nucleus Counters

Date added: 08/07/2001
Date modified: 07/07/2009
Filesize: 7.48 MB
O'Connor Tom,  The Evolution of Condensation Nucleus Counters , The Aerosol Society Newsletter, pg 5-8, March 2001

Abstract

 


The Electrical conductivity within water droplet clouds The Electrical conductivity within water droplet clouds

Date added: 08/01/1975
Date modified: 07/22/2009
Filesize: 1.58 MB
Jennings,S.G.   (1975)- The electrical conductivity within water droplet clouds. Proc.  4th Conf. Static Electrification. Inst. Phys. Conf. Series, No 27,  34-43.

Abstract

 

Studies have been made of the reduction of small positive ion concentration, produced by a weak americium alpha source in the presence of small water droplet clouds. The droplet clouds which possessed values of clou-water content ranging from about 1.0 up to 6 g m-3 and mean radius from 0.75 up to approximately 2.25 μm were produced by a steam condenser method which yielded relatively stable clouds.

The efficency with which drizzle and precipitation sized drops collide with aerosol particles The efficency with which drizzle and precipitation sized drops collide with aerosol particles

Date added: 07/31/1991
Date modified: 07/10/2009
Filesize: 3.81 MB

McGann, B.T., and Jennings, S.G. (1991) - The efficiency with which drizzle and precipitation sized drops collide with aerosol particles. Atmos. Environ., 25A, 791 - 800.


Abstract


Vlaues of collision efficency and scavenging rates for drops interacting with aerosol particles are presented using more accurate flow fields than previous work and for a much greater number of drops than hitherto obtained. All calculations are performed at an Ambient temperature of 10C andatmospheric pressure of 900mb. Computations of collision efficency are performed for a drop radius range from 50 to 500 micrometre (um), for particle radius from 0.005 to 10um, for relative humidity values of 50,75,95 and 100% and for particle density of 1,1.5,2.0 and 2.5 x 10^3 kgm^-3. In addition the collision effiicency was also calculated fro elctric charges on the drop and particle and for an electric field, representive of typical thundercloud values. Combined use is made of a rigorous trajectory model together with a flux model and comparision is made between them in the overlap size region . Precipitation scavenging rates and the percentage of aerosol particles scavenged by precipitation drops described by Marshall-Palmer size distribution is also calculated.

The effect of physical and chemical aerosol properties on warm cloud droplet activation The effect of physical and chemical aerosol properties on warm cloud droplet activation

Date added: 08/01/2005
Date modified: 07/23/2009
Filesize: 1.02 MB

McFiggans, G., P. Artaxo, U. Baltensperger, H. Coe, M. C. Facchini, G. Feingold, S. Fuzzi, M. Gysel,, A. Laaksonen, U. Lohmann, T. F. Mentel, D. M. Murphy, C. D. O'Dowd, J. R. Snider and E. Weingartner, The effect of physical and chemical aerosol properties on warm cloud droplet activation, Atmospheric Chemistry and Physics Discussions, Vol. 5, pp 8507-8647, 2005.


Abstract


The effects of atmospheric aerosol on climate forcing may be very substantial but are quantified poorly at present; in particular, the effects of aerosols on cloud radiative properties, or the "indirect effects" are credited with the greatest range of uncertainty amongst the known causes of radiative forcing. This manuscript explores the effects that the composition and properties of atmospheric aerosol can have on the activation of droplets in warm clouds, so potentially influencing the magnitude of the indirect effect. The effects of size, composition, mixing state and various derived properties are assessed and a range of these properties provided by atmospheric measurements in a variety of locations is briefly reviewed. The suitability of a range of process-level descriptions to capture these aerosol effects is investigated by assessment of their sensitivities to uncertainties in aerosol properties and by their performance in closure studies. The treatment of these effects within global models is reviewed and suggestions for future investigations are made.

The effect of particle size distribution and complex index of refraction of atmospheric aerosols... The effect of particle size distribution and complex index of refraction of atmospheric aerosols...

Date added: 08/01/1981
Date modified: 07/10/2009
Filesize: 1.44 MB
Jennings, S.G. (1981)- The effect of particle size distribution and complex index of refraction of atmospheric aerosols in the visual range. Proc. of the Ninth International Conference in Atmospheric Aerosol, Condensation and Ice Nuclei, Galway University Press, 415 - 420.

Abstract

 

A comprehensive study has been made of the effect of particle size distribution and complex index of refraction on the visual range, with a wavelengrth lamada of 0.55 micrometres. Calculations were performed by using a generalized polydisperse Mie scattering theory, which makes the assumption that the particles are spherical. Several workers have shown that a lognormal distribution can well represent different types of atmospheric aerosol over a wide range of natural conditions. A lognormal distribution wth geometric mean radius rg varying from 0.005 to 10 micrometers and geometric standard deviation sigmag varying from 1.5 up to 3.0 was used in the calculations.

 


 

The effect of clouds on aerosol growth in the rural atmosphere The effect of clouds on aerosol growth in the rural atmosphere

Date added: 08/06/2000
Date modified: 07/07/2009
Filesize: 206.46 kB

Colin D. O'Dowd, Jason A. Lowe, Michael H. Smith, The effect of clouds on aerosol growth in the rural atmosphere, Atmospheric ResearchVolume 54, Issue 4, , August 2000, Pages 201-221.


Abstract


Measurements of accumulation mode aerosol in the atmospheric boundary layer under cloudy and cloud-free conditions, and in the lower free troposphere under cloud-free conditions, were conducted over the rural northwest of England. Normalised size distributions in the cloud-free boundary layer (CFBL) and the cloud-free free troposphere (CFFT) exhibited almost identical spectral similarities with both size distributions possessing a concentration peak mode-radius of 0.05 μm or less. By comparison, aerosol distributions observed in cloudy air exhibited a distinctive log-normal distribution with mode-radii occurring at 0.1 μm concomitant with a local minimum at 0.05 μm. The consistent and noticeable difference in spectral features observed between cloudy and cloud-free conditions suggest that a greater amount of gas-to-particle conversion occurs on cloudy days, presumably through in-cloud aqueous phase oxidation processes, leading to larger sized accumulation mode particles. Apart from the distinct difference between cloudy and cloud-free aerosol spectra on cloudy days, aerosol concentration and mass were observed to be significantly enhanced above that of the ambient background in the vicinity of clouds. Volatility analysis during one case of cloud processing indicated an increase in the relative contribution of aerosol mass volatile at temperatures characteristic of sulphuric acid, along with a smaller fraction of more volatile material (possibly nitric acid and/or organic aerosol). Growth-law analysis of possible growth mechanisms point to aqueous phase oxidation of aerosol precursors in cloud droplets as being the only feasible mechanism capable of producing the observed growth. The effect of cloud processing is to alter the cloud condensation nuclei (CCN) supersaturation spectrum in a manner which increases the availability of CCN at lower cloud supersaturations.

 

The concurrent observation of methyl iodide and dimethyl sulphide in marine air; implications f The concurrent observation of methyl iodide and dimethyl sulphide in marine air; implications f

Date added: 08/07/1998
Date modified: 07/23/2009
Filesize: 560.08 kB

Bassford, M.R., G. Nickless, P.G. Simmonds, A.C. Lewis, M.J. Pilling, and M.J. Evans, The concurrent observation of methyl iodide and dimethyl sulphide in marine air; implications for sources of atmospheric methyl iodide, Atmospheric Environment, 33 (15), 2373-2383, 1999.


Abstract


Continuous atmospheric measurements of methyl iodide and dimethyl sulphide were carried out at Mace Head, western Ireland, over a 4-week period in July 1996. The concurrent observations of methyl iodide and dimethyl sulphide reported here display a clear association, indeed statistical analysis indicated a very significant degree of covariance. A simple yet informative use of modelled 5-day back trajectories was employed in tandem with examination of local meteorology to illuminate the geographical source regions of methyl iodide and dimethyl sulphide. The interpretation of the atmospheric observations in terms of air-mass flow has elucidated part of the global methyl iodide cycle and provides evidence for two distinct source regions of methyl iodide: I. Under certain synoptic meteorological conditions, long-range transport of methyl iodide and dimethyl sulphide was observed from discrete areas of the sub-tropical Atlantic Ocean located in a region between 30-50°N and 20-50°W. 2. Measurements taken under different conditions led us to believe that there was an additional source of methyl iodide that influenced the Mace Head atmosphere, most likely produced by coastal macroalgae which inhabit waters off the western coast of Ireland.

 

The composition of nucleation and Aitken modes particles during coastal nucleation events evidence f The composition of nucleation and Aitken modes particles during coastal nucleation events evidence f

Date added: 08/01/2006
Date modified: 07/07/2009
Filesize: 3.14 MB

Vaattovaara, P., P. E. Huttunen, Y. J. Yoon, J. Joutsensaari, K. E. J. Lehtinen, C. D. O’Dowd, and A. Laaksonen,The composition of nucleation and Aitken modes particles during coastal nucleation events: evidence for marine secondary organic contribution, Atmos. Chem. Phys. Discuss., 6, 3337–3379, 2006.


Abstract


Newly-formed nanometer-sized particles have been observed at coastal and marine environments worldwide. Interestingly, organic species have so far not been detected in those newly-formed nucleation mode particles. In this study, we applied the UFO-TDMA (ultrafine organic tandem differential mobility analyzer) method to study the possible existence of an organic fraction in recently formed coastal nucleation mode particles (d<20 nm) at the Mace Head research station. Furthermore, effects of those nucleation events to potential CCN (cloud condensation nuclei) were studied. The coastal events were typical for the Mace Head region and they occurred at low tide conditions during efficient solar radiation and high biological activity (HBA, i.e. a high mass concentration of chlorophyll a of the ocean) in spring 2002. Additionally, a PHA-UCPC (pulse height analyzer ultrafine condensation particle counter) technique was used to study the composition of newly-formed particles formed in low tide conditions during a lower biological activity (LBA, i.e. a lower mass concentration of chlorophyll a of the ocean) in October 2002. The overall results of the UFO-TDMA and the PHA-UCPC measurements indicate that those coastally/marinely formed nucleation mode particles include a remarkable fraction of secondary organic products, beside iodine oxides, which are likely to be responsible for the nucleation. During clean marine air mass conditions, the origin of those secondary organic oxidation compounds can be related to marine/coastal biota and thus a major fraction of the organics may originate from biosynthetic production of alkenes such as isoprene and their oxidation by iodine, hydroxyl radical, and ozone. During modified marine conditions, also anthropogenic secondary organic compounds may contribute to the nucleation mode organic mass, in addition to biogenic secondary organic compounds. Thus, the UFO-TDMA results suggest that the secondary organic compounds may, in addition to being significant contributors to the nucleation mode processes, accelerate the growth of freshly nucleated particles and increase their survival probability to CCN and even larger radiatively active particle sizes. The results give new insights to the coastal/marine particle formation, growth, and properties. The marine biota driven secondary organic contributions to coastal/marine particle formation and composition can be anticipated in other species specific biologically active oceans and fresh-waters areas around the world and thus, they may be significant also to the global radiative bugdet, atmosphere-biosphere feedbacks, and climate change.

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.

The background atmospheric concentrations of cyclic perfluorocarbon tracers determined by negat The background atmospheric concentrations of cyclic perfluorocarbon tracers determined by negat

Date added: 08/07/2002
Date modified: 07/23/2009
Filesize: 164.57 kB

Simmonds, P. G., Greally, B. R., Olivier, S., Nickless, G., Cooke, K. M., and Dietz, R. N.  The background atmospheric concentrations of cyclic perfluorocarbon tracers determined by negative ion-chemical ionization mass spectrometry.  Atmos. Environ. 36, 2147-2156 (2002).


Abstract


The background atmospheric mixing ratios for a range of cyclic perfluorocarbons (cyclic-PFCs), widely used in atmospheric dispersion studies, have been measured by gas chromatography-mass spectrometry in negative ion-chemical ionization mode. Background concentrations range from <1fll-1 to >10fll-1, where femtolitre is expressed as parts in 1015 (ppqv). Because of their very long atmospheric lifetimes (>3000yr) the present day concentrations represent the accumulated emissions from all sources, although significant commercial production did not commence until the 1960s. Cyclic-PFCs are potent greenhouse gases; however, their atmospheric concentrations are currently so low as to make an insignificant contribution to global warming.

 

Ten years of CO2, CH4,CO and N2O fluxes over Western Europe inferred from atmospheric..,Ireland Ten years of CO2, CH4,CO and N2O fluxes over Western Europe inferred from atmospheric..,Ireland

Date added: 08/01/2008
Date modified: 07/23/2009
Filesize: 2.45 MB

Messager, C., Schmidt, M., Ramonet, M., Bousquet, P., Simmonds, P., Manning, A., Kazan, V., Spain, G., Jennings, S. G., and Ciais, P.: Ten years of CO2, CH4, CO and N2O fluxes over Western Europe inferred from atmospheric measurements at Mace Head, Ireland, Atmos. Chem. Phys. Discuss., 8, 1191-1237, 2008


Abstract


We estimated CO2, CH4, CO and N2O emission fluxes over the British Isles and Western Europe using atmospheric radon observations and concentrations recorded at the Mace Head Atmospheric Research Station between 1996 and 2005. We classified hourly concentration data into either long-range European or regional sources from Ireland and UK, by using local wind speed data in conjunction with 222Rn and 212Pb threshold criteria. This leads to the selection of about 7% of the total data for both sectors. We then used continuous 222Rn measurements and assumptions on the surface emissions of 222Rn to deduce the unknown fluxes of CO2, CH4, CO and N2O. Our results have been compared to the UNFCCC, EMEP and EDGAR statistical inventories and to inversion results for CH4. For Western Europe, we found yearly mean fluxes of 4.1±1.5 106 kg CO2 km−2 yr−1 , 11.9±2.0 103 kg CH4 km−2 yr−1, 12.8±4.2 103 kg CO km−2 yr−1 and 520.2±129.2 kg N2O km−2 yr−1, respectively, for CO2, CH4, CO and N2O over the period 1996–2005. The method based upon 222Rn to infer emissions has many sources of systematic errors, in particular its poorly known and variable footprint, uncertainties in 222Rn soil fluxes and in atmospheric mixing of air masses with background air. However, these biases are likely to remain constant in the long-term, which makes the method quite efficient to detect trends in fluxes. Over the last ten years period, the decrease of the anthropogenic CH4, CO and N2O emissions in Europe estimated by inventories (respectively −30%, −35% and −23%) is confirmed by the Mace Head data within 2%. Therefore, the 222Rn method provides an independent way of verification of changes in national emissions derived from inventories. Using European-wide estimates of the CO/CO2 emission ratio, we also found that it is possible to separate the fossil fuel CO2 emissions contribution from the one of total CO2 fluxes. The fossil fuel CO2 emissions and their trends derived in that manner agree very well with inventories.

Temporal patterns, sources, and sinks of C8-C16 hydrocarbons in the atmosphere of Mace Head, Ireland Temporal patterns, sources, and sinks of C8-C16 hydrocarbons in the atmosphere of Mace Head, Ireland

Date added: 08/30/2002
Date modified: 03/07/2010
Filesize: 758.23 kB
Sartin, J. H., C. J. Halsall, L. A. Robertson, R. G. Gonard, A. R. MacKenzie, H. Berresheim, and C. N. Hewitt (2002), Temporal patterns, sources, and sinks of C8-C16 hydrocarbons in the atmosphere of Mace Head, Ireland, J. Geophys. Res., 107(D19), 8099, doi:10.1029/2000JD000232.

Abstract


During the 1999 New Particle Formation and Fate in the Coastal Environment (PARFORCE) field campaign, 16 C8-C16 volatile organic compounds (VOCs) were identified in the coastal atmosphere of Mace Head, Ireland. Sampling took place over 24 days, with 12 VOCs routinely quantified. Concentrations were observed in the low <10–150 parts per trillion by volume range, with levels typically in the order of aldehydes > ketones ≥ n-alkanes. Concentrations of these compounds were also measured in shoreline surface seawater. No relationship was observed between atmospheric concentrations and high/low tide events. Many VOCs revealed a temporal pattern in the atmosphere, with highest concentrations measured during the early morning and lowest concentrations in the afternoon. The strongest pattern was observed for the n-alkanes. However, this was dependent on the prevailing air mass direction and the local meteorology. A Lagrangian box model was applied to assess this diurnal cycle, using seawater emissions as a source (based on the seawater concentrations and observed wind speeds), and depletion via OH radicals and dilution by entrainment as sinks (using measured [OH] and boundary layer height data). The model gave good agreement to the observed concentrations for selected air mass types, predicting the daytime decrease in VOC concentrations due to OH radical chemistry and boundary layer growth, and the subsequent increase in VOC concentrations toward evening as both oxidation chemistry diminished and the mixing layer height fell.

Surfactants and Submicron sea spray generation Surfactants and Submicron sea spray generation

Date added: 08/01/2006
Date modified: 07/07/2009
Filesize: 1.86 MB
Sellegri, K., C. D. O'Dowd, Y. J. Yoon, S. G. Jennings, and G. de Leeuw, Surfactants and submicron sea spray generation, J. Geophys. Res., 111, D22215, doi:10.1029/2005JD006658, 2006.

Abstract


Laboratory experiments have been carried out to elucidate the role of surfactants on the primary marine aerosol production of submicron marine aerosols. A synthetic surfactant SDS was used in conjunction with artificially generated seawater, and the resultant bubble-mediated aerosol produced was observed. At 23°C, the aerosol distribution resulting from the use of surfactant-free seawater comprised three modes: (1) a dominant accumulation mode at 110 nm; (2) an Aitken mode at 45 nm; and (3) a third mode, at 300 nm, resulting from forced bursting of bubbles. The forced bursting occurs when bubbles fail to burst upon reaching the surface and are later shattered by splashing associated with breaking waves and/or wind pressure at the surface. At 4°C, the accumulation mode diameter was reduced to 85 nm, the Aitken mode diameter was reduced to <30 nm and the 300 nm mode diameter was reduced to 200 nm. With the addition of SDS, the relative importance of the mode resulting from forced bursting increased dramatically. The laboratory results were compared to the observed seasonality of North Atlantic marine aerosol where a progression from mode radii minima in winter to maxima in summer is seen. The bimodality and the seasonality in modal diameter can be mostly explained by a combination of the three modes observed in the laboratory and their variation as a function of sea-surface temperature and seawater surfactant concentration. These results indicate that submicron primary aerosol modes would on a first approximation result from bubble bursting processes, although evidences of additional secondary processes leading, during summer, to a higher amplitude of the Aitken mode and mode 2 smoothed into mode 3 still need to be investigated.

Sulphur and nitrogen compounds in variable marine continental air masses at the southwest Europ Sulphur and nitrogen compounds in variable marine continental air masses at the southwest Europ

Date added: 08/05/1996
Date modified: 07/07/2009
Filesize: 1.16 MB

Pio et al., 1996. A.C. Pio, M.A. Cerqueira, L.M. Castro and M.L. Salgueiro , Sulphur and nitrogen compounds in variable Marine/Continental air masses at the Southwest European Coast. Atmospheric Environment 30 18 (1996), pp. 3115–3127.


Abstract


Measurements of atmospheric sulphur and nitrogen species were made on the west coast of Portugal, within the framework of BMCAPE project. Four research intensive campaigns took place between November 1993 and August 1994 and revealed pronounced seasonal cycles for DMS and MSA. Surprisingly high levels of DMS were detected during autumn (mean concentration : 776ngSm-3), possibly as a consequence of a later algae bloom or local marsh emissions. COS displayed a slight seasonal variation with mean concentrations ranging from 741 ngSm-3 in autumn up to 903 ngS m-3 in summer. On the basis of backward air mass trajectories and local meteorological data, samples were assigned into different classes of air masses. The lowest concentrations of SO2, nssSO42-, NH3, NH4+, HNO3, NO3- and NO2were found in air masses transported over the Atlantic Ocean and were about 3-10 times lower than those recorded in air masses from continental origin. Nevertheless, for many of the species, the mean concentrations in maritime air were still significantly higher than those previously recorded in remote marine sites, presumably owing to long-range transport of pollutants or contamination induced by mesoscale wind circulation.

 

Sulfur in the Atmosphere Sulfur in the Atmosphere

Date added: 07/27/1995
Date modified: 07/27/2009
Filesize: 3.37 MB
Berresheim H., Wine P.H, Davis D.D,Sulfur in the Atmosphere, 1995

Submicron Particle, Radon and Soot Carbon Characteristics over Northeast Atlantic Submicron Particle, Radon and Soot Carbon Characteristics over Northeast Atlantic

Date added: 08/01/1993
Date modified: 07/23/2009
Filesize: 1 MB

O'Dowd, C. D., M. H. Smith, and S. G. Jennings (1993), Submicron Particle, Radon, and Soot Carbon Characteristics Over the Northeast Atlantic, J. Geophys. Res., 98


Abstract


Atmospheric aerosol particles (0.05μm ≤ rdry ≤ 1.5μm), 222Rn, and soot carbon mass were measured on a cruise over the Northeast Atlantic (63°N, 8°W) during October and November 1989. An accumulation mode (AM) was present in all particle data and was characterized by a lognormal size distribution with parameters N cm−3 (total number concentration), rg μm (geometric mean radius) and σg (geometric standard deviation). For aerosol associated with the “cleanest” Northeast Atlantic maritime and Arctic air masses, the AM parameters were found to be 16 cm−3 ≤ N ≤ 48 cm−3, 1.32 ≤ σg ≤ 1.46, and 0.08 μm < rg < 0.09 μm, leading to AM masses of between 0.20 μg m−3 and 0.38 μg m−3. Clean background levels of soot carbon mass for maritime and Arctic air were estimated to be around 20 ng m−3 and were associated with particle size radii r ≤ 0.15 μm. Soot carbon mass showed an excellent correlation with AM number concentration (∝=0.93), demonstrating its usefulness as an air mass tracer and as an indicator of anthropogenic pollutant transport. By comparison, radon, which is often used for this purpose, exhibited a significantly poorer correlation (∝=0.60) for this region. Approximately 9% of the total AM mass was accounted for by soot carbon, regardless of air mass origin, suggesting that early winter marine aerosol in the remote North Atlantic is primarily of anthropogenic origin.

Sub-ppt Atmospheric Measurements Using PTV-GC-FID and realtime Digital Signal Processing Sub-ppt Atmospheric Measurements Using PTV-GC-FID and realtime Digital Signal Processing

Date added: 08/05/1998
Date modified: 07/27/2009
Filesize: 76.15 kB

J.B McQuaid, A.C Lewis and K.D Bartle. , Sub-ppt Atmospheric Measurements Using PTV-GC-FID and Real-Time Digital Signal Processing., Journal of High Resolution Chromatography:


Abstract


Automated on-line trace level measurements in the atmosphere have become possible over the past ten years due to developments in large volume injection technology and the increased availability of  non-cryogenic cooling devices using phenomena such as the Peltier effect. The analysis of hydrocarbon (HC) species in the atmosphere is a particularly challenging area where individual
ambient concentrations as low as 1 ppt may be encountered in clean tropical marine air. From measurements of hydrocarbon species taken in clean air it has been demonstrated that small but significant concentrations of some species remain constantly present. The presence of certain reactive alkene species even at levels below 5 ppt may have a significant impact on the oxidative capacity ofthe clean atmosphere. Whilst halogenated species have been routinely measured on-line at sub-ppt levels for several years, the analysis of HC species has been limited by the flame ionisation detector - the most popular detector for field measurements. The limiting parameter in using FID for trace determination is often the noise generated within the FID amplifier electronics rather than by the absolute detection limit of the FID itself.  The flame ionisation detector amplifier uses a high gain transimpedance stage which has three main sources of noise. The feedback resistor generates both Johnson and Shot noise. This noise passes through the output without amplification as the voltage gain of a transimpedance amplifier is essentially unity over the bandwidth of interest. The third source of noise is due to current noise generated within the amplifier input stages. This noise is subsequently amplified along with the signal. Determinations at very low concentrations using automatic peak height or area integration prove difficult to perform with reliability due to a combination of poor signal to noise and transient detector spikes. By increasing data acquisition sampling rates coupled to the application of a digital signal processing algorithm, the electrometer output can be bandwidth limited to a frequency which allows peak information to be accurately represented whilst substantially reducing noise of higher frequencies. The roll off rate of a digital filter is much greater than can be achieved using an analogue filter. A rejection of greater than 150 dB can be achieved with a pass band to stop band delta of a fraction of 1 Hz. The benefit of this is that chromatographic resolution and efficiency are not affected by the process, i.e. the peaks are not broadened. This communication reports a digital signal processing (DSP) unit tested in parallel to standard data capture system coupled to an automated trace analysis field GC instrument. The basic principle of DSP is to convert a dynamic analogue signal into discrete values by sampling at certain intervals, followed by the application of mathematical filter algorithms to remove any interference or noise that may be obscuring the desired signal. Once processed, the discrete signal may then be converted back to analogue if necessary. Comparison of data from both systems demonstrates a large enhancement in minimum detectable amount and improved integration reliability. Use of a DSP unit has resulted in a lowering of detection limits to allow automated sub-ppt measurements to be performed. Comparison of trace level analysis has shown that raw FID output logged straight to PC leads to a consistent overestimation of peak height of the order of 25% at low signal to noise levels. Post processing of chromatograms using enhancement in digital gain has also been performed. This has demonstrated that a significant amount of noise remaining following on-line processing is induced at the analogue input stage to PC data capture system.

Sub-micron sea-spray fluxes Sub-micron sea-spray fluxes

Date added: 08/01/2005
Date modified: 07/23/2009
Filesize: 134.74 kB
Geever, M., C. O’Dowd, S. van Ekeren, R. Flanagan, D. Nilsson, G. de Leeuw and U. Rannik, Sub-micron sea-spray fluxes. Geophysical Research Letters, Geophys. Res. Lett., 32, L15810, doi:10.1029/2005GL023081, 2005.

Abstract


Eddy covariance aerosol flux measurements were conducted at the Mace Head coastal station in the North East Atlantic. Footprint and micrometeorological analysis under clean marine air mass conditions indicated that fluxes representative of open ocean conditions could be derived during high tide conditions and an oceanic fetch. Sea-spray fluxes were derived for total particle sizes larger than 10 nm and total particle sizes larger than 100 nm (i.e. covering the Aitken and Accumulation mode). The source fluxes (F) were found to be strongly correlated with both wind speed (U) and friction velocity (u*), following, by convention, an exponential relationship (Log F = a U + c) relationship. Comparison of source fluxes at sizes larger than 10 nm and larger than 100 nm demonstrates that approximately 50% of the number flux can be attributed to the accumulation mode and 50% to the Aitken mode. At 10 ms−1 wind speeds, the total primary marine aerosol flux is of the order of 2 × 106 m−2 s−1, increasing to 20 × 106 m−2 s−1 at 20 ms−1.

Study of water-soluble atmospheric humic matter in urban and marine envirorments Study of water-soluble atmospheric humic matter in urban and marine envirorments

Date added: 08/01/2008
Date modified: 07/07/2009
Filesize: 406.61 kB
Krivácsy, Z., Kiss, G., Ceburnis, D., Jennings, G., Maenhaut, W., Salma, I., Shooter, D.,
Study of water-soluble atmospheric humic matter in urban and marine environments,
Atmospheric Research 87 (2008) 1–12.

Abstract


Recently, atmospheric humic matter or humic-like substances (HULIS) have been found in the water-soluble fraction of atmospheric aerosol sampled at different locations. Most of these locations were continental, non-urban sites. Therefore, in this work HULIS was studied in urban and marine environments. The atmospheric concentration varied over a wide range from 0.40 to 5.44 μg m-3, from the clean marine air (Mace Head, Ireland) to the heavily polluted winter urban atmosphere (Christchurch, New Zealand). In terms of carbon, ratio of HULIS was 19-51% of water-soluble organic carbon, and 10-22% of total carbon. Different spectroscopic techniques were applied for the physico-chemical characterisation of HULIS including relative aromaticity and molecular weight. Specific absorbance was observed to be much less variable than specific fluorescence, and consequently UV-VIS spectroscopy at λ>330 nm was recommended for rapid, semi-quantitative determination of HULIS in the water extracts of atmospheric aerosol. Application of a dual filter sampling system at one of the sampling sites has revealed a significant positive sampling artefact which calls for further systematic studies on this subject, and also supports the idea of a secondary organic aerosol formation mechanism of HULIS.

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.

Steady state modelling of hydroxyl radical concentrations at Mace Head during the EASE '97 camp Steady state modelling of hydroxyl radical concentrations at Mace Head during the EASE '97 camp

Date added: 08/06/2001
Date modified: 07/23/2009
Filesize: 564.23 kB
Savage, N.H., R.M. Harrison, P.S. Monks, and G. Salisbury, Steady state modelling of hydroxyl radical concentrations at Mace Head during the EASE '97 campaign. May 1997, Atmos.Env., 35(3), 515-524, 2001, (Ser. No. ACP111).

Abstract

 

Two different steady-state methods are applied to calculate OH radical concentrations based on the rates of known source and sink processes. The first method, which calculates only OH radical concentrations from measured data including HO2 gives good correlation with measured OH concentrations but overpredicts by 30%. The second method applied calculates OH, HO2 and RO2 radical concentrations simultaneously. This second method overestimates the measured concentrations of OH by almost 3 times. This apparent overprediction may be a result of calculated concentrations of HO2 which appear too high and may be indicative of a gap in our understanding of the relevant peroxy radical chemistry or a result of the limited peroxy radical chemistry assumed by the method.

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%.

Statistical Analysis of Eight Surface Ozone Measurement Series for various sites in Ireland, Statistical Analysis of Eight Surface Ozone Measurement Series for various sites in Ireland,

Date added: 02/08/2011
Date modified: 02/08/2011
Filesize: 1.81 MB

Tripathi, O. P., Jennings S. G., O’Dowd, C. D., Coleman, L., Leinert, S., O’Leary, B., Moran, E., O’Doherty, S. J., and Spain, T. G., Statistical Analysis of Eight Surface Ozone Measurement Series for various sites in Ireland, J. Geophys. Res., 115, D19302, doi:10.1029/2010JD014040., 2010


Abstract: Data from various stations having different measurement record periods between 1988 and 2007 are analyzed to investigate the surface ozone concentration, long‐term trends, and seasonal changes in and around Ireland. Time series statistical analysis is performed on the monthly mean data using seasonal and trend decomposition procedures and the Box‐Jenkins approach (autoregressive integrated moving average). In general, ozone concentrations in the Irish region are found to have a negative trend at all sites except at the coastal sites of Mace Head and Valentia. Data from the most polluted Dublin city site have shown a very strong negative trend of −0.33 ppb/yr with a 95% confidence limit of 0.17 pp/yr (i.e., −0.33 ± 0.17) for the period 2002−2007, and for the site near the city of Cork, the trend is found to be −0.20 ± 0.11 ppb/yr over the same period. The negative trend for other sites is more pronounced when the data span is considered from around the year 2000 to 2007. Rural sites of Wexford and Monaghan have also shown a very strong negative trend of −0.99 ± 0.13 and −0.58 ± 0.12, respectively, for the period 2000−2007. Mace Head, a site that is representative of ozone changes in the air advected from the Atlantic to Europe in the marine planetary boundary layer, has shown a positive trend of about +0.16 ± 0.04 ppb per annum over the entire period 1988−2007, but this positive trend has reduced during recent years (e.g., in the period 2001−2007). Cluster analysis for back trajectories are performed for the stations having a long record of data, Mace Head and Lough Navar. For Mace Head, the northern and western clean air sectors have shown a similar positive trend (+0.17 ± 0.02 ppb/yr for the northern sector and +0.18 ± 0.02 ppb/yr for the western sector) for the whole period, but partial analysis for the clean western sector at Mace Head shows different trends during different time periods with a decrease in the positive trend since 1988 indicating a deceleration in the ozone trend for Atlantic air masses entering Europe.

Sources and source variations for aerosol at Mace Head, Ireland Sources and source variations for aerosol at Mace Head, Ireland

Date added: 08/07/2001
Date modified: 07/23/2009
Filesize: 575.5 kB

JR Huang S., Arimoto R., Rahn K. A. (2000) Sources and source variations for aerosol at Mace Head, Ireland. Atmos. Environ. 35, 1421-1437.


Abstract


The sources and source variations for aerosol at Mace Head, Ireland, were studied by applying positive matrix factorization (PMF), a variant of factor analysis, to a 5-yr data set for bulk aerosol. Signals for the following six sources were evident year round: (1) mineral dust, (2) sea salt, (3) general pollution, (4) a secondary SO42--Se signal that is composed of both natural (marine) and pollution (coal) components, (5) ferrous industries, (6) and a second marine (possibly biogenic) source. Analyses of seasonally stratified data suggested additional sources for iodine and oil emissions but these were present only in certain seasons, respectively. The marine signal is particularly strong in winter. The main pollution transport from Europe to Mace Head occurs in May, but the influence of continental European emissions is evident throughout the year. Mineral aerosol evidently follows a transport pathway similar to that of pollution aerosol, i.e., recirculation via the westerlies brings pollutants mixed with dust to the site from nearby land, i.e., Ireland, the United Kingdom, and the Belgium, Netherlands, and Luxemburg (Benelux) region, with some inputs from Scandinavia, Western Europe, Eastern Europe, and even the Mediterranean region. Compared with Bermuda, aerosol at Mace Head has stronger marine sources (especially marine-derived secondary SO42- and Se) but weaker crustal and oil signals. Transport across the North Atlantic, especially in winter, cannot be ruled out.

Source assessment of particulate air pollutants measured at the southwest european coast Source assessment of particulate air pollutants measured at the southwest european coast

Date added: 08/05/1996
Date modified: 07/23/2009
Filesize: 841.66 kB

Pio, C.A., L.M. Castro, M.A. Cerqueira, I.M. Santos, F. Belchior, and M. L. Salgueiro,(1996), Source assessment of particulate air pollutants measured at the southwest , European coast, Atmos. Environ., 30, 3309-3320


Abstract


Aerosol particles and gaseous species were measured in air masses transported to the west coast of Portugal, between November 1993 and August 1994. Samples were taken during four monitoring campaigns distributed along the various seasons of the year, integrated in the EC Project : BMCAPE. Aerosol particles were collected with separation in two size fractions and analysed in relation to total mass, water soluble ions, trace elements and black/organic carbon. Local micro-meteorological parameters and air mass backward trajectories were compared with analytical results in order to define characteristic air mass types and to evaluate the origin of pollutants. Average concentrations on the Portuguese west coast, even in maritime air masses, are higher than values observed in remote oceanic locations. This is probably a consequence of continental European air masses recirculation through the eastern Atlantic Ocean, reinforced by situations of mesoscale transport from the Iberian Peninsula. Principal Component Analysis permitted the identification of five source groups for the fine and coarse aerosol fractions, namely combustion plus road traffic, sea salt spray, secondary aerosol production, soil and possibly non-ferrous metallurgy industries. In the aerosol fine fraction road traffic and combustion contribute on average with 250% of the total fine aerosol mass, while sea spray and secondary production represent 14% and 31%, respectively of the mass loading. Sea spray is by far the major contributor to the coarse fraction with an average of 88% of the suspended coarse aerosol mass.

 

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


Some Characteristics of condensation Nuclei stored in a large vessel Some Characteristics of condensation Nuclei stored in a large vessel

Date added: 08/07/1955
Date modified: 07/07/2009
Filesize: 1.44 MB
TC OConnor, Some Characteristics of condensation Nuclei stored in a large vessel ,Geofisica Pura E Apllicata- Milano Vol 31 pp 107-114 (1955)

Abstract

 

THe Coagulation coefficent, size and charge distribution of condensation nuclei from room air when stored in a 4000 litre rubber balloon gasometer were studied. The results indicate that the acquisation of water vapour contributes to the growth of stored nuclei. A preliminary trial was made to see if Junge's Approximate rule that the number of particles in an aerosol varies inversely as the third power of their radius, also holds for Aitken nuclei. Further cnfirmation of the relationship between the percentage of stored nuclei electrically charged and their average radius were obtained.

The measurements were carried out by means of the Pollak-Murphy improved version of the photo-electric nucleus counter. A statistical analysis based on over a thousand comparisions of two identical models shows that the agreement of individual readings is better than 10% of nucleus concentrations in 80% of all cases. Excessive differences have now been eliminated.

Small particle concentration fluctuations at a coastal site Small particle concentration fluctuations at a coastal site

Date added: 08/01/2002
Date modified: 07/23/2009
Filesize: 877.43 kB
Vana, M., Jennings, S.G., Kleefeld, C., Mirme, A., and Tamm, E., 2002. Small particle concentration fluctuations at a coastal site, Atmos. Res., 63, pp. 247 – 269.

Abstract


Aerosol size spectra (d=10 nm–10 μm) were measured with an electrical aerosol spectrometer (EAS) at Mace Head on the west coast of Ireland. Several small aerosol particle (diameter 10–32 nm) concentration bursts were observed during the measurement period. Relationships between the events, air mass trajectories, tide height, and meteorological parameters are examined. Series of bursts were observed when a spectral transformation due to subsequent particle growth from 10 to 56–100 nm can be identified in an Eulerian experiment. Particle growth rates of between 1 and 3 nm/h were determined. These bursts appear in cold and comparatively clean arctic or polar air masses with temperature and relative humidity fluctuations, and do not correlate with low tide in some cases. These episodes, similar to those frequently found in the continental boundary layer, are thought to occur over a wide area and, for clear detection, require stable airflow for a few days. Elevated small-particle concentration events are more common during low tide or shortly after, and are typically associated with low wind speeds. Here, the increased shore exposure during low tide is thought to influence the nucleation and the subsequent growth of these aerosol particles. The occurrences of the bursts are found to depend on local wind direction. The highest d=10–32 nm particle concentrations appeared for wind sectors furthest from the tidal regions when the wind direction was 150–160°(south-easterly). Most of the events occurred during daytime when solar irradiation is most intense.

Size-differentiated volatility analysis of internally mixed laboratory-generated aerosol, Size-differentiated volatility analysis of internally mixed laboratory-generated aerosol,

Date added: 08/01/2002
Date modified: 07/23/2009
Filesize: 348.8 kB
Brooks, B.J., M.H. Smith, M.K. Hill, and C.D. O'Dowd, Size-differenciated volatility analysis of internally mixed laboratory-generated aerosol, J. Aer. Sci.,33, 555-579, 2002.

Abstract


The increased application of volatility analysis to determine the composition and structure of sub-micron aerosol requires that the thermal behaviour of chemically complex aerosol be understood. Presented here is a volatility study, utilising a tandem volatility differential mobility analyser (TVDMA), of 30, 50, and 70nm radii, internally mixed, aerosol containing ionic-salts, acids, organics, and carbon. Evidence of some size-dependent behaviour was observed with several of the single component aerosol. Internally mixed aerosol displayed complex thermal behaviours that were dependent on both size and the volume mixing ratio of source solutions

Size Mobility Charge of multi charged Ions Size Mobility Charge of multi charged Ions

Date added: 08/07/1955
Date modified: 07/23/2009
Filesize: 4.14 MB
PJ Nolan and TC O'Connor ,Size Mobility Charge of multi charged Ions,  14 Dec 1955
Abstract

 

The experiments of J.J Nolan and J.G O'Keefe (1933) on multiply charged ions produced in various ways indicated that the mobility of these ions was independent of the charge. they suggusted the following way out of the difficulty: "It is possible that a nucleus on receiving a large electric charge, may in a moist atmosphere rapidly grow and adapt its size to its charge in such a way as to have approximately a constant mobility". the present research was designed to elucidate the problem by measureing the size as well as the mobility and charge of multiply charged ions. One of the methods of producing multiply charged ions used by Nolan and O'Keefe was the spraying of water. We found that production by bubblling was more convenient than production by spraying. During the course of the work certain features of the ionisation produced by bubbling were investigated. These investigations were not exhaustive since they were only incidental to the main purpose of the research.

SimulatingMarine New Particle Formation and Growth Using theM7Modal Aerosol DynamicsModal SimulatingMarine New Particle Formation and Growth Using theM7Modal Aerosol DynamicsModal

Date added: 01/30/2011
Date modified: 01/31/2011
Filesize: 1.28 MB

Monahan, C., H. Vuollekoski, M. Kulmala, C. O’Dowd. Modelling the Contribution of Iodine Oxide to Marine New Particle Formation, Adv. in Meteorol., Article ID 482603, doi:10.1155/2010/482603, 2010.


A modal atmospheric aerosol model (M7) is evaluated in terms of predicting marine new particle formation and growth. Simulations were carried out for three different nucleation schemes involving (1) kinetic self-nucleation of OIO (2) nucleation via OIO activation by H2SO4 and (3) nucleation via OIO activation by H2SO4 plus condensation of a low-volatility organic vapour. Peak OIO and H2SO4 vapour concentrations were both limited to 6 × 106 molecules cm−3 at noontime while the peak organic vapour concentration was limited to 12×106 molecules cm−3. All simulations produced significant concentrations of new particles in the Aitken mode. From a base case particle concentration of 222 cm−3 at radii >15 nm, increases in concentrations to 366 cm−3 were predicted fromthe OIO-OIO case, 722 cm−3 for the OIO-H2SO4 case, and 1584 cm−3 for the OIO-H2SO4 case with additional condensing organic vapours. The results indicate that open ocean new particle production is feasible for clean conditions; however, new particle production becomes most significant when an additional condensable organic vapour is available to grow the newly formed particles to larger sizes. Comparison to sectional model for a typical case study demonstrated good agreement and the validity of using the modal model.

Simulating ultrafine particle formation in Europe using a regional CTM: contribution of primary emissions versus secondary formation to aerosol number concentrations Simulating ultrafine particle formation in Europe using a regional CTM: contribution of primary emissions versus secondary formation to aerosol number concentrations

Date added: 03/21/2013
Date modified: 03/21/2013
Filesize: 2.01 MB

Fountoukis, C., I. Riipinen, H. A. C. Denier van der Gon, P. E. Charalampidis, C. Pilinis, A. Wiedensohler, C. O'Dowd, J. P. Putaud, M. Moerman, and S. N. Pandis, Simulating ultrafine particle formation in Europe using a regional CTM: contribution of primary emissions versus secondary formation to aerosol number concentrations, Atmos. Chem. Phys., 12, 8663–8677, 2012 www.atmos-chem-phys.net/12/8663/2012/ doi:10.5194/acp-12-8663-2012.


Abstract. A three-dimensional regional chemical transport model (CTM) with detailed aerosol microphysics, PMCAMx-UF, was applied to the European domain to simulate the contribution of direct emissions and secondary formation to total particle number concentrations during May 2008. PMCAMx-UF uses the Dynamic Model for Aerosol Nucleation and the Two-Moment Aerosol Sectional (TOMAS) algorithm to track both aerosol number and mass concentration using a sectional approach. The model predicts nucleation events that occur over scales of hundreds up to thousands of kilometers especially over the Balkans and Southeast Europe. The model predictions were compared against measurements from 7 sites across Europe. The model reproduces more than 70% of the hourly concentrations of particles larger than 10 nm (N10) within a factor of 2. About half of these particles are predicted to originate from nucleation in the lower troposphere. Regional nucleation is predicted to increase the total particle number concentration by approximately a factor of 3. For particles larger than 100 nm the effect varies from an increase of 20% in the eastern Mediterranean to a decrease of 20% in southern Spain and Portugal resulting in a small average increase of around 1% over the whole domain. Nucleation has a significant effect in the predicted N50 levels (up to a factor of 2 increase) mainly in areas where there are condensable vapors to grow the particles to larger sizes. A semi-empirical ternary sulfuric acid-ammonia-water parameterization performs better than the activation or the kinetic parameterizations in reproducing the observations. Reducing emissions of ammonia and sulfur dioxide affects certain parts of the number size distribution.

 

Significant growth in surface ozone at Mace Head, Ireland, 1987–2003 Significant growth in surface ozone at Mace Head, Ireland, 1987–2003

Date added: 08/07/2004
Date modified: 07/23/2009
Filesize: 501.27 kB

Significant growth in surface ozone at Mace Head, Ireland, 1987-2003 P.G. Simmonds, R.G. Derwent, A.L. Manning, G. Spain Atmos. Environ., 38, 4769-4778, 2004


Abstract

 

Background ozone O3 observations at Mace Head on the west coast of Ireland since 1987 show a significant positive trend of 0.49 ± 0.19 ppb year-1 through to 2003. Increasing trends are observed for all seasons, with the largest trends during the winter season, 0.63±0.31 ppb year-1 and the smallest trends during the summer, 0.39 ± 0.25 ppb year-1. However, this growth rate has not been consistent over time with a major anomaly evident in 1998-1999. This major O3 perturbation is correlated with variations of CO2, CO, CH4, H2 and CH3Cl, which are likely due to large-scale biomass burning events in tropical and boreal regions during 1997-1999 coupled with an intense El Niño event. Over the 16 years of observations background O3 has increased by about 8 ppb (∼ 24%) in the clean oceanic sectors representative of the Northern Hemisphere marine boundary layer.

 

Significant enhancement of aerosol optical depth in marine air under high wind conditions Significant enhancement of aerosol optical depth in marine air under high wind conditions

Date added: 09/12/2008
Date modified: 07/06/2009
Filesize: 479.23 kB

Mulcahy, J. P., C. D. O'Dowd, S. G. Jennings, and D. Ceburnis (2008), Significant enhancement of aerosol optical depth in marine air under high wind conditions, Geophys. Res. Lett., 35, L16810, doi:10.1029/2008GL034303.


Abstract


The relationship between the AOD and wind speed (U), obtained at the Mace Head atmospheric research station, is determined for clean marine (Northeast Atlantic) conditions under steady-state wind speed scenarios. AOD measurements were made under much higher wind speed conditions (up to 18 m s−1) than hitherto measured. The AOD is found to be approximately dependent on U2, with a high correlation (r2 = 0.97) determined at all measured wavelengths of 862 nm, 500 nm, 412 nm and 368 nm. A corresponding anti-correlation was observed between the Ångström exponent and wind speed (r2 = 0.93). The results illustrate that under moderate-to-high wind conditions, sea-spray AOD can rival or even exceed that associated with pollution plumes over oceanic regions and can potentially contribute to radiative, dynamical and biogeochemical feedback processes associated with future climate change.

 

Short-lived alkyl iodides and bromides at Mace Head, Ireland Links to biogenic sources and halo Short-lived alkyl iodides and bromides at Mace Head, Ireland Links to biogenic sources and halo

Date added: 08/05/1999
Date modified: 07/23/2009
Filesize: 944.76 kB

Carpenter, L., Hebestreit, K., Sturges, W., Penkett, S., Liss, P., Alicke, B., and Platt, U.: Observation of short-lived alkyl iodides and bromides at Mace Head, Ireland: links to biogenic sources and halogen oxide production, J. Geophys. Res., 104, 1679–1689, 1999. 6080, 6108


Abstract


Automated in situ gas chromatograph/mass spectrometer (GC/MS) measurements of a range of predominantly biogenic alkyl halides in air, including CHBr3, CHBr2Cl, CH3Br, C2H5Br, CH3I, C2H5I, CH2ICl, CH2I2, and the hitherto unreported CH2IBr were made at Mace Head during a 3-week period in May 1997. C3H7I and CH3CHICH3 were monitored but not detected. Positive correlations were observed between the polyhalomethane pairs CHBr3/CHBr2Cl and CHBr3/CH2IBr and between the monohalomethane pair CH3I/C2H5I, which are interpreted in terms of common or linked marine sources. During periods when air masses were affected by emissions from local seaweed beds, the concentrations of CHBr3, CH2ICl, and CH2IBr not only showed remarkable correlation but also maximized at low water. These are the first field observations to provide evidence for a link between the tidal cycle, polyhalomethanes in air, and potential marine production. The calculated total flux of iodine atoms into the boundary layer at Mace Head from organic gaseous precursors was dominated by photolytic destruction of CH2I2. Photolysis of CH3I contributed less than 3%. The calculated peak flux of iodine atoms during the campaign coincided with the highest measured levels of iodine oxide radicals, as determined using Differential Optical Absorption Spectrometry (DOAS).

 

Segregation and Interpretation of Ozone and Carbon Monoxide Measurements by Air Mass Origin at Segregation and Interpretation of Ozone and Carbon Monoxide Measurements by Air Mass Origin at

Date added: 08/07/1997
Date modified: 07/23/2009
Filesize: 252.17 kB

Simmonds, PG, Seuring, S, Nickless, G, et al , Segregation and interpretation of ozone and carbon monoxide measurements by air mass origin at the TOR Station Mace Head, Ireland from 1987 to 1995, J ATMOS CHEM, 1997, Vol: 28, Pages: 45 - 59, ISSN: 0167-7764


Abstract


Three independent methods have been used to sort the ozone, carbon monoxide, and other radiatively important trace gases measured at Mace Head, Ireland, and thereby distinguish clean air masses transported over the North Atlantic from the more polluted air masses which have recently travelled from the European continent. Over the period April 1987-June 1995 the Northern Hemisphere surface ozone baseline concentrations exhibited a mean concentration of 34.8 ppb, with a small positive trend (+0.19 ppb yr-1), while the corresponding trend in air originating from the polluted European areas was negative (-0.39 ppb yr-1). Carbon monoxide measurements from March 1990 to December 1994 showed negative trends for both the unpolluted (-0.17 ppb yr-1) and polluted data (-13.6 ppb yr-1). Overall the continent of Europe was shown to be a small net sink of 2.6 ppb for all occasions when European air was transported to the North Atlantic.

 

Seasonal Variation of the Aerosol Light Scattering Coefficient in Marine Air of the Northeast Atlantic Seasonal Variation of the Aerosol Light Scattering Coefficient in Marine Air of the Northeast Atlantic

Date added: 03/12/2013
Date modified: 03/12/2013
Filesize: 677.22 kB

Aditya Vaishya, S. G. Jennings, and Colin O’Dowd. Seasonal Variation of the Aerosol Light Scattering Coefficient in Marine Air of the Northeast Atlantic, Advances in Meteorology, Volume 2011, Article ID 170490, doi:10.1155/2011/170490.


Abstract. Aerosol light scattering measurements were carried out using a TSI 3563 Nephelometer at the Mace Head Atmospheric Research Station, on the west coast of Ireland from year 2001–2010. A strong seasonal trend in the aerosol light scattering coefficient at 550nm (σscat), for clean marine air masses, is observed with a high σscat value, [average (geometric mean)] of 35.3Mm1(29.5Mm1), in January and a low σscat value of 13.7Mm1 (10.2Mm1), in July. This near threefold increase in the σscat value during the winter season is because of the large contribution of wind-speed generated sea-salt particles in the marine boundary layer. A high positive correlation coefficient of 0.82 was found between the percentage occurrence of relatively large A°ngstrom exponent (A° ) values (>1.2) and the percentage occurrence of lower σscat values (5–15Mm1) in the summer season. σscat and wind-speed have a high positive correlation coefficient of 0.88 whereas A° and wind-speed have a negative correlation coefficient of 0.89.values during the summer months indicate the dominance of sub-μm particles thus indicating the contribution of non-sea-salt sulphate and organics towards the σscat as these species show an enhanced concentration during the summer months.

 

Seasonal variation of the aerosol light scattering coefficient in marine air of the North-East Atlan Seasonal variation of the aerosol light scattering coefficient in marine air of the North-East Atlan

Date added: 11/17/2011
Date modified: 11/17/2011
Filesize: 677.22 kB

Vaishya, A., S.G. Jennings and C.D. O'Dowd, Seasonal variation of the aerosol light scattering coefficient in marine air of the North-East Atlantic, Adv. Met., Volume 2011, Article ID 170490, doi:10.1155/2011/170490, 2011.

 

  


Aerosol light scattering measurements were carried out using a TSI 3563 Nephelometer at the Mace Head Atmospheric Research Station, on the west coast of Ireland from year 2001–2010. A strong seasonal trend in the aerosol light scattering coefficient at 550nm (σscat), for clean marine air masses, is observed with a high σscat value, [average (geometric mean)] of 35.3Mm1 (29.5Mm1), in January and a low σscat value of 13.7Mm1 (10.2Mm1), in July. This near threefold increase in the σscat value during the winter season is because of the large contribution of wind-speed generated sea-salt particles in the marine boundary layer. A high positive correlation coefficient of 0.82 was found between the percentage occurrence of relatively large A° ngstro¨m exponent (A° ) values (>1.2) and the percentage occurrence of lower σscat values (5–15Mm1) in the summer season. σscat and wind-speed have a high positive correlation coefficient of 0.88 whereas °Aand wind-speed have a negative correlation coefficient of 0.89. °A values during the summer months indicate the dominance of sub-μm particles thus indicating the contribution of non-sea-salt sulphate and organics towards the σscat as these species show an enhanced concentration during the summer months

 

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