Journal Publications

Vaishya, A., S. G. Jennings, and C. O Dowd (2012), Wind-driven influences on aerosol light scattering in north-east Atlantic air, Geophys. Res. Lett., 39 , L05805, doi:10.1029/ 2011GL050556.

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Abstract. Ten years (2001–2010) of aerosol light-scattering measurements in N.E. Atlantic marine air are analysed to determine wind-speed related influences on scattering properties. The scattering coefficient and the backscattering coefficient dependency on wind speed (U) was determined for the winter (Low Biological Activity-LBA) and the summer seasons (High Biological Activity-HBA), and was found to be dependent on ~ U². In spite of having a U² dependency, scattering properties for the LBA-period are approximately twice those of the HBA-period. 96% of the LBA-HBA scattering difference can be explained by the combined effects of size distribution and refractive index differences while 70% of the scattering difference can be attributed to a difference in refractive index alone resulting from organic-matter enrichment during the HBA period. The 550 nm scattering coefficient was ~ 70 Mm^-1 for ~ 25 ms^-1 wind speeds, which is considerably higher than that encountered under polluted air masses in the same region. Indeed, Mulcahy et al. [2008] reported a high correlation between aerosol optical depth (AOD) and wind-speed with AOD values of 0.3–0.4 at moderately high wind speed. They found a power-law dependency between wind speed and AOD and suggested that sea spray contributed significantly to the direct radiative effect. O’Dowd et al. [1999] highlighted the preferential activation of sea salt nuclei over sulphate nuclei in marine clouds, while Ovadnevaite et al. [2011] found that even the water insoluble organic sea spray plumes have almost a 100% activation efficiency even at a low supersaturation of 0.2%, pointing to a significant role for sea spray in the direct radiative effect. While there have been many studies of aerosol lightscattering in remote locations and in marine air [Bodhaine, 1996; Parameswaran et al., 1998; Pereira et al., 2011], there have been few studies [e.g., Kleefeld et al., 2002] that have reported wind-dependent scattering dependency. The aim of present study is to establish a wind-speed scattering relationship for clean marine air masses for conditions representative of periods with high organic matter enrichment and periods with low organic matter enrichment.

 

O’Dowd, C., C. Scannell, J. Mulcahy & S. G. Jennings,   Wind Speed Influences on Marine Aerosol Optical Depth. Adv. in Meteorol., Article ID 830846,  2010. doi:10.1155/2010/830846, 2010.

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TheMulcahy (Mulcahy et al., 2008) power-law parameterization, derived at the coastal Atlantic stationMace Head, between clean marine aerosol optical depth (AOD) and wind speed is compared to open ocean MODIS-derived AOD versus wind speed. The reported AOD versus wind speed (U) was a function of 

∼U2. The open ocean MODIS-derived AOD at 550nm and 860nm wavelengths, while in good agreement with the general magnitude of the Mulcahy parameterization, follows a power-law with the exponent ranging from 0.72 to 2.47 for a wind speed range of 2–18ms−1. For the four cases examined, some MODIS cases underestimated AOD while other cases overestimated AOD relative to the Mulcahy scheme. Overall, the results from MODIS support the general power-law relationship of Mulcahy, although some linear cases were also encountered in the MODIS dataset. Deviations also arise between MODIS andMulcahy at higher wind speeds (>15ms−1), whereMODIS-derived AOD returns lower values as compared to Mulcahy. The results also support the suggestion than wind generated sea spray, under moderately high winds, can rival anthropogenic pollution plumes advecting out into marine environments with wind driven AOD contributing to AOD values approaching 0.3.

Gantt, B, N. Meskhidze, M.C. Facchini, M. Rinaldi, D. Ceburnis, C.D. O’Dowd, Wind speed dependent size-resolved parameterization for the organic enrichment of sea spray, Atmos. Chem. Phys., 11, 1–13, 2011, www.atmos-chem-phys.net/11/1/2011/doi:10.5194/acp-11-1-2011

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Abstract: For oceans to become a significant source of primary organic aerosol, sea spray must be highly enriched with organics relative to the bulk seawater.  We propose that organic enrichment at the air-sea interface, chemical composition of seawater, and the aerosol size are three main parameters controlling the organic mass fraction of sea spray aerosol (OM_ss).  To test this hypothesis, we developed a new marine primary organic aerosol emission function based on a conceptual relationship between the organic enrichment at the air-sea interface and surface wind speed.  The resulting parameterization is explored using aerosol chemical composition and surface wind speed from Atlantic and Pacific coastal stations, and satellite-derived ocean concentrations of chlorophyll-a, dissolved organic carbon, and particulate organic carbon.  Of all the parameters examined, a multi-variable logistic regression revealed that the combination of 10 meter wind speed and surface chlorophyll-a concentration ([Chl-a]) are the most consistent predictors of OM_ss.  This relationship, combined the published aerosol size dependence of OM_ss, resulted in a new parameterization for the organic carbon fraction of sea spray.  Global marine primary organic emission is investigated here by applying this newly-developed relationship to existing sea spray emission functions, satellite-derived [Chl-a], and modeled 10 meter winds.  Analysis of model simulations show that global annual submicron marine organic emission associated with sea spray is estimated to be from 2.8 to 5.6 Tg C yr^-1.  This study provides additional evidence that marine primary organic aerosols are a globally significant source of organics in the atmosphere.

 

Callaghan, A., G. de Leeuw, L. Cohen, C.D. O’Dowd, Oceanic Whitecap Coverage: Measurements from the North Atlantic, Geophys. Res. Letts., doi:10.1029/2008GL036165, 2008

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Abstract

 

Sea surface images obtained during the 2006 Marine Aerosol Production (MAP) campaign in the North East Atlantic were analysed for values of percentage whitecap coverage (W). Values of Ware presented for wind speeds up to circa 23 m s^-1. The W data were divided into two overlapping groups and a piecewise,  wind-speed-only parameterization of W is proposed that is valid for wind speeds between 3.70 m s^-1 and 23.09 m s^-1. Segregation of data points based upon a 2.5 hour wind history acted to decrease data scatter at wind speeds above approximately 9.25 m s^-1. At these wind speeds W values were greater for decreasing wind speeds than for increasing wind speeds. No clear wind history effect was observed at wind speeds below 9.25 m s^-1

Jennings. S.G, Wet properties affecting Atmospheric Aerosols, 1998, Atmospheric Particles, Pg 476-502, Wiley & Sons

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Abstract

 

The origin of atmospheric particles can be either anthropogenic (man-made) or natural. Primary particles are those which are emitted into the atmosphere as particles such as black carbon and organic particles in smoke plumes, soil dust particles, sea spray and volcanic particles, etc Secondary particles are formed from gas-to-particle coversion processes in the atmosphere- such as sulphates(from SO2), Nitreates (from (NOx) and secondary organics (from gaseous hydro-carbons)

Jennings. S.G, Wet properties affecting Atmospheric Aerosols, 1998, Atmospheric Particles, Pg 476-502, Wiley & Sons

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Abstract

 

The origin of atmospheric particles can be either anthropogenic (man-made) or natural. Primary particles are those which are emitted into the atmosphere as particles such as black carbon and organic particles in smoke plumes, soil dust particles, sea spray and volcanic particles, etc Secondary particles are formed from gas-to-particle coversion processes in the atmosphere- such as sulphates(from SO2), Nitreates (from (NOx) and secondary organics (from gaseous hydro-carbons)

Weather: Understanding rainfall,1971

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Abstract

Jennings, S.G., O'Dowd, C.D., Cooke, W.F., Sheridan, P.J. and Cachier, (1994). - Volatility of elemental carbon. Geophys. Res. Letts., 21, 1719 - 1722.

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Abstract

A volatility technique whereby aerosol particles are heated to the relatively high temperature of 860 °C is used to infer the presence of elemental carbon in polluted air masses in the vicinity of the west coast of Ireland. The volume of elemental carbon for submicrometre sized particles contained in the aerosol is estimated from the fall off in number concentration at a critical onset temperature of about 730 −735 °C, as also obtained for laboratory carbon ink aerosol. The technique permits determination of the elemental carbon volume percentage of the total fine aerosol volume, and an estimation of the abundance of elemental carbon contained within the black carbon fraction of the atmospheric aerosol. Supplementary black carbon mass concentration measurements were obtained using a thermal method and an aethalometer absorption method. The work suggests that elemental carbon can be identified using the volatility technique and that it can yield size-segregated information on the fraction of elemental carbon in atmospheric aerosol.

Jennings, S.G., O'Dowd, C.D., Cooke, W.F., Sheridan, P.J. and Cachier, (1994). - Volatility of elemental carbon. Geophys. Res. Letts., 21, 1719 - 1722.

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Abstract

A volatility technique whereby aerosol particles are heated to the relatively high temperature of 860 °C is used to infer the presence of elemental carbon in polluted air masses in the vicinity of the west coast of Ireland. The volume of elemental carbon for submicrometre sized particles contained in the aerosol is estimated from the fall off in number concentration at a critical onset temperature of about 730 −735 °C, as also obtained for laboratory carbon ink aerosol. The technique permits determination of the elemental carbon volume percentage of the total fine aerosol volume, and an estimation of the abundance of elemental carbon contained within the black carbon fraction of the atmospheric aerosol. Supplementary black carbon mass concentration measurements were obtained using a thermal method and an aethalometer absorption method. The work suggests that elemental carbon can be identified using the volatility technique and that it can yield size-segregated information on the fraction of elemental carbon in atmospheric aerosol.

Pinnick, R.G., Jennings, S.G., and Fernandez, G. (1987). - Volatility of aerosols in the arid south western United States. J. Atmos. Sci., 44, 391 - 400.

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Abstract

 

Volatile properties of aerosols at an isolated rural site in south-central New Mexico were measured with a light-scattering particle counter equipped with a temperature-controlled heated inlet. Intermittent measurements throughout a one-year period show that submicron particles are highly volatile and display temperature-fractionation characteristics of ammonium sulfate or bisulfate. It is estimated that 60-98 percent of the submicron aerosol fraction (by mass) is composed of these sulfates. Larger supermicron particles with radii greater than 0.4 micron, which are composed mostly of quartz and clay minerals of soil origin, are relatively involatile.

Jennings, S.G., and O'Dowd, C.D. (1990). - Volatility of aerosols at Mace Head on the west coast of Ireland. J. Geophys. Res., 95, 13,937 - 13,948.

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Abstract

Volatile properties of maritime and modified maritime aerosol were measured at the remote site at Mace Head (53°19′N, 9°54′W) on the west coast of Ireland, located on the eastern edge of the North Atlantic Ocean. The volatility measurements were made with a light-scattering counter equipped with a temperature-controlled heated inlet. The work extends the temperature range from 300°C to 850°C for the first time for aerosol volatility studies. Representative measurements made over the period of about a year show that the submicrometer particles with radius <0.2 μm are highly volatile for the maritime aerosol and show temperature fractionation features of ammonium sulfate (or ammonium bisulfate). It is estimated that 85–95% of this size fraction (by volume) is composed of these sulfates. For the higher temperatures, temperature-fractionation characteristics of sodium chloride are shown for the supermicron and also the submicron maritime particles. About 80% of the particle size interval of 0.3–1.5 μm radius is composed of sodium chloride. The temperature profile curves for the modified maritime aerosol, which has made a partial traverse overland, do not display definitive features characteristic of known atmospheric constituents such as ammonium sulfate or sodium chloride, but rather properties indicative of mixtures of these species with other unknown constituents. For both airmasses, between about 5% and 30% (by volume) of the aerosol particles remain involatile at least up to a temperature of 850°C.

R. G. Pinnick, D. L. Hoijelle, G. Fernandez, E. B. Stenmark, J. D. Lindberg, G. B. Hoidale, and S. G. Jennings,, "Vertical structure in atmospheric fog and haze and its effects on visible and infrared extinction," J. Atmos. Sci.35, 2020 (1978).

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Abstract

 

Vertical structure of the size distribution and number concentration of particulates in atmospheric fog and haze near Grafenwöhr, West Germany, were measured with a balloonborne light-scattering aerosol counter for periods spanning parts of eight days in February 1976. For haze (5 km visibility) conditions, little vertical variation is seen; but for low visibility (<1 km) fog conditions, significant vertical increases in concentration of droplets with radii larger than 4 μm are seen over the first 150 m altitude. For haze, the particle size distribution is approximated by a log-normal with geometric mean radius rg ≈ 0.2 μm and geometric standard deviation  σo ≈1.9. For fog, a bimodal distribution is found with a relative maximum for the larger particle mode at radii of 4 to 6 μm and corresponding values rg ≈ 5 m and σo ≈1.6; the smaller particle mode has values of rg ≈ 0.3 μm to rg ≈ 0.6 μm and σo  ≈1.8 to ≈2.5. Liquid water content values for haze and fog range from 10-4 to 0.45 g m-3. Extinction calculated from the particle size distributions shows an approximate 1/ λ wavelength dependence for haze conditions, but nearly neutral (wavelength independent) extinction for heavy fog. A correlation exists between calculated particulate extinction and calculated liquid water content, independent of particle size distribution, for the fogs and hues studied.

Pinnick, R. G.; Hoihjelle, D. L.; Stenmark, E. B.; Lindberg, James D., Vertical inhomogeneity in atmospheric fog and haze and its effects on infrared extinction, J. Opt. Soc. Am, Vol.68, Page 540

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Abstract

 

The presence of atmospheric fog and haze is important to radiative transfer in the atmosphere. For quantitative estimates of scattering and absorption by fod and haze particles, the size distribution is needed. Previously, fog and haze particulate size distributions have been measured by impaction techniques (Garland, 1971; Pilie, 1975; Krasikov and Chikirova, 1956; Kumai, 1973; low, 1975; May, 1961; barteneva and Polyakova, 1965; and Goodman, 1977), by collection of particles on spiderwebs (Arnulf et al., 1957), by a laser hologram camera (Kumkelm, 1971), and by light-scattering single particle counters (Eldridge, 1961; Laktionov, 1967). All of these techniques have serious limitations which restrict their usefulness and require measurements made with them to be regarded with caution. For example, impaction techniques involve laborious microsope measuremtn of droplets or droplet replicas, and corrections must be made to obtain true droplet size. Furthermore, impaction collection efficiencies must be applied to obtain relative particle concentrations.

 

In this article we present measurements of the size distribution of fog and haze particles made with a balloon-borne light-scattering single-particle counter, with emphasis on their effect on Infrared radiation. The primary advantages of using a light-scattering counter is that the measurement is donw in situ in real time, with minimal disturbance to the particles during measurement. Also, measurment of vertical structure is possible with this technique because a statistically significant size distribution measurement can be completed in a relatively short time (on the order of 1/2 minute), permitting a vertical upleg and lownleg to 200m altitude to be completed in 15 to 30 minutes. Measurements made during upleg and downleg portions of each tranverse show that temporal changes during such times scales were relatively small compared to vertical changes for most measurement periods.

Results from measurement of four haze and fog profiles presented here are typical of 19 profiles measured during February 1976 near Grafenwohr, a town located 100 km north of Nurnberg near the eastern border of West Germany. The local terrain consists of rollong hills and is partially forested; some of the land is tilled for farming.

Pinnick, R. G.; Jennings, S. G.; Chýlek, Petr; Auvermann, H. J., Verification of a Linear Relation between IR Extinction, Absorption and Liquid Water Content of Fogs., Journal of Atmospheric Sciences, vol. 36, Issue 8, pp.1577-1586

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Abstract

A linear relationship, independent of the form of the size-distribution, between extinction at wave-lengths around = 11 µm, absorption around = 3.8 and 9.5 µm, and liquid water content of atmospheric fogs has been verified using 341 droplet size distribution measurements made under a variety of meteorological conditions. The results suggest that integrated liquid water content along a path in fog can be determined from measurement of CO2 laser ( = 10.6 µm) transmission along the path, and that liquid water content at a particular point in fog can be inferred from in situ measurement of fog-droplet absorption with a deuterium fluoride laser ( = 3.8 µm) or a suitably tuned C02 laser ( = 9.5 µm) spectrophone.

Kleefeld C.; Geever M.; Jennings S.G.; Maring H.,Variations of CN number concentrations with respect to meteorological conditions at mace head, Ireland,Journal of Aerosol Science, Volume 29, Supplement 1, September 1998 , pp. 203-203(1)

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. B. Gillespie, S. G. Jennings, and J. D. Lindberg, "Use of an average complex refractive index in atmospheric propagation calculations," Appl. Opt. 17, 989-991 (1978)

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Abstract

 

In most atmospheric propagation calculation it is generally ssumed that atmospheric dust is composed of homogeneous spherical particles all with the same average complex refractive index and all distributed by the same size distribution. As pointed out by Bergstrom, it is perhaps more realisitc to assume that since diiferent optical constants and each component will have an associated size distribution characteristic of its production. In particular, the free carbon type particles and the soil derived particles should be different. Previous work in our laboratory  with commericallly available cascade impactors has shown that, for some minerals characteristic of the local envirorment, the imaginary refractive index of desert dust is a strong function of particle size.

Carpenter, L. J., A. C. Lewis, J. R. Hopkins, K. A. Read, I. D. Longley, and M. W. Gallagher (2004), Uptake of methanol to the North Atlantic Ocean surface, Global Biogeochem. Cycles, 18, GB4027, doi:10.1029/2004GB002294.

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Abstract

An anticorrelation between atmospheric methanol (CH₃OH) concentrations and wind speed and a positive correlation between dimethylsulphide (DMS) concentrations and wind speed have been observed at the coastal air monitoring site of Mace Head in Ireland, during a period of cyclonic activity in which the averaged surface wind speed changed substantially as a low-pressure system evolved over the northeast Atlantic. These observations suggest a net air-to-sea flux of CH₃OH. This conclusion is supported by the good agreement between the wind speed dependencies of the measured gas concentrations and theoretical predictions using wind-induced turbulent gas transfer velocities of DMS and CH₃OH calculated from a resistance model, embedded in a photochemical box model. For a wind speed of 8 m s⁻¹, an ocean deposition rate of methanol of between 0.02 and 0.33 cm s⁻¹ is calculated, with a best estimate of 0.09 cm s⁻¹, in good agreement with deposition rates used in global models and derived from atmospheric budgets. The large uncertainty in the calculated deposition rates is due almost entirely to the uncertainty in the degree of saturation of methanol in the surface ocean, highlighting the critical requirement for measurements of methanol in seawater. Owing to the dependence on wind speed, the deposition rates calculated showed substantial range and the calculated contribution of ocean deposition to total loss of CH₃OH (ocean uptake and gas phase OH oxidation) varied from approximately 20% to 60%.

 

Carpenter, L. J., A. C. Lewis, J. R. Hopkins, K. A. Read, I. D. Longley, and M. W. Gallagher (2004), Uptake of methanol to the North Atlantic Ocean surface, Global Biogeochem. Cycles, 18, GB4027, doi:10.1029/2004GB002294.

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Abstract

 

Methanol has an almost ubiquitous presence throughout the depth of the troposphere and has been identified as having an important effect on the atmospheric oxidative capacity, yet its global sources and sinks are not well known. Recent evaluations of the methanol budget conclude that a major uncertainty is whether the ocean is a net source or sink. During the North Atlantic Marine Boundary Layer Experiment (NAMBLEX) in July-August 2002, an anticorrelation between methanol concentrations and wind speed and a positive correlation between dimethylsulphide concentrations and wind speed was observed during a 3 day period of cyclonic activity in which the averaged surface wind speed changed substantially as a low pressure system evolved over the northeast Atlantic. The observations agreed well with theoretical predictions derived
assuming air-sea exchange according to the transfer velocity method, embedded in a zero dimensional box model. For the average wind speeds encountered, an irreversible ocean uptake rate of methanol of 8 x 10-7 s-1 was calculated, equivalent to a deposition rate of 0.08 cm s-1, in good agreement with deposition rates used in global models. However, owing to the dependence on wind speed, the uptake rates calculated
showed substantial range and the calculated contribution of ocean deposition to total destruction (uptake and OH destruction) varied from approximately 20% to 60%.

Albert , M. F. M. A., M. Schaap, A.M.M. Manders, C. Scannell, C.D. O’Dowd and G. de Leeuw, Uncertainties in the determination of global sub-micron marine organic

matter emissions, Atmos. Environ., 57, 289-300, 2012 http://dx.doi.org/10.1016/j.atmosenv.2012.04.009

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Abstract. Organic matter (OM) constitutes an important contribution to the composition of sub-micron sea-spray aerosol produced from biologically active waters. However, OM emission estimates vary by more than an order of magnitude. To estimate the uncertainties in the OM production estimates a sensitivity analysis has been performed in which various parameters have been varied. These include different sea-spray source functions, satellite-retrieved chlorophyll distributions, and a relationship correlating in situ organic mass measurements with satellite-retrieved chlorophyll data. The starting point was a baseline model from which the annual global emission of the water insoluble organic matter (WIOM) fraction in sea spray has been estimated to be 20.4 Tg. In this baseline the global WIOM emission is dominated by the contribution (80%) of the chlorophyll-poor regions (< 0.3 mg m^-3). Significant deviations from this estimate are introduced by the choice of the sea-spray source function and the assumed background organic mass fraction, each of which leads to an uncertainty of at least a factor of 2. In particular the chlorophyll-poor regions which dominate the WIOM contribution are strongly affected by the choice of the organic mass fraction parameterisation. The way the chlorophyll data are handled, such as different gap filling approaches, causes deviations in the OM emission that are in the order of 10% and is therefore of less importance. The present research indicates that special attention should be given to the low chlorophyll areas in e.g. the tropics, since there the parameterisations are most uncertain and at the same time these regions dominate total WIOM emissions.

 

J. M. MAKELA, P. AALTO, M.VAKEVA, K. HJ~MERI, I.K.KOPONEN, C.D.O'DOWD, M. KULMALA,ULTRAFINE PARTICLE SIZE DISTRIBUTIONS AT HYYTIP, LA BOREAL FOREST SITE AND AT A COASTAL SITE IN MACE HEAD,  J. Aerosol Sct. Vol. 3 I, Suppl. 1, pp S602- S603,2000

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Abstract

Number size distribution measurements in the submicron, and especially in the ultrafine size range, were carried out in the intensive field campaigns in connection with two EU projects BIOFOR (ENV4 - CT97 - 0405) and PARFORCE (ENV4-CT97- 0526). The studies in both projects were concentrated in finding the fundamental physico-chemical processes to cause the ambient particle formation phenomena that are observed at two continuous measurement sites (Makela et al, 1997, O'Dowd et al, 1999). The two sites in question are boreal forest site of Hyyti~il~i (SMEAR II) in '
Southern Finland and coastal site of Mace Head on the West coast of Ireland.

Dimmer, C.H., McCulloch, A., Simmonds, P.G., Nickless, G. Bassford, M.R. and Smythe-Wright, D. Tropospheric concentrations of the chlorinated solvents, tetrachloroethene, and trichloroethene, measured in the remote Northern Hemisphere, Atmospheric Environment, 35, 2001, 1171-1182.

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Abstract

A fully automated twin ECD gas chromatograph system with sample enriching adsorption-desorption primary stage was deployed on two field campaigns - Ny-Ålesund, Svalbard, Arctic Norway (July-September 1997), and the RRS Discovery CHAOS cruise of the northeast Atlantic (April-May 1998). Concentrations of an extensive set of halocarbons were detected at hourly intervals at pptv levels. We present the results obtained for the chlorinated solvents, tetrachloroethene (PCE) and trichloroethene (TCE). Average baseline PCE and TCE concentrations of 1.77 and 0.12 pptv, respectively, were recorded in Ny-Ålesund. During pollution incidences, concentrations rose to 5.61 (PCE) and 3.18 pptv (TCE). The cruise data showed average concentrations ranging from 4.26 (PCE) and 1.66 pptv (TCE) for air masses originating over the North Atlantic and Arctic open oceans, to maxima of 15.59 (PCE) and 17.51 pptv (TCE) for polluted air masses from Northern Europe. The data sets emphasise the difficulties in defining remote sites for background tropospheric halocarbon measurements, as Ny-Ålesund research station proved to be a source of tetrachloroethene. The data also suggest possible oceanic emissions of trichloroethene in the sub-tropical ocean.

 

Derwent, R. G., Simmonds, P. G., Manning, A. J., and Spain, T. G.: Trends over a 20-year
period from 1987–2007 in surface ozone at the atmospheric research station, Mace Head,
15 Ireland, Atmos. Environ., 41, 9091–9098, 2007.

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Abstract

Hourly measurements of baseline ozone at the Mace Head Atmospheric Research Station on the Atlantic Ocean coast of Ireland are observed when unpolluted air masses are advected to the station from across the North Atlantic Ocean. Monthly mean ozone mixing ratios in baseline air masses have risen steadily during the 1980s and 1990s reaching unprecedented levels during the early months of 1999. During the 2000s, baseline ozone mixing ratios have shown evidence of decline and stabilisation. Over the entire 20-year 1987-2007 period, the trend in annual baseline ozone has been +0.31±0.12(2-σ)ppbyear^-1 and is highly statistically significant. Trends have been highest in the spring months and lowest in the summer months, producing a significant increase in the amplitude of the seasonal cycle. Over the shorter 1995-2007 period, we demonstrate how the growth to peak in 1999 and the subsequent decline have been driven by boreal biomass burning events during 1998/1999 and 2002/2003. The 2000s have been characterised by relatively constant baseline ozone and CH₄ levels and these may be a reasonable guide to future prospects, at least in the short term.

 

Allen, D. J., P. Kasibhatla, A. M. Thompson, R. B. Rood, B. G. Doddridge, K. E. Pickering, R. D. Hudson, and S.-J. Lin (1996), Transport-induced interannual variability of carbon monoxide determined using a chemistry and transport model, J. Geophys. Res., 101(D22), 28,655–28,669.

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Abstract

Transport-induced interannual variability of carbon monoxide (CO) is studied during 1989–1993 using the Goddard chemistry and transport model (GCTM) driven by assimilated data. Seasonal changes in the latitudinal distribution of CO near the surface and at 500 hPa are captured by the model. The annual cycle of CO is reasonably well simulated at sites of widely varying character. Day to day fluctuations in CO due to synoptic waves are reproduced accurately at remote North Atlantic locations. By fixing the location and magnitude of chemical sources and sinks, the importance of transport-induced variability is investigated at CO-monitoring sites. Transport-induced variability can explain 1991–1993 decreases in CO at Mace Head, Ireland, and St. David's Head, Bermuda, as well as 1991–1993 increases in CO at Key Biscayne, Florida. Transport-induced variability does not explain decreases in CO at southern hemisphere locations. The model calculation explains 80–90% of interannual variability in seasonal CO residuals at Mace Head, St. David's Head, and Key Biscayne and at least 50% of variability in detrended seasonal residuals at Ascension Island and Guam. Upper tropospheric interannual variability during October is less than 8% in the GCTM. Exceptions occur off the western coast of South America, where mixing ratios are sensitive to the strength of an upper tropospheric high, and just north of Madagascar, where concentrations are influenced by the strength of offshore flow from Africa.

 

Forster, C., Wandinger, U., Wotawa, G., James, P., Mattis, I., Althausen, D., Simmonds, P., O'Doherty, S., Jennings, S. Gerard., Kleefeld, Christoph, Schneider, Johannes, Trickl, Thomas, Kreipl, Stephan, Jager, Horst, Stohl, Anreas. (2001). Transport of boreal forest fire emissions from Canada to Europe. J. Geophys. Res., 106, 22,887 - 22,906.

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Abstract

In August 1998, severe forest fires occurred in many parts of Canada, especially in the Northwest Territories. In the week from August 5 to 11, more than 1000 different fires burned >1 x 10⁶ ha of boreal forest, the highest 1-week sum ever reported throughout the 1990s. In this study we can unambigously show for the first time that these fires caused pronounced large-scale haze layers above Europe and that they influenced concentrations of carbon monoxide and other trace gases at the surface station Mace Head in Ireland over a period of weeks. Transport took place across several thousands of kilometers. An example of such an event, in which a pronounced aerosol layer was observed at an altitude of 3-6 km over Germany during August 1998, is investigated in detail. Backward trajectories ending at the measured aerosol layer are calculated and shown to have their origin in the forest fire region. Simulations with a particle dispersion model reveal how a substantial amount of forest fire emissions was transported across the Atlantic. The resulting aerosol lamina over Europe is captured well by the model. In addition, the model demonstrates that the forest fire emissions polluted large regions over Europe during the second half of August 1998. Surface measurements at Mace Head are compared to the model results for an anthropogenic and a forest fire carbon monoxide tracer, respectively. While wet deposition removed considerable amounts of aerosol during its transport, forest fire carbon monoxide reached Europe in copious amounts. It is estimated that during August 1998, 32%, 10%, and 58% of the carbon monoxide enhancement over the background level at Mace Head were caused by European and North American anthropogenic emissions and forest fire emissions, respectively.

Li, Q., et al. (2002), Transatlantic transport of pollution and its effects on surface ozone in Europe and North America, J. Geophys. Res., 107(D13), 4166, doi:10.1029/2001JD001422.

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Abstract

We examine the transatlantic transport of anthropogenic ozone and its impact on surface ozone in Europe and North America by using a 5-year (1993–1997) simulation with the GEOS-CHEM global three-dimensional model of tropospheric chemistry. Long-term time series of ozone and CO at Mace Head (Ireland) and Sable Island (Canada) are used to evaluate transatlantic transport in the model. North American anthropogenic emissions contribute on average 5 ppbv to surface ozone at Mace Head, and up to 10–20 ppbv during transatlantic transport events, which are forerunners of broader events in Europe. These events are associated with low-level westerly flow driven by an intense Icelandic low between Iceland and the British Isles. North American influence on ozone at Mace Head is strongly correlated with the North Atlantic Oscillation (NAO), implying that the NAO index can be used to forecast transatlantic transport of North American pollution to Europe. European anthropogenic emissions contribute on average less than 2 ppbv to surface ozone at Sable Island but up to 5–10 ppbv during transatlantic transport events. These events are associated with low-level easterly flow established by anomalous low pressure at 45°N over the North Atlantic. North American anthropogenic emissions enhance surface ozone in continental Europe by 2–4 ppbv on average in summer and by 5–10 ppbv during transatlantic transport events; transport in the boundary layer and subsidence from the free troposphere are both important mechanisms. We find in the model that 20% of the violations of the European Council ozone standard (55 ppbv, 8-hour average) in the summer of 1997 over Europe would not have occurred in the absence of anthropogenic emissions from North America. North American influence on surface ozone in Europe is particularly strong at the thresholds used for the European standards (55–65 ppbv).

Jennings, S.G., and Jones, C.D. (1977)- Tracking electrically charged puffs, as used in short range atmospheric diffusion investigations, by ground level electric field measurements. J. Electrostatics, 2, 367-373.

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Abstract

The use of ionized air as a tracer in short range atmospheric diffusion investigations raises the possibility of cloud location using electric field measurements. In this short communication a simple analysis is developed which enables the trajectory of a charged cloud to be ascertained from electric field measurements at three points at ground level (assuming the charge is known). Alternatively, if the charge is not known, it is shown that five-position electric field measurements are needed to find both its position and magnitude.

Arimoto, R., R. A. Duce, B. J. Ray, W. G. Ellis Jr., J. D. Cullen, and J. T. Merrill (1995), Trace elements in the atmosphere over the North Atlantic, J. Geophys. Res., 100(D1), 1199–1213.

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Abstract

The concentrations of trace elements in aerosol particles from the atmosphere over the North Atlantic Ocean were determined as part of a program designed to characterize the chemical climatology of the region. For these studies, which were part of the Atmosphere-Ocean Chemistry Experiment (AEROCE), 2 years of samples were collected at Tudor Hill, Bermuda (BTT), and at Ragged Point, Barbados (BAT); and 1 year of samples was collected at Mace Head, Ireland (MHT) and at the Izaña Observatory, Tenerife, Canary Islands (IZT). One major component of the aerosol was atmospheric dust, and the ranking for the median mineral dust concentrations as represented by aluminum was BAT > IZT > BTT > MHT. The Al concentrations at BAT, IZT, and BTT ranged over 4 orders of magnitude, i.e., from 0.001 to 10 μg m⁻³. At MHT the maximum dust concentrations were about a factor of 10 lower than at the other sites, but the lower end of the range in dust concentrations was similar at all sites. The mineral dust concentrations generally were highest in summer, and the flux of atmospheric dust was dominated by sources in North Africa. The elements showing clear enrichments over the concentrations expected from sea salt or crustal sources were I, Sb, Se, V, and Zn. At Izaña, which is in the free troposphere (elevation ∼2360 m), the concentrations of Se and I were much lower than at the boundary layer sites; this difference between sites most likely results from the marine emissions of these elements. The impact of pollution sources on trace element concentrations was evident at all sites but varied with season and location. The concentrations of elements originating from pollution sources generally were low at Barbados. Analyses of trace element ratios indicate that there are large-scale differences in the pollution emissions from North America versus those from Europe and Africa. Emissions from pyrometallurgical industries, steel and iron manufacturing, and possibly biomass burning are more evident in the atmospheric samples influenced by transport from Europe and Africa.

 

Hoell, C., C.D. O'Dowd, S.R. Osborne, and D.W. Johnson, Timescale Analysis of Marine Boundary Layer Aerosol Evolution: Lagrangian Case Studies Under Clean and Polluted Cloudy Conditions. Tellus, 52B,423-438, 2000

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Abstract

Significant changes were observed in the sub-micron aerosol size distribution during a clean and a polluted Lagrangian study of marine boundary layer (MBL) aerosol and meteorological evolution during ACE-2. These changes were accompanied by significant alterations in boundary layer meteorology and structure. The clean case (LAG1) shows a reduction in the fine mode aerosol from 1050 cm^-3 to 750 cm^-3 and an increase in the accumulation mode concentration from 76 cm^-3 to 162 cm^-3 over 26 h. Dominant meteorological features during the same period comprised a reduction in boundary layer height from 1500 m to 800 m and an increase in the surface layer wind speed from 5 m s^-1 to 15 m s^-1. A detailed time-scale analysis, based upon measured data and including processes such as coagulation, condensation, deposition, chemical processing, sea-salt flux and entrainment, suggests that the dominant loss process for fine mode aerosol is coagulation, while the enhancement of accumulation mode aerosol can be almost totally ascribed to enhanced sea-salt aerosol flux into the reduced mixed layer volume. Aerosol size distributions from the polluted Lagrangian (LAG2) indicated little growth in particle diameter, and both fine and accumulation mode were observed to decrease in concentration from 2700 cm^-3 to 1150 cm^-3 and from 670 cm^-3 to 430 cm^-3 in 26 h, respectively. Dilution with cleaner free tropospheric air as the boundary layer height increased from 500 m to >1000 m is suggested to be the primary factor relating to reduced aerosol concentrations in this case. To a smaller extent, coagulation and precipitation scavenging were calculated to be of some importance. For both Lagrangian case studies, meteorological changes, followed by physical aerosol-cloud interactions, appear to have the greatest influence on the MBL aerosol size distribution and number concentration over the given time-scale.

 

Temme C, Ebinghaus R, Einax JW, Steffen A, Schroeder WH. Time series analysis of long-term data sets of atmospheric mercury concentrations. Anal Bioanal Chem. 2004; 380:493–50

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Abstract

Different aspects and techniques of time series analysis were used to investigate long-term data sets of atmospheric mercury in the Northern Hemisphere. Two perennial time series from different latitudes with different seasonal behaviour were chosen: first, Mace Head on the west coast of Ireland (53°20′N, 9°54′W), representing Northern Hemispherical background conditions in Europe with no indications for so-called atmospheric mercury depletion events (AMDEs); and second, Alert, Canada (82°28′N, 62°30′W), showing strong AMDEs during Arctic springtime. Possible trends were extracted and forecasts were performed by using seasonal decomposition procedures, autoregressive integrated moving average (ARIMA) methods and exponential smoothing (ES) techniques. The application of time series analysis to environmental data is shown in respect of atmospheric long-term data sets, and selected advantages are discussed. Both time series have not shown any statistically significant temporal trend in the gaseous elemental mercury (GEM) concentrations since 1995, representing low Northern Hemispherical background concentrations of 1.72±0.09 ng m⁻³ (Mace Head) and 1.55±0.18 ng m⁻³ (Alert), respectively. The annual forecasts for the GEM concentrations in 2001 at Alert by two different techniques were in good agreement with the measured concentrations for this year.

 

O'DOWD C. D. ; SMITH M. H., The vertical structure of aerosol and its relationship to boundary-layer thermodynamics over the rural UK, Quarterly Journal of the Royal Meteorological Society, 1996, vol. 122 (B), no 536, pp. 1799-1814

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Abstract

The vertical structure of aerosol, covering sizes from 0.05-4 μm radius, was examined under conditions of subsidence during winter and summer over the rural UK. Under well-mixed boundary layer conditions, dry accumulation mode aerosol was found to be well mixed with height. During the winter campaigns, nocturnal cooling resulted in the development of a stable surface layer, typically 100 m in depth, within which the surface emitted pollutants became trapped leading to concentrations significantly greater than that observed in the mixed boundary layer above it. Under stable boundary-layer conditions, the aerosol and water vapour vertical profiles exhibited strong negative gradients with height and were indicative of suppressed turbulence associated with stable boundary-layer conditions. During summer, the boundary layer was normally decoupled and possessed two cloud layers: cumuli forming just below, and penetrating the surface-layer inversion; and stratocumulus occupying the region under the boundary-layer capping inversion. Aerosol profiles under decoupled conditions exhibited considerable variability with peak concentrations being observed in the vicinity of cloud edges. Average aerosol concentrations in the main boundary-layer ranged from 209-651 cm^-3 and 0.89-4.3 μm^-3 cm^-3 for dry number and volume respectively, whilst concentrations and volumetric loadings of 239-2430 cm^-3 and 1.1-13.5 μm³ were encountered in surface layers. The majority of the aerosol number and mass concentrations were almost exclusively derived from the size range 0.05-0.2 μm radius with mode radii often occurring at 0.1 μm or larger. By comparison, free tropospheric aerosol possessed typically an order of magnitude lower concentrations and mass with an associated mode radius of 0.05-0.06 μm or less.

 

Dall’Osto, R.M. Harrison, E. J.  Highwood, C. O’Dowd, D. Ceburnis, X. Querol and E. P. Achterberg, The variation of the mixing state of Saharan dust particles with atmospheric transport. Atmos. Env., doi:10.1016/j.atmosenv.2010.05.030, 2010,

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Mineral dust is an important aerosol species in the Earth

 

’s atmosphere and has a major source within North Africa, of which the Sahara forms the major part. Aerosol Time of Flight Mass Spectrometry (ATOFMS) is first used to determine the mixing state of dust particles collected from the land surface in the Saharan region, showing low abundance of species such as nitrate and sulphate internally mixed with the dust mineral matrix. These data are then compared with the ATOFMS single particle mass spectra of Saharan dust particles detected in the marine atmosphere in the vicinity of the Cape Verde islands, which are further compared with those from particles with longer atmospheric residence sampled at a coastal station at Mace Head, Ireland. Saharan dust particles collected near the Cape Verde  Islands showed increased internally mixed nitrate but no sulphate, whilst Saharan dust particles collected on the coast of Ireland showed a very high degree of internally mixed secondary species including nitrate, sulphate and methanesulphonate. This uptake of secondary species will change the pH  and hygroscopic properties of the aerosol dust and thus can influence the budgets of other reactive gases, as well as influencing the radiative properties of the particles and the availability of metals for

dissolution

Cape, J.N., J Methven and L.E Hudson, The use of trajectory cluster analysis to interpret trace gas measurements at Mace Head, Ireland, Atmos. Environ., 34, 3651-3663, 2000, (Ser. No. ACP088).

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Abstract

 

A first step in interpreting the wide variation in trace gas concentrations measured over time at a given site is to classify the data according to the prevailing weather conditions. In order to classify measurements made during two intensive field campaigns at Mace Head, on the west coast of Ireland, an objective method of assigning data to different weather types has been developed. Air-mass back trajectories calculated using winds from ECMWF analyses, arriving at the site in 1995-1997, were allocated to clusters based on a statistical analysis of the latitude, longitude and pressure of the trajectory at 12h intervals over 5 days. The robustness of the analysis was assessed by using an ensemble of back trajectories calculated for four points around Mace Head. Separate analyses were made for each of the 3 years, and for four 3-month periods. The use of these clusters in classifying ground-based ozone measurements at Mace Head is described, including the need to exclude data which have been influenced by local perturbations to the regional flow pattern, for example, by sea breezes. Even with a limited data set, based on 2 months of intensive field measurements in 1996 and 1997, there are statistically significant differences in ozone concentrations in air from the different clusters. The limitations of this type of analysis for classification and interpretation of ground-based chemistry measurements are discussed.

 

O’Dowd, C.D., P.P. Aalto, Y.J. Yoon, K. Hameri. The use the pulse height analyzer ultrafine condensation particle counter (PHA-UCPC) technique applied to sizing of nucleation mode particle of differing chemical composition. J. Aerosol. Sci. 2003. doi:10.1016/j.jaerosci.2003.08.003

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Abstract

A modified white-light pulse-height analyser (PHA) TSI 3025 ultra-fine condensation particle counter (UCPC) is often used to provide fast response of aerosol size distributions between 3 and 10 nm since there is a monotonic link between initial aerosol size and nucleated droplet final size. The use of the PHA-UCPC for sizing nucleation mode particles depends on the droplet nucleation in the condenser chamber being somewhat independent of particle composition. Laboratory characterization of the PHA-UCPC for a range of chemical compositions, thought to be involved in atmospheric aerosol nucleation and growth, are presented here. Ammonium sulphate, pinic acid, cis-pinonic acid, malonic acid and an iodine oxide were studied and their PHA-UCPC calibration kernels are presented. It was found that all species possessed significantly different PHA responses. The results suggest that, unless the nano-particle chemical composition is known, then the PHA-UCPC cannot be used for measurements of aerosol size distributions. However, the PHA-UCPC, if used in parallel with mobility size distribution measurements, can help elucidate nano-particle chemical composition. Using the combination of mobility size distributions and the PHA-UCPC response during a nucleation and growth event over the boreal forest indicates that new particle formation, in this region, is driven by condensation of organic vapours.

Seitz, K.,  J. Buxmann, D. Pöhler, T. Sommer, J. Tschritter, T. Neary, C. O’Dowd, and U. Platt,  The spatial distribution of the reactive iodine species IO from simultaneous active and passive DOAS observations, Atmos. Chem. Phys., 10, 2117–2128, 2010

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Abstract. :

We present investigations of the reactive iodine species (RIS) IO, OIO and I2 in a coastal region from a field  campaign simultaneously employing active long path differential optical absorption spectroscopy (LP-DOAS) as well as passive multi-axis differential optical absorption spectroscopy (MAX-DOAS). The campaign took place at the Martin Ryan Institute (MRI) in Carna, County Galway at the IrishWest Coast about 6 km south-east of the atmospheric research station Mace Head in summer 2007. In order to study the horizontal distribution of the trace gases of interest, we established two almost parallel active LP-DOAS light paths, the shorter of 1034m length just crossing the intertidal area, whereas the longer one of 3946m length also crossed open water during periods of low tide. In addition we operated two passive Mini-MAX-DOAS instruments with the same viewing direction. While neither OIO nor I2 could be unambiguously identified with any of the instruments, IO could be detected with active as well as passive DOAS. The IO column densities seen at both active LP-DOAS light paths are almost the same. Thus it can be concluded that coastal IO is almost exclusively located in the intertidal area, where we detected mixing ratios of up to 29±8.8 ppt (equivalent to pmol/mol). Nucleation events with particle concentrations of 106 cm−3 particles were observed each day correlating with high IO mixing ratios. Therefore we feel that our detected IO concentrations confirm the results of model studies, which state that in order to explain such particle bursts, IO mixing ratios of 50 to 100 ppt in so called “hot-spots” are required.

Laaksonen, A., M. Kulmala, C.D. O’Dowd, J. Joutsensaari, P. Vaattovaara, S. Mikkonen, K.E.J. Lehtinen, L. Sogacheva, M. Dal Maso, P. Aalto, T. Petäjä, A. Sogachev, Y. J. Yoon, H. Lihavainen, D. Nilsson, M. C. Facchini, F. Cavalli, S. Fuzzi, T. Hoffmann, F. Arnold, M. Hanke, K. Sellegri, B. Umann, W Junkermann, H. Coe, J. D. Allan, M. R. Alfarra, D.R. Worsnop, M.-L. Riekkola, T. Hyötyläinen and Y Viisanen., The role of VOC oxidation products in continental new particle formation, Atmos. Chem. And Phys. Discuss., 2007.

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Abstract

Aerosol physical and chemical properties and trace gas concentrations were measured during the QUEST field campaign in March–April, 2003, in Hyytiälä, Finland. Our aim was to understand the role of oxidation products of VOC's such as mono- and sesquiterpenes in atmospheric nucleation events. Particle chemical compositions were measured using the Aerodyne Aerosol Mass Spectrometer, and chemical compositions of aerosol samples collected with low-pressure impactors and a high volume sampler were analysed using a number of techniques. The results indicate that during and after new particle formation, all particles larger than 50 nm in diameter contained similar organic substances that are likely to be mono- and sesquiterpene oxidation products. The oxidation products identified in the high volume samples were shown to be mostly aldehydes. In order to study the composition of particles in the 10–50 nm range, we made use of Tandem Differential Mobility Analyzer results. We found that during nucleation events, both 10 and 50 nm particle growth factors due to uptake of ethanol vapour correlate strongly with gas-phase monoterpene oxidation product (MTOP) concentrations, indicating that the organic constituents of particles smaller than 50 nm in diameter are at least partly similar to those of larger particles. We furthermore showed that particle growth rates during the nucleation events are correlated with the gas-phase MTOP concentrations. This indicates that VOC oxidation products may have a key role in determining the spatial and temporal features of the nucleation events. This conclusion was supported by our aircraft measurements of new 3–10 nm particle concentrations, which showed that the nucleation event on 28 March 2003, started at the ground layer, i.e. near the VOC source, and evolved together with the mixed layer. Furthermore, no new particle formation was detected upwind away from the forest, above the frozen Gulf of Bothnia.

O'Dowd, C.D., J. Lowe, M.H. Smith and A.D. Kaye, The relative importance of sea-salt and nss-sulphate aerosol to the marine CCN population: An improved multi-component aerosol-droplet parameterisation. Q. J. Roy. Met. Soc., 125, 1295-1313. 1999

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Abstract

The effect of sub-cloud aerosol on cloud droplet concentration was explored over the north Atlantic and east Pacific under a variety of low and high wind speed conditions. A relationship of the form of D = 197(1-exp(-6.13 × 10^-3 * A)] was found to fit best the relationship between cloud droplet concentration (D; cm^-3) and sub-cloud aerosol concentration (A; cm^-3) under low to moderate wind conditions. A few noticeable deviations from this relationship were observed which occurred under moderate to high wind speed condition. Under these high wind conditions, sea-salt aerosol provided the primary source of cloud nuclei due to their higher nucleation activity and larger sizes, even under sulphate-rich conditions. Simple model simulations reveal that the activation of sea-salt nuclei suppresses the peak supersaturation reached in cloud, and thus inhibits the activation of smaller sulphate nuclei into cloud droplets. A multi-component aerosol-droplet parametrization for use in general circulation models is developed to allow prediction of cloud droplet concentration as a function of sea-salt and non-sea-salt-(nss) sulphate nuclei. The effects of enhancing an existing nss-sulphate cloud condensation nuclei (CCN) population with sea-salt nuclei are to reduce the number of cloud droplets activated under high (polluted) sulphate conditions and to increase the cloud droplet concentration under low (clean) sulphate conditions. The presence of sea-salt CCN reduces the influence of nss-sulphate CCN on cloud droplet concentrations, and thus is likely to reduce the predicted effect of nss-sulphate indirect radiative forcing.

 

Christoph Kleefeld, Colin O'Dowd, Sarah O'Reilly, S. Gerard Jennings, Pasi Alto, Edo, Becker, Gerard Kunz, Gerrit de Leeuw.The Relative Contribution of sub and super micron particles to aerosol light scattering in the marine boundary layer (MBL), J. Geophys. Res., 107, 10.1029/2000JD000262, 2002.

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Abstract

 

Measurements of the aerosol light scattering coefficient (ssp) at a wavelength of l = 550 nm were conducted at a coastal atmospheric research station in the east Atlantic Ocean during June 1999. Size distribution measurements between diameters of 3 nm and 40 mm (at ambient humidity) were used to derive scattering coefficients from Mie theory. The calculated scattering coefficients were about a factor of 7.4 higher than the measured scattering coefficients. The discrepancy was explained by a reduced cutoff of the sampling system at particle diameters between 6 and 8 mm, dependent on wind speed. The calculated aerosol scattering was about 1 order of magnitude higher than previously reported measurements in the MBL and is attributed to supermicrometer particles at sizes d > 10 mm dominating aerosol scattering. INDEX TERMS: 0305 Atmospheric Composition and Structure: Aerosols and particles (0345, 4801); 0360 Atmospheric Composition and Structure: Transmission and scattering of radiation; 3359 Meteorology and  Atmospheric Dynamics: Radiative processes; KEYWORDS: light scattering, sea-salt aerosol, marine boundary layer, particle size distribution, Mie theory

 

Pietikäinen, JP, D O'Donnell, C Teichmann, U Karstens, S Pfeifer, J Kazil, R Podzun, S Fiedler, H Kokkola, W Birmili, C O'Dowd, U Baltensperger, E Weingartner, R Gehrig, G Spindler, M Kulmala, J Feichter, D Jacob, A Laaksonen, The regional aerosol-climate model REMO-HAM, Geosci. Model Dev., 5, 1323-1339, doi: 10.5194, 2012.

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Abstract. REMO-HAM is a new regional aerosol-climate model. It is based on the REMO regional climate model and includes most of the major aerosol processes. The structure for aerosol is similar to the global aerosol-climate model ECHAM5-HAM, for example the aerosol module HAM is coupled with a two-moment stratiform cloud scheme. On the other hand, REMO-HAM does not include an online coupled aerosol-radiation nor a secondary organic aerosol module. In this work, we evaluate the model and compare the results against ECHAM5-HAM and measurements. Four different measurement sites were chosen for the comparison of total number concentrations, size distributions and gas phase sulphur dioxide concentrations: Hyyti¨al¨a in Finland, Melpitz in Germany, Mace Head in Ireland and Jungfraujoch in Switzerland. REMO-HAM is run with two different resolutions: 50×50 km²and 10×10 km². Based on our simulations, REMO-HAM is in reasonable agreement with the measured values. The differences in the total number concentrations between REMO-HAM and ECHAM5-HAM can be mainly explained by the difference in the nucleation mode. Since we did not use activation nor kinetic nucleation for the boundary layer, the total number concentrations are somewhat underestimated. From the meteorological point of view, REMO-HAM represents the precipitation fields and 2m temperature profile very well compared to measurement. Overall, we show that REMO-HAM is a functional aerosol-climate model, which will be used in further studies.

T.C. O'connor, AF Roddy, The production of Condensation Nuclei By Heated Wires, Journal de Recherches Atmospheriques Vol II 2e nos 2-3 pp 239-44

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Abstract

 

Investigations of the condensation nuclei produced by heated wires, particularly platinum, are described. There is a 'transient' type due to surface containation and a 'permanent' type which contain the material of the wire and are about 4 x 10^-7 cm in diameter. Nitrogen dioxide is also produced by the wires in the gaseous and not in the particulate form.

PJ Nolan & TC O Connor, The Photoelectric Nucleus Counter as Hygrometer, Geofisica Pura E Applicata - Milano Vol. 31 pp 32-36 (1955)

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Abstract

 

Hygrometric measurements on room air were made with a Nolan-Pollak nucleus counter from which the lining of blotting paper had been removed. The dew point can be determined from the critical overpressure for condensation on nuclei. Satisfactory agreement with the values given by a ventilated wet and dry blub hygrometer was obtained. The correction required is small since condensation occurs on ordinary atmospheric nuclei when the temperature is brought to about 0.3C below the dew point.

DERWENT R. G. ; SIMMONDS P. G.; GREALLY B. R.  ; O'DOHERTY S. ; MCCULLOCH A. ; MANNING A. ; REIMANN S. ; FOLINI D. ; VOLLMER M. K.   , The phase-in and phase-out of european emissions of HCFC-141b and HCFC-142b under the Montreal Protocol : Evidence from observations at Mace Head, Ireland and Jungfraujoch, Switzerland from 1994 to 2004, Atmospheric Environment , 41, 4, pg 757-767 (2007)

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Abstract

 

The mixing ratios of HCFC-141b (1,1-dichlorofluoroethane) and HCFC-142b (1-chloro-1,1-difluoroethane) have been rising steadily in baseline air at Mace Head, Ireland over the 10-year period from 1994 to 2004. These HCFCs are widely used replacements for the chlorofluorocarbons phased out under the Montreal Protocol and its subsequent amendments. Analysis of the HCFC content of regionally-polluted air arriving at Mace Head from the European continent shows that European emissions reached a peak during 2000-2001 and have declined subsequently, following the phase-out in their usage. European emissions of HCFC-141b have been further constrained by observations at the High-Alpine Jungfraujoch site. The reductions are consistent with the phase-out of HCFC production and use from the year 2001 onwards mandated by European regulations designed to exceed the requirements of the Montreal Protocol.

 

Ryall, D.B., R.G Derwent, A.J. Manning, A.L. Redington, J. Corden, W. Millington, P.G. Simmonds, S. O’Doherty, N. Carslaw and G.W. Fuller (2002), The origin of high particulate concentrations over the United Kingdom, March 2000, Atmos. Environ. 36, 1363-1378.

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Eckhardt, S., Stohl, A., Beirle, S., Spichtinger, N., James, P., Forster, C., Junker, C., Wagner, T., Platt, U., and Jennings, S. G.: The North Atlantic Oscillation controls air pollution transport to the Arctic, Atmos. Chem. Phys. Discuss., 3, 3222-3240, 2003

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Abstract

This paper studies the interannual variability of pollution pathways from northern hemisphere (NH) continents into the Arctic. Using a 1-year model simulation of the dispersion of passive tracers representative of anthropogenic emissions from NH continents, we show that the North Atlantic Oscillation (NAO) exerts a strong control on the pollution transport into the Arctic, particularly in winter and spring. For tracer lifetimes of 5 (30) days, surface concentrations in the Arctic winter are enhanced by about 70% (30%) during high phases of the NAO (in the following referred to as NAO⁺) compared to its low phases (NAO⁻). This is mainly due to great differences in the pathways of European pollution during NAO⁺ and NAO⁻ phases, respectively, but reinforced by North American pollution, which is also enhanced in the Arctic during NAO⁺ phases. In contrast, Asian pollution in the Arctic does not significantly depend on the NAO phase. The model results are confirmed using remotely-sensed NO₂ vertical atmospheric columns obtained from seven years of satellite measurements, which show enhanced northward NO₂ transport and reduced NO₂ outflow into the North Atlantic from Central Europe during NAO⁺ phases. Surface measurements of carbon monoxide (CO) and black carbon at high-latitude stations further corroborate the overall picture of enhanced Arctic pollution levels during NAO⁺ phases.

Eckhardt, S., Stohl, A., Beirle, S., Spichtinger, N., James, P., Forster, C., Junker, C., Wagner, T., Platt, U., and Jennings, S. G.: The North Atlantic Oscillation controls air pollution transport to the Arctic, Atmos. Chem. Phys., 3, 1769-1778, 2003.

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Abstract

This paper studies the interannual variability of pollution pathways from northern hemisphere (NH) continents into the Arctic. Using a 15-year model simulation of the dispersion of passive tracers representative of anthropogenic emissions from NH continents, we show that the North Atlantic Oscillation (NAO) exerts a strong control on the pollution transport into the Arctic, particularly in winter and spring. For tracer lifetimes of 5 (30) days, surface concentrations in the Arctic winter are enhanced by about 70% (30%) during high phases of the NAO (in the following referred to as NAO+) compared to its low phases (NAO-). This is mainly due to great differences in the pathways of European pollution during NAO+ and NAO- phases, respectively, but reinforced by North American pollution, which is also enhanced in the Arctic during NAO+ phases. In contrast, Asian pollution in the Arctic does not significantly depend on the NAO phase. The model results are confirmed using remotely-sensed NO2 vertical atmospheric columns obtained from seven years of satellite measurements, which show enhanced northward NO2 transport and reduced NO2 outflow into the North Atlantic from Central Europe during NAO+ phases. Surface measurements of carbon monoxide (CO) and black carbon at high-latitude stations further corroborate the overall picture of enhanced Arctic pollution levels during NAO+ phases

Heard, D. E., K. A. Read, J. Methven, S. Al-Haider, W. J. Bloss, G. P. Johnson, M. J. Pilling, P. W. Seakins, S. C. Smith, R. Sommariva, J. C. Stanton, T. J. Still, B. Brooks, G. De Leeuw, A. V. Jackson, J. B. McQuaid, R. Morgan, M. H. Smith, L. J. Carpenter, N. Carslaw, J. R. Hamilton, J. Hopkins, J. D. Lee, A. C. Lewis, R. M. Purvis, D. J. Wevill, N. Brough, T. Green, G. Mills, S. A. Penkett, J. M. C. Plane, A. Saiz-Lopez, D. Worton, P. S. Monks, Z. Fleming, A. R. Rickard, M. Alfarra, J. D. Allan, K. Bower, H. Coe, M. Cubison, M. Flynn, G. McFiggans, M. Gallagher, E. G. Norton, C. D. O'Dowd, J. Shillito, D. Topping, G. Vaughan, P. Williams, M. Bitter, S. M. Ball, R. L. Jones, I. M. Povey, S. O'Doherty, P. G. Simmonds, A. Allen, R. P. Kinnersley, D. C. S. Beddows, M. Dall'Osto, R. M. Harrison, R. J. Donovan, M. R. Heal, S. G. Jennings, C. Noone and G. Spain, The North Atlantic Marine Boundary Layer Experiment (NAMBLEX). Overview of the campaign held at Mace Head, Ireland, in summer 2002, Atmospheric Chemistry and Physics Discussions, Vol. 5, pp 12177-12254, 2005.

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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 NO_x 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, NO_x, NO_y, 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.

Heard, D. E., K. A. Read, J. Methven, S. Al-Haider, W. J. Bloss, G. P. Johnson, M. J. Pilling, P. W. Seakins, S. C. Smith, R. Sommariva, J. C. Stanton, T. J. Still, B. Brooks, G. De Leeuw, A. V. Jackson, J. B. McQuaid, R. Morgan, M. H. Smith, L. J. Carpenter, N. Carslaw, J. R. Hamilton, J. Hopkins, J. D. Lee, A. C. Lewis, R. M. Purvis, D. J. Wevill, N. Brough, T. Green, G. Mills, S. A. Penkett, J. M. C. Plane, A. Saiz-Lopez, D. Worton, P. S. Monks, Z. Fleming, A. R. Rickard, M. Alfarra, J. D. Allan, K. Bower, H. Coe, M. Cubison, M. Flynn, G. McFiggans, M. Gallagher, E. G. Norton, C. D. O'Dowd, J. Shillito, D. Topping, G. Vaughan, P. Williams, M. Bitter, S. M. Ball, R. L. Jones, I. M. Povey, S. O'Doherty, P. G. Simmonds, A. Allen, R. P. Kinnersley, D. C. S. Beddows, M. Dall'Osto, R. M. Harrison, R. J. Donovan, M. R. Heal, S. G. Jennings, C. Noone and G. Spain, The North Atlantic Marine Boundary Layer Experiment (NAMBLEX). Overview of the campaign held at Mace Head, Ireland, in summer 2002, Atmospheric Chemistry and Physics Discussions, Vol. 5, pp 12177-12254, 2005.

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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 NO_x 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, NO_x, NO_y, 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.

Heard, D. E., K. A. Read, J. Methven, S. Al-Haider, W. J. Bloss, G. P. Johnson, M. J. Pilling, P. W. Seakins, S. C. Smith, R. Sommariva, J. C. Stanton, T. J. Still, B. Brooks, G. De Leeuw, A. V. Jackson, J. B. McQuaid, R. Morgan, M. H. Smith, L. J. Carpenter, N. Carslaw, J. R. Hamilton, J. Hopkins, J. D. Lee, A. C. Lewis, R. M. Purvis, D. J. Wevill, N. Brough, T. Green, G. Mills, S. A. Penkett, J. M. C. Plane, A. Saiz-Lopez, D. Worton, P. S. Monks, Z. Fleming, A. R. Rickard, M. Alfarra, J. D. Allan, K. Bower, H. Coe, M. Cubison, M. Flynn, G. McFiggans, M. Gallagher, E. G. Norton, C. D. O'Dowd, J. Shillito, D. Topping, G. Vaughan, P. Williams, M. Bitter, S. M. Ball, R. L. Jones, I. M. Povey, S. O'Doherty, P. G. Simmonds, A. Allen, R. P. Kinnersley, D. C. S. Beddows, M. Dall'Osto, R. M. Harrison, R. J. Donovan, M. R. Heal, S. G. Jennings, C. Noone and G. Spain, The North Atlantic Marine Boundary Layer Experiment (NAMBLEX). Overview of the campaign held at Mace Head, Ireland, in summer 2002, Atmospheric Chemistry and Physics Discussions, Vol. 5, pp 12177-12254, 2005.

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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 NO_x 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, NO_x, NO_y, 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.

 

Allan B. J., G. McFiggans, J. M. C. Plane, H. Coe and G. G. McFadyen The Nitrate Radical in the Remote Marine Boundary Layer. J. Geophys. Res., 24191-24204, 2000.

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Abstract

The technique of differential optical absorption spectroscopy has been used to determine the nitrate radical (NO₃) concentration in the remote marine boundary layer. The instrument was deployed in campaigns at Mace Head on the west coast of Ireland and on the north coast of Tenerife. A comprehensive set of NO₃ measurements under a wide variety of conditions was obtained. For instance, nighttime NO₃ levels at Mace Head ranged from 1 to 5 ppt in the clean marine atmosphere and from 1 to 40 ppt in semipolluted continental air masses. The nightly averaged NO₃ lifetime varied from less than 2 min to 4 hours. At Tenerife, where there was less variability in conditions, nighttime NO₃ ranged from 1 to 20 ppt, with nightly averaged lifetimes between 4 and 34 min. A photochemical box model, fully constrained by measurements of species that control the formation and removal of NO₃, was then employed to determine the major loss mechanisms of the radical. This shows that NO₃ in the clean marine air masses is very sensitive to small increases in the concentrations of dimethyl sulphide (DMS) and nonmethane hydrocarbons and that the radical is rarely in chemical steady state. At Tenerife, 80 - 90% of NO₃ was removed by reaction with DMS. However, in continental air masses with little marine influence, indirect losses of NO₃ via dinitrogen pentoxide (N₂O₅) usually dominate. It appears that in much of the North Atlantic, NO₃ is a more efficient sink for DMS compared to the hydroxyl radical (OH) during the day.

 

Heard, D.E.The NAMBLEX field campaign 2002 [EGU04-A-03242].

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