High time-resolved aircraft data, concurrent surface measurements and air quality model simulations were explored to diagnose the processes influencing aerosol chemistry under the influence of lake-breeze circulations in a polluted region of southwestern Ontario, Canada. The analysis was based upon horizontal aircraft transects conducted at multiple altitudes across an entire lake-breeze circulation. Air mass boundaries due to lake-breeze fronts were identified in the aircraft meteorological and chemical data, which were consistent with the frontal locations determined from surface analyses. Observations and modelling support the interpretation of a lake-breeze circulation where pollutants were lofted at a lake-breeze front, transported in the synoptic flow, caught in a downdraft over the lake, and then confined by onshore flow. The detailed analysis led to the development of conceptual models that summarize the complex 3-D circulation patterns and their interaction with the synoptic flow. The identified air mass boundaries, the interpretation of the lake-breeze circulation, and the air parcel circulation time in the lake-breeze circulation (3.0 to 5.0 h) enabled formation rates of organic aerosol (OA/Delta CO) and SO42- to be determined. The formation rate for OA (relative to excess CO in ppmv) was found to be 11.6-19.4 mu g m(-3) ppmv(-1) h(-1) and the SO42- formation rate was 5.0-8.8 % h(-1). The formation rates are enhanced relative to regional background rates implying that lake-breeze circulations are an important dynamic in the formation of SO42- and secondary organic aerosol. The presence of cumulus clouds associated with the lake-breeze fronts suggests that these enhancements could be due to cloud processes. Additionally, the effective confinement of pollutants along the shoreline may have limited pollutant dilution leading to elevated oxidant concentrations.

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

This paper presents the results of laboratory studies on the condensational uptake of gaseous organic compounds in the exhaust of a light-duty gasoline engine onto preexisting sulfate and nitrate seed particles. Significant condensation of the gaseous organic compounds in the exhaust occurs onto these inorganic particles on a time scale of 25 min. The amount of condensed organic mass (COM) is proportional to the seed particle mass, suggesting that the uptake is due to dissolution determined by the equilibrium partitioning between gas phase and particles, not adsorption. The amount of dissolution in unit seed mass, S, decreases as a power function with increased dilution of the exhaust, ranging from 0.23 g g(-1) at a dilution ratio of 81, to 0.025 g g(-1) at a dilution ratio of 2230. It increases nonlinearly with increasing concentration of the total hydrocarbons in the gas phase (THC), rising from 0.12 g g(-1) to 0.26 g g(-1) for a CTHC increase of 1 to 18 mu g m(-3), suggesting that more organics are partitioned into the particles at higher gas phase concentrations. In terms of gas-particle partitioning, the condensational uptake of THC gases in gasoline engine exhaust can account for up to 30% of the total gas + particle THC. The organic mass spectrum of COM has the largest fragment at m/z 44, with mass ratios of mass fragments 43/44 and 57/44 at 0.59 and 2.91, much lower than those reported for gasoline engine primary organic aerosols. The mass fragment 44/total organic mass ratio of 0.097 indicates that COM contains large oxygenated components. By incorporating the present findings, regional air quality modelling results suggest that the condensational uptake of THC onto sulfate particles alone can be comparable to the primary particle mass under moderately polluted ambient conditions. These findings are important for modelling and regulating the air quality impacts of gasoline vehicular emissions.

Measurements made at a rural site in central Ontario during May-June 2007 are used to investigate the composition of organic aerosol (OA) downwind of an urban region. Observations of aerosol organic carbon and oxygen containing fragments from a high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) are combined with toluene to benzene ratios to estimate the relative importance of secondary organic aerosol (SOA) and primary organic aerosol (POA) to the total OA at the site during periods of significant urban influence. We estimate that SOA formed within 1-2 days of the anthropogenic source regions was 40-50% of the measured OA and that POA was 5-16% of the OA. The remaining 35-45% of the OA is assumed to have been present in the aerosol upwind of the source regions prior to entering the study domain as defined by trajectories and estimates of the potential photochemical aging time. The apportionment results were also compared to that of positive matrix factorization analysis. In addition, the measurements of the molar oxygen to carbon ratio (O/C) in the OA demonstrates that SOA becomes progressively more oxygenated with increasing photochemical age and at low total OA mass.

The Arctic climate is modulated, in part, by atmospheric aerosols that affect the distribution of radiant energy passing through the atmosphere. Aerosols affect the surface-atmosphere radiation balance directly through interactions with solar and terrestrial radiation and indirectly through interactions with cloud particles. Better quantification of the radiative forcing by different types of aerosol is needed to improve predictions of future climate. During April 2009, the airborne campaign Pan-Arctic Measurements and Arctic Regional Climate Model Inter-comparison Project (PAM-ARCMIP) was conducted. The mission was organized by Alfred Wegener Institute for Polar and Marine Research of Germany and utilized their research aircraft, Polar-5. The goal was to obtain a snapshot of surface and atmospheric conditions over the central Arctic prior to the onset of the melt season. Characterizing aerosols was one objective of the campaign. Standard Sun photometric procedures were adopted to quantify aerosol optical depth AOD, providing a three-dimensional view of the aerosol, which was primarily haze from anthropogenic sources. Independent, in situ measurements of particle size distribution and light extinction, derived from airborne lidar, are used to corroborate inferences made using the AOD results. During April 2009, from the European to the Alaskan Arctic, from sub-Arctic latitudes to near the pole, the atmosphere was variably hazy with total column AOD at 500 nm ranging from similar to 0.12 to >0.35, values that are anomalously high compared with previous years. The haze, transported primarily from Eurasian industrial regions, was concentrated within and just above the surface-based temperature inversion layer. Extinction, as measured using an onboard lidar system, was also greatest at low levels, where particles tended to be slightly larger than at upper levels. Black carbon (BC) (soot) was observed at all levels sampled, but at moderate to low concentrations compared with historical records. BC was highest near the North Pole, suggesting there had been an accumulation of soot within the Arctic vortex. Few, optically thick elevated aerosol layers were observed along the flight track, although independent lidar observations reveal evidence of the passage of volcanic plumes, which may have contributed to abnormally high values of AOD above 4 km. Enhanced opacity at higher altitudes during the campaign is attributed to an accumulation of industrial pollutants in the upper troposphere in combination with volcanic aerosol resulting from the March-April 2009 eruptions of Mount Redoubt in Alaska. The presence of Arctic haze during April 2009 is estimated to have reduced the net shortwave irradiance by similar to 2-5 W m(-2), resulting in a slight cooling of the surface.

Ultrafine particle (UFP) number and size distributions were simultaneously measured at five urban and rural sites during the summer of 2007 in Ontario, Canada as part of the Border Air Quality and Meteorology Study (BAQS-Met 2007). Particle formation and growth events at these five sites were classified based on their strength and persistence as well as the variation in geometric mean diameter. Regional nucleation and growth events and local short-lived strong nucleation events were frequently observed at the near-border rural sites, upwind of industrial sources. Surprisingly, the particle number concentrations at one of these sites were higher than the concentrations at a downtown site in a major city, despite its high traffic density. Regional nucleation and growth events were favored during intense solar irradiance and in less polluted cooler drier air. The most distinctive regional particle nucleation and growth event during the campaign was observed simultaneously at all five sites, which were up to 350 km apart. Although the ultrafine particle concentrations and size distributions generally were spatially heterogeneous across the region, a more uniform spatial distribution of UFP across the five areas was observed during this regional nucleation event. Thus, nucleation events can cover large regions, contributing to the burden of UFP in cities and potentially to the associated health impacts on urban populations. Local short-lived nucleation events at the three near-border sites during this summer three-week campaign were associated with high SO2, which likely originated from US and Canadian industrial sources. Hence, particle formation in southwestern Ontario appears to often be related to anthropogenic gaseous emissions but biogenic emissions at times also contribute. Longer-term studies are needed to help resolve the relative contributions of anthropogenic and biogenic emissions to nucleation and growth in this region.

Submicron particles collected at Whistler, British Columbia, at 1020 m a.s.l. during May and June 2008 on Teflon filters were analyzed by Fourier transform infrared (FTIR) and X-ray fluorescence (XRF) techniques for organic functional groups (OFG) and elemental composition. Organic mass (OM) concentrations ranged from less than 0.5 to 3.1 mu g m(-3), with a project mean and standard deviation of 1.3 +/- 1.0 mu g m(-3) and 0.21 +/- 0.16 mu g m(-3) for OM and sulfate, respectively. On average, organic hydroxyl, alkane, and carboxylic acid groups represented 34%, 33%, and 23% of OM, respectively. Ketone, amine and organosulfate groups constituted 6%, 5%, and <1% of the average organic aerosol composition, respectively. Measurements of volatile organic compounds (VOC), including isoprene and monoterpenes from biogenic VOC (BVOC) emissions and their oxidation products (methyl-vinylketone/methacrolein, MVK/MACR), were made using co-located proton transfer reaction mass spectrometry (PTR-MS). We present chemically-specific evidence of OFG associated with BVOC emissions. Positive matrix factorization (PMF) analysis attributed 65% of the campaign OM to biogenic sources, based on the correlations of one factor to monoterpenes and MVK/MACR. The remaining fraction was attributed to anthropogenic sources based on a correlation to sulfate. The functional group composition of the biogenic factor (consisting of 32% alkane, 25% carboxylic acid, 21% organic hydroxyl, 16% ketone, and 6% amine groups) was similar to that of secondary organic aerosol (SOA) reported from the oxidation of BVOCs in laboratory chamber studies, providing evidence that the magnitude and chemical composition of biogenic SOA simulated in the laboratory is similar to that found in actual atmospheric conditions. The biogenic factor OM is also correlated to dust elements, indicating that dust may act as a non-acidic SOA sink. This role is supported by the organic functional group composition and morphology of single particles, which were analyzed by scanning transmission X-ray microscopy near edge X-ray absorption fine structure (STXM-NEXAFS).

Ambient particulate matter (PM) samples were collected on quartz filters at a rural site in central Ontario during an intensive study in 2007. The concentrations of organic carbon (OC), pyrolysis organic carbon (POC), and elemental carbon (EC) were determined by thermal analysis. The concentrations are compared to the organic aerosol mass concentration (OM) measured with an Aerodyne C-ToF Aerosol Mass Spectrometer (AMS) and to the particle absorption coefficient (b(asp)) obtained from a Radiance Research Particle Soot Absorption Photometer (PSAP). The total organic mass to organic carbon ratios (OM/OC) and specific attenuation coefficients (SAC=b(asp)/EC) are derived. Proportionality of the POC mass with the oxygen mass in the aerosols estimated from the AMS offers a potential means to estimate OM/OC from thermal measurements only. The mean SAC for the study is 3.8 +/- 0.3 m(2) g(-1). It is found that the SAC is independent of or decrease with increasing particle mass loading, depending on whether or not the data are separated between aerosols dominated by more recent anthropogenic input and aerosols dominated by longer residence time or biogenic components. There is no evidence to support an enhancement of light absorption by the condensation of secondary material to particles, suggesting that present model simulations built on such an assumption may overestimate atmospheric warming by BC.

1-Chloro-2,2-bis(4-chlorophenyl)ethene(p,p'-DDMU),a metabolite of either 1,1-dichloro-2,2-bis(4-chlorophenyl)ethane (pp'-DDD) or 1,1-dichloro-2,2-bis(4-chlorophenyl)ethene (p,p'-DDE), which is degraded from 1,1,1-trichloro-2,2-bis(4-chlorophenyl)ethane (p,p'-DDT), was detected in a variety of environmental matrices of the Pearl River Delta (PRD), South China, including fish, fish feeds, semidigested fish stomach contents, marine surface sediment, surface soil, atmospheric gaseous phase, and particulates, rainwater, and coastal rainwater. For fish species,the concentrations of p,p'-DDMU were significantly higher in farmed fish than in marine wild fish, with the highest value obtained in seawater farmed fish species (mean/median values of 262/173 ng/g lipid). The relative abundance of p,p'-DDMU to total DDTs (sum of o,p'-and p,p'-DDT, DDD, and DDE) was higher in samples of marine origin (similar to 5%) than in those of terrestrial origin (similar to 2%). Because p,p'-DDD was considerably abundant in all samples and a negative linear correlation was found between p,p'-DDD/(p,p'-DDD + p,p'-DDE) and p,p'-DDMU/DDTs in the marine sediments (r(2) = 0.73) and seawater farmed fish (r(2) = 0.29) under investigation, it is possible that DDMU was partially dehydrochlorinated from DDD in the environment of the PRD. A fugacity-based assessment suggested that p,p'-DDMU is likely to transport from sediment to seawater and then to air and from soil to air. The ubiquity of p,p'-DDMU in the PRD indicates that it may also be widespread worldwide particularly in countries with large amounts of DDT used currently and/or historically. Given the potential risk of p,p'-DDMU to human health, more efforts should be directed toward to this previously overlooked contaminant.

Ninety-six riverine runoff samples collected at eight major outlets in the Pearl River Delta (PRD), South China, during 2005-2006 were analyzed for 17 brominated diphenyl ether (BDE) congeners (defined as Sigma 17PBDE). Fourteen and 15 congeners were detected, respectively, in the dissolved and particulate phases. These data were further used to elucidate the partitioning behavior of BIDE congeners in riverine runoff. Several related fate processes, i.e. air-water exchange. dry and wet deposition, degradation, and sedimentation, within the Pearl River Estuary (PRE), were examined to estimate the inputs of Sigma 10PBDE (sum of the target BDE congeners, BDE-28, -47, -66, -85, -99, -100, -138, -153, -154, and -183) and BDE-209 from the PRD to the coastal ocean based on mass balance considerations. The results showed that annual outflows of Sigma 10PBDE and BDE-209 were estimated at 126 and 940 kg/year, respectively from the Besides sedimentation and degradation, the majority of Sigma 10PBDE and BDE-209 PRE to coastal ocean. discharged into the PRE via riverine runoff was transported to the coastal ocean. (C) 2009 Elsevier Ltd. All rights reserved.

On the basis of a one-year (from October 2006 to September 2007) sampling campaign, 34 air samples and 23 bulk precipitation samples were collected in the Pearl River Delta (PRO) in southern China and analyzed for polybrominated diphenyl ethers (PBDEs). Fifteen tri- to deca-BDE congeners (sum of which is defined as Sigma 15PBDE) were detected in more than 70% of the samples. In three urban-rural regions, Sigma 15PBDE concentrations ranged from 77 to 372 pg/m(3) in air (particulate + vapor) and 1.98 to 15.5 ng/L in rain (particle + dissolved) from Dongguan, from 195 to 1450 pg/m(3) in air and 4.71 to 17.2 ng/L in rain from Shunde, and from 23.7 to 148 ng/L in rain from Guangzhou. Among the BDE congeners, BDE-209 was the predominant component Linear correlations between the gas-particle partition coefficients (K-p) and the subcooled vapor pressures (P) of individual BDE congeners were observed for both the wet and dry seasons, but the slopes (-0.572 to -0.525) of the fitted equations all substantially deviated from equilibrium condition (slope = -1). The total washout ratio by bulk rainfalls was determined to be 2 x 10(3) for tri-BDEs and 6 x 10(4) for BDE-209. The estimated annual dry and wet depositional rates were 6720 and 2460 kg/yr, respectively, for BDE-209, and 7270 and 2940 kg/yr for Sigma 15PBDE in the PRO, indicating a dominant pathway for PBDEs input into the PRD soil and aquatic environments.

In Canada approximately 45% of ammonia (NH(3)) emissions are attributed to dairy and beef cattle industries. The present study focused on NH(3) emissions from a beef feedlot with a one-time capacity of 17,220 head. The aim was to improve the Canadian NH(3) emission inventories and air quality forecasting capabilities. A Cessna 207. equipped with a fast-response NH(3)/NO(y) detector and a quadrupole aerosol mass spectrometer, was flown in a grid pattern covering an area of 8 x 8 km centered on a feedlot (800 x 800 m) at altitudes ranging from 30 to 300 m above ground. Stationary ground measurements of NH(3) concentration and turbulence parameters were made downwind of the feedlot. Three flights were conducted under varying meteorological conditions, ranging from very calm to windy with near-neutral stratification. NH(3) mixing ratios up to 100 ppbv were recorded on the calm day, up to 300 m above ground. An average feedlot NH(3) emission rate of 76 +/- 4 mu g m(-2) s(-1) (equivalent to 10.2 g head(-1) h(-1)) was estimated. Characteristics of the measured NH(3) plume were compared to those predicted by a Lagrangian dispersion model. The spatially integrated pattern of NH(3) concentrations predicted and measured agreed but the measured was often more complex than the predicted spatial distribution. The study suggests that the export of NH(3) through advection accounted for about 90% of the emissions from the feedlot, chemical transformation was insignificant, and dry deposition accounted for the remaining 10%. Crown Copyright (C) 2009 Published by Elsevier Ltd. All rights reserved.

The effects of the accuracy of major-point source emissions input data on the predictions of a regional air-quality model (AURAMS) were investigated through a series of scenario simulations. The model domain and time period were chosen to correspond to that of PrAIRie2005, an air-quality field study with airborne and ground-based mobile measurement platforms that took place between August 12th and September 7th, 2005, over the city of Edmonton, Alberta, Canada. The emissions data from standard sources for three coal-fired power-plants located west (typically upwind) of the city were compared to the continuous emissions monitoring system (CEMS) taking place at the time of the study - the latter showed that the original emissions inventory data considerably overestimated NOx, SO2, and primary particulate emissions during the study period. Further field investigation (stack sampling) in the fall of 2006 showed that the measured primary particle size distribution and chemical speciation for the emissions were strikingly different from the distribution and speciation originally used in the model. The measured emissions were used to scale existing emissions data in accord with the CEMS and in-stack measurements. The effects of these improvements to the emissions data were examined sequentially in nested AURAMS simulations (finest horizontal resolution 3 km), and were compared to airborne aerosol mass spectrometer (Aerodyne AMS) measurements of particle sulphate, and particle distributions from an airborne passive cavity aerosol spectrometer probe (PCASP). The emissions of SO2 had the greatest impact on predicted PM, sulphate, while the primary particle size distribution and chemical speciation had a smaller role. The revised emissions data greatly improved the comparisons between observations and model values, though over-predictions of fine-mode sulphate still occur near the power-plants, with the use of the revised emissions data. The modified emissions also had a significant impact on the larger particles of the particulate matter, with more primary PM in sizes greater than 1 mu m diameter than had previously been estimated, and higher large particle concentrations close to the power-plants. Crown Copyright (C) 2008 Published by Elsevier Ltd. All rights reserved.

Several cases of aerosol plumes resulting from trans-Pacific transport were observed between 2 km and 5.3 km at Whistler, BC from 22 April 2006 to 15 May 2006. The fine particle (<1 mu m) chemical composition of most of the plumes was dominated by sulphate that ranged from 1-5 mu g m(-3) as measured with a Quadrapole Aerosol Mass Spectrometer (Q-AMS). Coarse particles (>1 mu m) were enhanced in all sulphate plumes. Fine particle organic mass concentrations were relatively low in most plumes and were nominally anti-correlated with the increases in the number concentrations of coarse particles. The ion chemistry of coarse particles sampled at Whistler Peak was dominated by calcium, sodium, nitrate, sulphate and formate. Scanning transmission X-ray microscopy of coarse particles sampled from the NCAR C-130 aircraft relatively close to Whistler indicated carbonate, potassium and organic functional groups, in particular the carboxyl group. Asian plumes reaching Whistler, BC during the INTEX-B study were not only significantly reduced of fine particle organic material, but organic compounds were attached to coarse particles in significant quantities. Suspension of dust with deposited organic material and scavenging of organic materials by dust near anthropogenic sources are suggested, and if any secondary organic aerosol (SOA) was formed during transport from Asian source regions across the Pacific it was principally associated with the coarse particles. An average of profiles indicates that trans-Pacific transport between 2 and 5 km during this period increased ozone by about 10 ppbv and fine particle sulphate by 0.2-0.5 mu g m(-3). The mean sizes of the fine particles in the sulphate plumes were larger when dust particles were present and smaller when the fine particle organic mass concentration was larger and dust was absent. The coarse particles of dust act to accumulate sulphate, nitrate and organic material in larger particles, diminishing the role of these compounds in indirect radiative forcing, but potentially enhancing their roles in direct radiative forcing.

An Aerodyne High Resolution Time-of-Flight Aerosol Mass Spectrometer (HR-ToF-AMS) was deployed at the peak of Whistler Mountain (2182 m above sea level), British Columbia, from 19 April to 16 May 2006, as part of the Intercontinental Chemical Transport Experiment Phase B (INTEX-B) campaign. The mass concentrations and size distributions of non-refractory submicron particle (NR-PM1) species (i.e., sulfate, nitrate, ammonium, chloride, and organics) were measured in situ at 10-min time resolution. The HR-ToF-AMS results agreed well with collocated measurements. The average concentration of non-refractory submicron particulate matter (NR-PM1; 1.9 mu g m(-3)) is similar to those observed at other remote, high elevation sites in North America. Episodes of enhanced aerosol loadings were observed, due to influences of regional and trans-Pacific transport of air pollution. Organics and sulfate were the dominant species, on average accounting for 55% and 30%, respectively, of the NR-PM1 mass. The average size distributions of sulfate and ammonium both showed an accumulation mode peaking at similar to 500 nm in vacuum aerodynamic diameter (D-va) while those of organic aerosol (OA) and nitrate peaked at similar to 300 nm. The size differences suggested that sulfate and OA were mostly present in external mixtures from different source origins. We also quantitatively determined the elemental composition of OA using the high resolution mass spectra. Overall, OA at Whistler Peak was highly oxygenated, with an average organic-mass-to-organic-carbon ratio (OM/OC) of 2.28 +/- 0.23 and an atomic ratio of oxygen-to-carbon (O/C) of 0.83 +/- 0.17. The nominal formula for OA was C1H1.66N0.03O0.83 for the entire study. Two significant trans-Pacific dust events originated from Asia were observed at Whistler Peak during this study. While both events were characterized with significant enhancements of coarse mode particles and mineral contents, the composition and characteristics of NR-PM1 were significantly different between them. One trans-Pacific event occurred on 15 May 2006, during which ammonium sulfate contributed >90% of the total NR-PM1 mass. This event was followed by a high OA episode likely associated with regional emissions. In total, three enhanced regional OA events, each of which lasted 2 3 days, were observed during this study. In contrast to the two dust events, the regional OA events were generally characterized with higher OA/sulfate ratio, less oxidized OA, and lower OM/OC ratio.

The role of clouds in the transport and transformation of tropospheric pollutants was investigated through airborne measurements made out of Cleveland, Ohio, from 21 July to 18 August 2004, as part of the International Consortium for Atmospheric Research on Transport and Transformation 2004 program. Observations of gas-phase nitrate, size-resolved particulate nitrate, cloud water nitrate, and size-distributed cloud residual nitrate are used to examine changes in the partitioning of nitrate from precloud to postcloud as a function of particle size. The [NO3-]/[SO42-] ratio was highest in the bulk cloud water and higher in the cloud droplet residuals compared with the below-cloud aerosols. Most of the nitrate entered the cloud water as HNO3, and in 30% of 43 size distributions examined, the nitrate in the cloud droplets was found in residual particle sizes smaller than those of sulfate. Simulations from a trace gas-aerosol-cloud parcel model show that this size difference results from differences in the processes by which nitrate and sulfate enter cloud water. The transfer of HNO3 to cloud droplets is governed primarily by gas-phase mass transfer to the droplets, leading to greater accumulation in the smaller, more numerous droplets with higher total surface area. In contrast, much of the sulfate in the cloud water is the result of nucleation scavenging, which distributes the sulfate mass toward slightly larger sizes. The extent of separation between nitrate and sulfate is dependent on the cloud base sulfate size distribution and the factors that govern both HNO3 and SO2 uptake, with subsequent S(IV) oxidation.

Air borne measurements carried out in the summer of 2004 in the lower Great Lakes region as part of the ICARTT 2004 study are used to examine the effects of clouds on the carbonyls in the atmosphere. Concentrations of seven carbonyl species in bulk cloudwater samples were measured with concurrent gas phase HCHO measurements. In the cloudwater, the most abundant carbonyl was HCHO with a median value of 11.9 mu mol L-1, followed by acetaldehyde (4.3 mu mol L-1), acetone (1.9 mu mol L-1), pentanal (1.4 mu mol L-1), benzaldehyde (0.5 mu mol L-1), butanal (0.4 mu mol L-1), and propanal (0.2 mu mol L-1). The relative abundance of propanal to acetaldehyde in the cloudwater was substantially lower than estimates from primary emissions. The cloudwater abundance of HCHO relative to the sum of the other carbonyls was found to increase with altitude in the clouds that penetrated the boundary layer. During most flights, the total in-cloud HCHOt (cloudwater + interstitial gas phase) was similar to cloud base HCHOg, suggesting that HCHO was distributed between the two phases through partitioning governed by Henry's law. However, during at least one flight, HCHOt was significantly depleted in the cloud. Finally, the equilibrium gas phase mixing ratios predicted from the cloudwater for all carbonyls but HCHO were much higher than previously measured in the gas phase.

Atmospheric particles were collected in the high Arctic at Alert during winter (February) and spring (April-May) and were subjected to stable carbon isotopic (delta C-13) measurements to better understand the source of carbonaceous aerosols. The mean delta C-13 values of aerosol total carbon (TC) were observed to increase from winter (-25.7 +/- 0.7%) to spring (-23.7 +/- 0.8%). A strong correlation (r(2) = 0.92, p < 0.001) was found between the delta C-13 values and Na+/TC ratios. The increased delta C-13 values were most likely explained by an enhanced sea-to-air emission of marine organic matter to the high Arctic and also by a decreased atmospheric transport of anthropogenic carbon from the midlatitudes. The backward trajectory analysis together with inorganic ion analysis indicated that spring aerosols were more affected by the Arctic Ocean than winter aerosols that were mainly derived from the primary pollutants emitted in the midlatitudes. On the basis of the delta C-13 values and Na+/TC ratios, contribution of marine organic matter to aerosol TC was estimated to be 45% in late spring. The enhanced sea-to-air emission of marine organic carbon is probably linked with a melting of sea ice, expansion of leads, and increased biological activity in the Arctic Ocean after the polar sunrise in spring.

The PrAIRie2005 campaign took place in the summer of 2005 in the city of Edmonton, Alberta. The measurement campaign was designed and led by air-quality modellers with the scientific objective of determining the extent to which air pollution events in the city are the result of locally emissions versus long-range transport. A nested version of the AURAMS model was constructed for post-campaign simulations and evaluation against the measurement data. The nested model runs at different resolutions, the highest of which is a 3 km horizontal resolution centered on the urban area. The high resolution model results show good agreement with observations, with side-by-side sampling through the real and model atmosphere. The comparison shows the same features for particle composition (Aerodyne AMS measurements compared to speciated PM1), for airborne gases (continuous NO, NO2, O-3) and ground-based measurements of gases, particle composition and particle layering structure. The simulations reveal that air-quality in the Edmonton area is complex, largely due to multiple local sources, with occasional long-range-transport events.