A nonderivatization analytical method has been developed to analyze C-6-C-20 fatty acids and cis-pinonic acid on a GC/FID and a GC/MSD using a polar DB-FFAP capillary column. On the GC/FID, the response was highly linear over concentration ranges > 2 orders of magnitude (R-2 = 1.00). Using a mixed solvent of dichloromethane (DCM): methanol (3:1, v/v) and an extraction temperature of 40 degrees C, the method recoveries of the acids from spiked filters were 81-115% based on deuterated surrogates, and the relative standard deviations were < 12%. The recoveries were mainly controlled by the extraction temperature. At 40 degrees C the acids in sample extracts were stable for at least 12 months, while at 80 degrees C, unintended esterization of the acids by methanol was found that reduces their stability in the sample extracts. The analysis of the acids in PM2.5 samples from NIST using this nonderivatization method showed that the efficiency and accuracy were comparable to the derivatization method. Compared with existing derivatization methods,the method is accurate and sensitive, yet simple to use. This method was applied to PM2.5 ambient aerosols collected from a forest site and at a traffic tunnel outlet in the greater Vancouver area in Canada. Total fatty acids (sum of C-6-C-20) in the aerosols were measured as 20.2-138.7 ng/m(3) at the forest site and 100.2-264.6 ng/m(3) at the tunnel site. The cis-pinonic acid concentrations were 1.6-44.2 ng/m(3) in the forest and from below detection to 6.5 ng/m(3) at the tunnel outlet.

From 13 August-1 September 2001, a number of gaseous chemical compounds were measured at three sites in the Lower Fraser Valley, British Columbia: (1) Slocan-in the city of Vancouver; (2) Langley-in a rural, agricultural area about 35 km southeast of Vancouver; and (3) Sumas-about 65 km inland on a forested mountain (300m asl). Although the Langley and Sumas sites were located away from major emission sources, CO, NOx and NOy mixing ratios indicate that these sites were often impacted by anthropogenic emissions. At Langley and Slocan, NO and CO mixing ratios were highest between 0400-0700 PDT (UT=PDT-8h) due to the buildup of fresh vehicular emissions under a nocturnal inversion. At the elevated Sumas site, during the growth of the boundary layer, upward mixing of fresh emissions was observed, delayed by 3 h compared to the other two sites. NOx was the largest component of NOy at Langley and Sumas, averaging 75-80%. At Langley, the HNO3 fraction of NOy during the afternoon ranged from 15% to 28%, compared to <10% at the other two sites. PAN was significantly lower than HNO3 at <5% of NOy at all three sites. The sum of all individual nitrogen oxide species, SigmaNO(yi) accounted for 85% and 93% of NOy on average at Langley and Sumas, respectively. The chemical age was estimated at the three sites using the ratio (HONO+HNO3+PAN)/NOy. The daytime (1400-1800 PDT) ratios at Langley (0.19-0.40) were higher than those at either Slocan (0.04-0.12) or Sumas (0.09-0.19), mainly driven by higher HNO3 contributions to NOy. The higher ratios at Langley suggest that the extent of processing in air masses at the site during the daytime was greater than at Slocan or Sumas. At Sumas, the elevated nighttime ratios (0.05-0.29) were attributed to transport of more aged air masses to the site and the contribution of HNO3 from N2O5 hydrolysis. O-3 was only weakly correlated with the oxidation products of NOx at Langley (m = 2.5 +/- 9.1) and Sumas (m = 7.3 +/- 8.2). Meteorological conditions (lower radiation levels, cooler temperatures) were not favourable for photochemical pollutant processing. The dominant NOx fraction of NOy (see Section 3.2.1) clearly shows that most of the oxidized nitrogen remained in the form of NOx with very limited chemical processing and relatively low O-3 levels. Crown Copyright (C) 2004 Published by Elsevier Ltd. All rights reserved.

Two Aerodyne Aerosol Mass Spectrometers (AMS) were deployed at three sites representing urban, semi-rural and rural areas during the Pacific 2001 experiment in the Lower Fraser Valley (LFV), British Columbia, Canada in August 2001. The AMS provides on-line quantitative measurements of the size and chemical composition of the non-refractory fraction of submicron aerosol particles. A significant accumulation mode with a peak around 400-500 nm was observed at all sites that was principally composed of sulphate, organics, ammonium and some nitrate. Another significant mode with a peak below 200 nm was also observed at the urban site and when urban plumes affected the other sites. This paper focuses on the variability of the organic particulate composition and size distribution as a function of location and photochemical activity with a particular emphasis on the urban and rural areas. The small organic mode at the urban site was well correlated with gas phase CO, 1,3-butadiene, benzene and toluene with Pearson's r values of 0.76, 0.71, 0.79 and 0.69, respectively, suggesting that combustion-related emissions are likely to be the main source of the small organic mode at this site. The mass spectra of the urban organic particulate are similar to those of internal combustion engine lubricating oil, and of diesel exhaust aerosol particles, implying that they were composed of a mixture of n-alkanes, branched alkanes, cycloalkanes, and aromatics. In contrast, organic particulate at the rural site was dominated by shorter chain oxidized organic compounds. Correlations between the two organic modes and gas phase compounds at the rural site indicated that a significant part of the small mode originated from combustion sources, while the large accumulation organic mode appeared to be the result of photochemical processing. Processing of organic particulate during a relatively high O-3 episode at the rural site appeared to increase the modal diameter of the accumulation mode from about 400 to 600 nm and almost doubled its mass loading. (C) 2004 Elsevier Ltd. All rights reserved.

In order to characterize sources of fine carbonaceous aerosols, PM2.5 aerosols were sampled at 5 sites in forest, tunnel, urban, rural., and forest/urban areas in the Lower Fraser Valley (LFV) during the Pacific 2001 Air Quality Study. All sample filters were analyzed for cis-pinonic acid and n-fatty acids. cis-Pinonic acid varied from 0.6-46.5 ng m(-3) at the sites in the forest, rural and forest/urban mixing area, and was low, from < detection limit to 6.5 ng m(-3) at the tunnel and 0.3 to 20.4 ng m(-3) at the urban site. It showed consistent day-night differences at all locations, and was linearly correlated with alpha-pinene in forest areas. At the elevated mixing forest/urban site, the day-night pattern showed evidence of nighttime source of the acid. Straight-chain n-fatty acids on the aerosols showed evidence of the light-duty automobile source at the tunnel, with the highest concentration of all sites and a carbon number distribution with low CPI values. In the forest, the acids were the second highest of all sites, and the CPI value for the acids was the highest of all sites, indicating direct forest emissions. At other locations the n-fatty acids showed impacts from these sources, judging from the carbon number distributions. At the urban sites, there was evidence of meat cooking emissions contribution to the n-fatty acids. It was found that unsaturated n-fatty acids may be used as an indicator of the apparent ``age'' of the acids in aerosols, and that a photochemical half-life of 5 h was derived based on the comparison of the day and nighttime C-18:1/C-18:0 ratios at the sites. (C) 2004 Elsevier Ltd. All rights reserved.

Measurements of a number of aerosol properties and trace gases were conducted at Golden Ears Provincial Park (GE park), near the town of Maple Ridge, B.C., Canada from 6th to 11th of August 2001, just prior to the beginning of the main Pacific 2001 study. The measurements were intended to help with the characterization of the particulate matter (PM) in the forest that borders the northern side of the Lower Fraser Valley (LFV). The concentrations of inorganic ions in the particles decreased after 8th August, while the organic mass concentrations in the particles increased after 8th August. Throughout the study, organic carbon (OC) was the single highest component of the aerosol, and after 8th August, OC comprised about 90% of the particle composition. During the daytime, there was a clear anthropogenic influence from upslope flow driven by the sea breeze. The mixing ratio of monoterpenes increased overnight, when the winds were from the forests to the north but the cis-pinonic acid increased during the day, along with the anthropogenic tracers, suggesting that the oxidation of monoterpenes occurred with the help of anthropogenic oxidants. The particle volume data showed increases often corresponding with decreases in monoterpenes. A steady increase in particle volumes resulted from condensation of OC on the particles, and despite an increase in water soluble organic carbon (WSOC) the effectiveness of the OC at absorbing water for relative humidity (RH) values less than or equal to90% was low relative to sulphate. (C) 2004 Elsevier Ltd. All rights reserved.

High-resolution size-resolved mass concentration of organic and inorganic species present in/on sub-micron particles measured during the PACIFIC 2001 field study in the Lower Fraser Valley (LFV) are presented. The measurements of major particulate species (organics, sulfate, nitrate and ammonium) were made in situ and in real time at three different sites representing urban (Slocan Park), semi-rural (Sumas) and rural (Langley) areas, using two Aerodyne aerosol mass spectrometers (AMSs). The total non-refractory PM1.0 mass concentrations at the three sites were found to range from 0.12 to 24.50 mug m(-3), with an average concentration of 4.76 mug m(-3.) A large variability in aerosol composition was observed in the LFV, depending on meteorological conditions. Generally, during southwesterly wind conditions, inorganic species accounted for 50% of total mass loadings in the LFV, while during stagnant conditions organic species made up the majority of the particle mass. The organic aerosol species exhibit a bimodal size distribution, while the inorganic species are in most cases confined to the accumulation mode centered around 400 nm. Background sulfate levels of similar to 1 mug m(-3) were observed in the LFV during the entire campaign. Transport is found to be an important factor controlling the composition of sulfate in the LFV. Several photochemical events leading to the observation of substantial increases of sulfate in the LFV were also identified. Many of these events involve sulfate-dominated growth of small particles and appear to occur on a regional scale within the LFV. (C) 2004 Elsevier Ltd. All rights reserved.

The Pacific 2001 Air Quality Study was a major program on ambient particulate matter carried out in the Lower Fraser Valley. This paper provides an overview of the study and gives accounts of the measurements in each major components of the field measurement program, including ground sites specifically targeted on traffic emissions, urban mixing, urban to rural transition, biogenic emissions from forest, and a mixture of urban and forest, and an airborne measurement program to link the ground based components. A summary of major findings is given in the paper, along with a general background for the papers in this issue. (C) 2004 Elsevier Ltd. All rights reserved.

An analytical method has been developed to determine long-chain n -alkan-2-ones (C-10-C-33 ) in atmospheric particulate matter. This involves (1) solvent extraction with a Dionex Accelerated Solvent Extractor (ASE 200), followed by nitrogen blowdown; (2) a clean-up procedure using silica-gel chromatography to separate fractions of different polarities; and (3) gas chromatography with mass-selective detector (GC/MSD) identification and gas chromatography with flame ionization detector (GC/FID) quantitation. The recovery rates in the extraction/blowdown steps were quantified at different extraction and blowdown temperatures. The maximum recoveries for the selected ketones, obtained at 40degreesC for both extraction and blowdown, are 70-100% for the extraction step and 92-101% for the combined steps of blowdown and silica gel separation depending on the chain length of the ketones. The overall analytical instrumental detection limits for the ketones are <0.24 ng/muL in the GC/FID.

[1] Waliguan Observatory (WO) is a land-based Global AtmosphereWatch baseline station on the Tibetan Plateau. Size-resolved ionic aerosols (NH4(+), Na+, K+, Ca2+, Mg2+, SO24- , Cl-, NO3- CO32-, formate, acetate and oxalate), organic aerosols, black carbon and gaseous HNO3 and SO2 were measured during an intensive fall-winter field experiment. The observational data were analyzed with a focus on the partitioning of nitrate between the gas and particle phases. Nitrate was found to exist mainly in the particle phase with a typical particulate-to-total nitrate ratio, i.e., NO3-(p)/(NO3-(p) + HNO3(g)), of about 0.9. It was also found that the size distribution pattern of particulate nitrate at WO varied in different samples and the amount of particulate nitrate residing in the fine mode (D-p < 2.0 mu m) was typically larger than or comparable with that in the coarse mode. A gas-particle chemical equilibrium model was used to predict these particulate nitrate size distributions. The size distributions of particulate nitrate were reasonably reproduced with the model within the uncertainties caused by the detection limits. The chemical pathways for the formation of particulate nitrate at WO were analyzed with the size distributions of measured ionic aerosols. It was demonstrated that fine nitrate particles may have been produced by the reaction of gaseous nitric acid with gaseous ammonia, while coarse nitrate particles may have been generated via the condensation of nitric acid on the surface of mineral aerosols. The signature of biomass burning at WO was found to be associated with black carbon as well as the accumulation of potassium and oxalate in the fine particles.

Halogenated dicarboxylic acids, such as bromomalonic (Br-C-3), chlorosuccinic (Cl-C-4) and bromosuccinic (Br-C-4) acids, have been measured, for the first time, in the arctic aerosols during the polar sunrise experiment ALERT2000 ( February to May). They were detected in the light spring, but not in the dark winter. Concentration ranges of halogenated diacids in the spring were 0.11-0.68 ng m(-3) for Br-C-3 diacid, 0.04-0.10 ng m(-3) for Cl-C-4 diacid and 0.12-0.20 ng m(-3) for Br-C-4 diacid. Those of Br-C-3 diacid increased from late April to early May, whereas Cl-C-4 diacid decreased. In contrast, Br-C-4 diacid showed maximum concentrations in the middle of the experiment. A strong negative correlation (R = - 0.98) was obtained between Br-C-3 and Cl-C-4 diacids. Concentrations of methanesulfonic acid (MSA) also increased from late April to early May whereas those of Cl- ion decreased. A strong positive correlation was found between Cl-C-4 diacid and Cl- ion (R = 0.99) and between Br-C-3 diacid and MSA (R = 0.96). These results suggest that Br-C-3 diacid is primarily derived from marine biogenic source, whereas Cl-C-4 diacid is secondarily formed by heterogeneous reaction involving halogen chemistry on sea salt. Satellite images of sea ice concentrations and backward air mass trajectories suggest that the aerosols containing halogenated diacids were transported over the sampling sites from the Arctic Ocean covered with sea ice.

Saturated (C(2)-C(11)) and unsaturated (C(4)-C(5), C(8)) dicarboxylic acids were measured in Arctic aerosol and surface snowpack samples collected during dark winter (February) and light spring (April-May) using a gas chromatography and gas chromatography/mass spectrometry. Their molecular distributions were characterized by a predominance of oxalic acid (C(2)), except for few spring snowpack samples that showed the predominance of succinic acid (C(4)). Concentrations of short-chain saturated diacids (C(3)-C(5)) and 4-ketopimelic acid in the aerosol samples increased by a factor of similar to5 from winter to spring. In contrast, those of saturated C(6)-C(11) diacids and unsaturated (maleic, methylmaleic and phthalic) acids decreased by a factor of similar to4 from winter to spring aerosol samples. Snowpack samples also showed a similar trend. These results of the aerosol samples suggested that, the diacids are largely produced in spring by photochemical oxidation of hydrocarbons and other precursors that are transported long distances from the mid- and low-latitudes to the Arctic, but the production of oxalic acid is in part counteracted by photo-induced degradation possibly associated with bromine chemistry. (C) 2002 Elsevier Science Ltd. All rights reserved.

A multiphase chemical box model of Arctic halogen chemistry has been developed using a PC-based modeling program developed by Environment Canada called the Chemical Reactions Modeling System(CREAMS). The multiphase model contains 125 gas phase reactions, 19 photolysis reactions, and 16 aqueous reactions occurring in suspended aerosol particles and the quasi-liquid component of snow. The model simulates mass transfer of species between the gas phase and particles, and between the gas phase and the snowpack. Model simulations were conducted for the Arctic for the period April 16 to April 24 at 245 K within a 400 m boundary layer. The complete model simulates halogen-catalyzed ozone depletion within 5 days from the start of the model run, via known gas and heterogeneous phase activation mechanisms. A critically important model reaction is BrO + HCHO –> HOBr + CHO, which has a substantial impact on gas phase HOBr, and subsequent condensed phase chemistry. When coupled with a necessary snowpack efflux of aldehydes, required to maintain the aldehyde concentrations at observed levels, the new BrO chemistry has a significant impact on the concentrations of gas phase bromine species, particle bromide, and chlorine atoms, through chemistry occurring in the snowpack. We also find that O-3 depletion cannot be simulated without the presence of heterogeneous halogen chemistry occurring in the snowpack and that the rate of O-3 depletion is limited by the mass transfer rate of HOBr to the snowpack.

Measurements at the GAW station in western China reveal the levels and size distributions of chemical components in aerosols. The results indicate similarly high levels of three components, water-soluble organic carbon (WSOC), Ca2++CO3= and NH4++SO4=. Both WSOC and SO4= show a dominant accumulation mode, with a geometric mean mode diameter D-g of 0.41 and 0.34 mu m and geometric standard deviation sigma(sg) of 0.31 and 0.33, respectively. This mode makes up >70% of the total mass of both species. In comparison, Ca2+ and CO3= show a prominent coarse mode with D-g of 2.98 and 1.76 mu m and sigma(sg) of 0.29 and 0.22, respectively, that accounts for >60% of the mass. Based on these characteristics, estimates of the volume scatter coefficient beta, direct back scatter coefficient beta(pi) and mass scattering efficiency phi for each component were made, assuming external mixing and optical and growth characteristics of corresponding pure chemical compounds. The results show that NH4++SO4= has the largest beta, beta(pi) and phi (median 1760x10(-8) m(-1), 79x10(-8) m(-1) sr(-1), and 6.9 m(2) g(-1), respectively). It is followed by WSOC with 1470x10(-8) m(-1), 30x10(-8) m(-1) sr(-1), and 5.3 m(2) g(-1) for beta, beta(pi), and phi, respectively. Ca2++CO3= has only about 10% of the beta and phi values but 20% of the beta(pi) of NH4++SO4= respectively. For both NH4++SO4= and WSOC, the mass scattering efficiency phi is inversely related to their D-g between the size range of 0.2-0.45 mu m.

From July 1993 to September 1994, seasonal variations in the sources of SO42- aerosols in the Arctic lower atmosphere at Alert, Canada, (82 degrees 30' N, 62 degrees 20'W) were investigated using the sulphur isotope abundance of as little as 10 mu g of sulphur analyzed by combustion-flow isotope-ratio mass spectrometry. In conjunction with air mass trajectories and in parallel with measurements of aerosol composition, the sulphur isotope composition was used to discern sources of aerosol SO42-. Total SO42- is composed of seasalt SO42-, marine biogenic, and nonmarine SO42-. From June through September the fraction of biogenic SO42- in the non-sea-salt (nss) component ranged from 0.09 to 0.40 with an average of 0.31 +/- 0.11. Summertime nonmarine SO42- is likely anthropogenic in origin since it is isotopically indistinguishable from SO42- in the polluted winter/spring period of arctic haze (delta(34)S = +5 parts per thousand). In summer there was no significant difference in isotope composition of aerosol sulphate between air which recently traversed Eurasia and the Arctic Ocean and air arriving from North America. In contrast to summer and late winter/spring, delta(34)S values for nonmarine SO42- in fall and early winter were often less than +5 parts per thousand. These isotopically light samples were divisible into two groups: (1) those associated with air mass trajectories potentially affected by North American soils and/or smelters and (2) three weekly samples between October and December which could be attributed to fractionated sea-salt aerosol formed on refrozen Arctic Ocean leads. For the latter the ratio of SO42-/Na was estimated to be a factor of 3.6 lower than in bulk seawater. From November to May, nonmarine aerosol SO42- was apportioned into 10 aerosol components using positive matrix factor analysis of 18 aerosol ions and trace elements [Sirois ann Barrie, this issue]. In turn, a multiple linear regression of delta(34)S values against the scores of the components was used to predict the isotope composition of six components. It was concluded that the main mass of anthropogenic SO42- had a delta(34)S value near +5 parts per thousand and that biogenic SO42- had a delta(34)S Of +16 +/- 3.9 parts per thousand. Reasonable agreement between model results and sulphur isotope measurements at Alert show that SO42- apportionment using positive matrix factor analysis is a reasonable approach which gives realistic results.

Ground level measurements of aerosol physical and chemical properties were conducted at Ny Alesund on Spitsbergen from late March to mid-May 1996 as part of the European Arctic Tropospheric Ozone Chemistry study (ARCTOC'96) using laser-scattering aerosol-spectrometer probes and a denuder-filterpack system. When the air comes from Eurasia, the number, area, and volume distributions of aerosols at Ny Alesund are similar to those observed in the high Arctic at Alert, Canada, while when air comes off open water areas of the North Atlantic or Greenland, they are most different. The marine air has relatively more supermicrometer particles than the polluted arctic air. In Eurasian air the inorganic ionic component is dominated by H+ and SO4= and to a lesser extent NH4+. The average molar ratio of NH4+/H+ is 1/3. The average dry aerosol mass concentration and composition at Ny Alesund varied depending on origin of air. The period mean mass concentration was 4.1 mu g m(-3). It was lowest (2.2 mu g m-3) in air coming from the open North Atlantic and Greenland and was highest (6.2 mu g m(-3)) in air coming from the east. On average, aerosols in the North Atlantic and Greenland air were composed of 19% non-sea-salt SO4=, 22% sea salt, 25% ``other inorganic ions,'' and 34% of an uncharacterized residual fraction that is likely mostly carbonaceous compounds. In contrast, for the most polluted eastern air these fractions were 48% non-sea-salt SO4=, 7% sea salt, 8% other inorganic ions, and 37% residual. For the period the median diameters of the mean accumulation mode number, surface area, and volume distributions at ambient relative humidity (78-90%) were 0.23 mu m, 0.37 mu m, and 0.50 mu m effective scattering diameter (ESD), respectively. Number concentrations (for dry particle, diameters >0.065 mu m) ranged from 10 to 922 cm(-3) with an average of 270 cm(-3). Mixing ratios of particulate Br- compounds were observed to be anticorrelated with that of ozone, increasing markedly when the ozone mixing ratio was <10 nmol/mol. There was no obvious dependence of the ratio of gas to particle Br- on ozone mixing ratio. Observations suggested that during ozone depletion events the number concentration of particles increased in the 1.0 to 1.4 mu m ESD diameter range (ambient relative humidity).

The chemical composition of particles collected at Alert, Northwest Territories, Canada, show strong, persistent seasonal variations. In a previous study, a 2-way/3-way mixed factor model was performed on the weekly average concentrations of 24 aerosol components measured over the period from 1980 to 1991. The Multilinear Engine (ME), a new mathematical technique, was used to obtain the solution. The two modes of the 2-way model consist of the source composition profiles and mass contributions over the 11 yr, while for the three modes of the 3-way model, source profiles, mass contributions variations over the weeks within a year, and the year-to-year variation over the 11 yr within the measurement period. Five 2-way and two 3-way factors were found to provide a good fit to the data and were easily interpreted. In this investigation, potential source contribution function (PSCF) analysis was applied to the source contributions derived from the ME analysis by incorporating meteorological information in the form of 5-d air parcel back trajectories. The potential locations and/or the preferred pathways of these possible sources were then determined by the PSCF analysis. (C) 1999 Elsevier Science Ltd. All rights reserved.

Samples of airborne particulate matter were collected over a continuous sequence of 1 week intervals at Alert, Canada beginning in 1980 and analyzed for a number of chemical species, It was found that the measured weekly average concentrations display strong, persistent seasonal variations. In another recent study, the measured concentration of 24 constituents were arranged into both 2-way and 3-way data arrays and bilinear and trilinear models were used to fit the data using a new mathematical technique, positive matrix factorization. Five factors were found to explain the data for both 2-way and 3-way modeling with each factor representing a likely particle source. In the 2-way modeling, the yearly cyclical seasonal variations were not directly retrieved since the whole 11 yr of data was regarded as a single mode in the fitting. In the 3-way analysis, assuming the week-to-week patterns of the source contributions recur from year to year imposed fixed seasonality on the solutions. The resulting fit becomes worse if the year-to-year pattern of variation is not identical for any given source. These results suggested that a mixed model containing both 2-way and 3-way components might provide the best representation of the data. The methodology to calculate such a mixed model has just been developed. The multilinear engine is introduced in this study to estimate a mixed 2-way/3-way model for the Alert aerosol data. Five 2-way and two S-way factors have been found to provide the best fit and interpretation of the data. Each factor represented probable source with a distinctive compositional profile and seasonal variations. The five 2-way factors are (i) winter Arctic haze dominated by SO42- including metallic species with highest concentrations from December to April, (ii) soil represented by Si, Al, Ca, (iii) sea salt, (iv) sulfate with high acidity peaking in late March and April and (v) iodine representing most of the observed I with two maximal one around September and October and another around March and April. The two 3-way factors are (i) bromine characterized by a maximum in the spring around March and April; and (ii) biogenic sulfur which includes sulfate and methanesulfonate with maxims in May and August. The acidic sulfate, bromine, and iodine factors have a common maximum around March/April, just after polar sunrise, suggesting the influence of increased photochemistry at that time of year. The strength of the year-to-year biogenic sulfur factor showed a moderate correlation (r(2) = 0.5) with the yearly average Northern Hemisphere Temperature Anomaly suggesting a relationship of temperature with biogenic sulfur production. The results obtained are consistent with those obtained in the previous study and agree with the current understanding of the Arctic aerosol. (C) 1999 Elsevier Science Ltd. All rights reserved.

Week-long samples of airborne particulate matter were obtained at Alert, Northwest Territories, Canada, between 1980 and 1991. The concentrations of 24 particulate constituents have some strong, persistent seasonal variations that depend on the transport from their sources. In order to explore the nature of the cyclical variation of the different processes that give rise to the measured concentrations, the observations were arranged into both a two-way matrix and a three-way data array. For the latter the three modes consist of chemical constituents, weeks within a year, and years. The two-way bilinear model and a three-way trilinear model were used to fit the data and a new data analysis technique, positive matrix factorization (PMF), has been used to obtain the solutions. PMF utilizes the error estimates of the observations to provide an optimal pointwise scaling data array far weighting, which enables it to handle missing data, a common occurrence in environmental measurements. It can also apply nonnegative constraints to the factors. Five factors have been obtained that reproduce the data quite well for both two-way and three-way analyses. Each factor represents a probable source with a compositional profile and distinctive seasonal variations. Specifically, there are (i) an acid photochemical factor typified by Br-, H+, and SO42- and characterized by a concentration maximum around April, or shortly after polar sunrise; (ii) a soil factor representing by Si, Al, and Ca and having its main seasonal maximum in September and October; (iii) an anthropogenic factor dominated by SO42- together with metallic species like Pb, Zn, V, As, Sb, Se, In, etc., peaking from December to April; (iv) a sea salt factor consisting mainly of Cl, Na, and K with maximum concentrations during the period from October to April: and (v) a biogenic factor characterized by methane-sulfonate and having a primary maximum at May and a secondary maximum in August. The results obtained by both two-way and three-way PMF analyses are generally consistent with one another. However, there are differences because of additional constraints on the solution imposed by the three-way analysis. The results also help to confirm the hypotheses regarding the origins of the Arctic aerosol.

Aerosol and trace gas measurements were made at Kejimkujik National Park, Nova Scotia, Canada, during the summer of 1996. A case study from July 7-8 provides evidence of nucleation and condensation of products related to the oxidation of different biogenic emissions. Particles from 5 nm to 50 nm in diameter evolved during the afternoon and early evening associated with variations in isoprene. Late in the evening the alpha- and beta-pinene mixing ratios and the aerosol particle volume increased. Soon after, there was a sharp increase in RO2H/H2O2 that persisted until about 0100 LT. The initial increases in the pinenes and aerosols were strong and influenced by changes in winds. After 2200 LT, and into the early morning, the winds were relatively steady, and the alpha- and beta-pinene mixing ratios continually decreased. The decay of alpha-pinene is explained through reaction with O-3. However, the addition of OH radicals from the reaction of terpenes with O-3 is necessary to explain the observed rate of decay of beta-pinene. During the same time, the aerosol volume increased with the decrease in alpha- and beta-pinene. The volume increase was distributed 40:60 between particles in a mode centered at 80-90 nm and particles > 150 nm. The fine particle mass concentrations of the measured inorganic ions (sulfate, nitrate, chloride, ammonium, sodium, acid calcium) and organic ions (oxalate, formate, acetate, pyruvate, propionate) account for 25-30% of the total aerosol volume during the period (2.7 mu m(3) cm(-3)) indicating that the aerosol volume increase was due to unidentified species. Assuming that the increase in the aerosol was the result of products from the oxidation of alpha- and beta-pinene, an aerosol mass yield of 13% is estimated. The concentrations of cloud condensation nuclei active at 0.2% supersaturation were enhanced by the appearance of the 80-90 nm mode pointing to at least some of these forest-generated particles as being able to serve as nuclei for cloud droplets at common atmospheric supersaturations.