Volatile organic compounds in the atmosphere of forests

The procedure of sampling and gas chromatographic-mass spectrometric analysis of air containing volatile emissions from living plants has been elaborated. The qualitative composition of volatile organic compounds (VOC) produced by 22 species of plants which are characteristic for Northern hemisphere forests has been studied. The emission rate of isoprene and terpenes for some of them has been determined. Terpene concentrations in coniferous forests of different regions of the U.S.S.R. have been also determined. The list of compounds identified includes more than 70 substances of different classes. Total terpene concentrations in the coniferous forests air usually vary from 3.5 to 35 μg⁻³. Strong influence of meteorological conditions on the emission rate and terpene concentrations in the air under the forest canopy has been noted.     

Ambient levels of volatile organic compounds in the atmosphere of Greater Cairo

Ambient volatile organic compounds (VOCs) samples were collected at three locations, two in urban areas in Greater Cairo (Ramsis and Haram) and background one in rural area in Menofiya province (Kafr El-Akram), during the period of June, 2004–August, 2004. The highest concentrations of VOCs were found in Ramsis, whereas the lowest concentrations were detected in Kafr El-Akram, and the difference in mean concentrations were statistically significant (p<0.001). Among all of the measured VOCs species, the contribution of individual VOC to the total VOCs concentration were very similar in Ramsis and Haram locations, toluene was the most abundant compound followed by (m, p)-xylene. This similarity implies a similar emission sources of VOCs in both urban locations, vehicle exhausts are the dominant one. Greater Cairo has high levels of volatile aromatic hydrocarbons compared with many polluted cities in the world. The BTEX (benzene: toluene: ethylbenzene: xylenes) concentration ratios were (2.01:4.94:1:4.95), (2.03:4.91:1:4.87) and (2.31:2.98:1:2.59) in Ramsis, Haram and Kafr El-Akram, respectively. The average toluene/benzene (T/B), (m, p)-xylene/benzene ((m, p)-X/B) and o-xylene/benzene (o-X/B) concentration ratios were 2.45, 1.61and 0.85, respectively in Ramsis and 2.42, 1.61 and 0.78, respectively in Haram. The ratios in both urban locations were of the same magnitude and close to those obtained from automotive exhausts, indicating that the ambient BTEX originate mainly from motor vehicle emissions. However, the (T/B), ((m, p)-X/B) and (o-X/B) concentration ratios were 1.29, 0.71 and 0.41 in Kafr El-Akram, respectively. These ratios were lower than those found in Ramsis and Haram locations and in automotive exhaust, suggesting that the BTEX in Kafr El-Akram do not come from a local source and are exclusively results from the diffusion and dispersion of VOCs produced from the traffic density in the surrounding cities. Significant positive correlation coefficients (p<0.001) were found between the concentrations of BTEX compounds at the three sampling locations. The diurnal variation of VOCs concentrations in Ramsis location showed two daily peaks linked to traffic density.     

Particulate organic compounds emitted from motor vehicle exhaust and in the urban atmosphere

The emission rate of particle-phase petroleum biomarkers in vehicular exhaust compared to the concentrations of these biomarkers in ambient air is used to determine the particulate organic compound concentration due to primary particle emissions from motor vehicles in the southern California atmosphere. A material balance on the organic particulate matter emitted from motor vehicle traffic in a Los Angeles highway tunnel first is constructed to show the proportion which is solvent-extractable and which will elute from a GC column, the ratio of resolved to unresolved compound mass, the portion of the resolved material that can be identified as single organic compounds, and the contribution of different classes of organic compounds to the overall identified fraction. It is shown that the outdoor ambient concentrations of the petroleum biomarkers track primary emissions measured in the highway tunnel, confirming that direct emissions of these compounds from vehicles govern the observed ambient petroleum biomarker concentrations. Using organic chemical tracer techniques, the portion of fine organic particulate matter in the Los Angeles atmosphere which is attributable to direct particle emissions from vehicle exhaust is calculated to vary from 7.5 to 18.3% at different sites throughout the air basin during a summertime severe photochemical smog episode. A similar level of variation in the contribution of primary motor vehicle exhaust to fine particulate organic matter concentrations during different times of day is seen. While peak atmospheric concentrations of fine particulate organic carbon are observed during the 1200–1600 PDT afternoon sampling period, only 6.3% of that material is apportioned to the directly emitted particles from vehicle exhaust. During the morning traffic peak between 0600–1000 PDT, 19.1% of the fine particulate organic material is traced to primary emissions from motor vehicles.     

Carbonyl compounds and dissolved organic carbon in rainwater of an urban atmosphere

This study investigates the occurrence of carbonyl compounds in rainwater at the city of Thessaloniki, Northern Greece. The concentrations of carbonyl compounds (as sum of 14 compounds) ranged from 21.8 to 592 μg/L, mean concentration 119 μg/L. Formaldehyde, acetaldehyde, hexanal, glyoxal, and methylglyoxal were the dominant compounds. DOC concentrations in rainwater ranged from 0.46 to 21.3 mg/L. UV–Vis and fluorescence spectra characteristics showed variation among rain events. Carbonyl compounds were negatively correlated with temperature exhibited relatively higher concentrations in cold season. They also influenced by storm origin with higher concentrations under terrestrial air masses. Calm conditions enhance the concentrations of DOC. Wash out is an effective removal mechanism of DOC.     

Concentrations of volatile organic compounds in an industrial area of Korea

We measured and analyzed daily mean concentrations of volatile organic compounds (VOC) at Ulsan industrial and downtown sites from 3 to 8 June 1997. The industrial site is situated at the boundary of a petrochemical complex and the other is at downtown area in Ulsan. At each site, we collected ambient air samples in passivated stainless-steel containers by using constant flow samplers and analyzed them by a GC-FID. At Ulsan industrial site, the concentrations and their daily variations of total VOC were higher than those at the downtown site. The concentrations of oxygenated hydrocarbons were the highest among seven hydrocarbon groups at both sites. The fraction of C₂–C₅ light hydrocarbon concentrations to C₂–C₉ hydrocarbons at Ulsan industrial site was higher than that in other industrial areas. It suggests that fugitive emissions of light hydrocarbons in Ulsan industrial areas might be higher than those of other industrial areas. Under favorable wind conditions, the influence of industrial emissions of VOC on the downtown hydrocarbon levels was observed.     

Volatile organic compounds (VOCs) in urban atmosphere of Hong Kong

The assessment of volatile organic compounds (VOCs) has become a major issue of air quality network monitoring in Hong Kong. This study is aimed to identify, quantify and characterize volatile organic compounds (VOCs) in different urban areas in Hong Kong. The spatial distribution, temporal variation as well as correlations of VOCs at five roadside sampling sites were discussed. Twelve VOCs were routinely detected in urban areas (Mong Kok, Kwai Chung, Yuen Long and Causeway Bay). The concentrations of VOCs ranged from undetectable to 1396 microg/m3. Among all of the VOC species, toluene has the highest concentration. Benzene, toluene, ethylbenzene and xylenes (BTEX) were the major constituents (more than 60% in composition of total VOC detected), mainly contributed from mobile sources. Similar to other Asian cities, the VOC levels measured in urban areas in Hong Kong were affected both by automobile exhaust and industrial emissions. High toluene to benzene ratios (average T/B ratio = 5) was also found in Hong Kong as in other Asian cities. In general, VOC concentrations in the winter were higher than those measured in the summer (winter to summer ratio > 1). As toluene and benzene were the major pollutants from vehicle exhausts, there is a necessity to tighten automobile emission standards in Hong Kong.     

Concentrations and fluxes of tin in aerosols and rain

The concentration of tin in atmospheric aerosols has been measured at land and ship based sites in the northern and southern hemispheres. Tin concentrations in the northern hemisphere are up to three orders of magnitude greater than those in the southern hemisphere, indicating the importance of anthropogenic inputs to the atmospheric tin cycle. In aerosols sampled in Tallahassee, Florida, tin is correlated with soot carbon in air masses originating in the central U.S., but is not correlated with locally produced soot carbon. Rainwaters collected in Tallahassee, Florida have been analyzed for dissolved tin and major ions. Factor analysis of the results indicates a continental and pollution source for tin. The dissolved fraction of tin in rain represents only a minor component of the deposition flux of tin. Rates of deposition of atmospheric tin are consistent with estimated fluxes of tin to the atmosphere.     

Mixing ratios of volatile organic compounds (VOCs) in the atmosphere of Karachi,Pakistan

Mixing ratios of carbon monoxide (CO), methane (CH₄), non-methane hydrocarbons, halocarbons and alkyl nitrates (a total of 72 species) were determined for 78 whole air samples collected during the winter of 1998–1999 in Karachi, Pakistan. This is the first time that volatile organic compound (VOC) levels in Karachi have been extensively characterized. The overall air quality of the urban environment was determined using air samples collected at six locations throughout Karachi. Methane (6.3 ppmv) and ethane (93 ppbv) levels in Karachi were found to be much higher than in other cities that have been studied. The very high CH₄ levels highlight the importance of natural gas leakage in Karachi. The leakage of liquefied petroleum gas contributes to elevated propane and butane levels in Karachi, although the propane and butane burdens were lower than in other cities (e.g., Mexico City, Santiago). High levels of benzene (0.3–19 ppbv) also appear to be of concern in the Karachi urban area. Vehicular emissions were characterized using air samples collected along the busiest thoroughfare of the city (M.A. Jinnah Road). Emissions from vehicular exhaust were found to be the main source of many of the hydrocarbons reported here. Significant levels of isoprene (1.2 ppbv) were detected at the roadside, and vehicular exhaust is estimated to account for about 20% of the isoprene observed in Karachi. 1,2-Dichloroethane, a lead scavenger added to leaded fuel, was also emitted by cars. The photochemical production of ozone (O₃) was calculated for CO and the various VOCs using the Maximum Incremental Reactivity (MIR) scale. Based on the MIR scale, the leading contributors to O₃ production in Karachi are ethene, CO, propene, m-xylene and toluene.     

上海城郊大气挥发性有机物污染特征、活性组分及风险评估

为了解上海城郊大气中挥发性有机物(VOCs)的时空污染特征及其对人体潜在健康风险,选取上海某城郊10个点位进行连续6年(2012—2017年)的采样分析。结果表明,上海该城郊大气VOCs平均质量浓度为(243.80±151.52)μg/m3,其中烷烃、卤代烃、芳香烃、含氧VOCs和不饱和脂肪烃依次占VOCs总浓度的45.72%、20.04%、18.84%、11.19%、4.21%。上海郊区不同功能区VOCs总浓度年际变化趋势较为一致,总体呈下降趋势;在空间上,化工区主干道路附近的两采样点VOCs质量浓度最高,分别为307.81、340.97μg/m~3。O3生成潜势和等效丙烯浓度计算结果显示,芳香烃为上海城郊大气中最主要的活性物种,且关键活性组分为甲苯、间/对-二甲苯和异丁烷等。上海城郊大气中27种风险VOCs的总致癌风险值为3.02×10~(-4),高于可接受限值(1.00×10~(-4)),长期暴露可能有致癌风险。     

A tool for estimating the contribution of water-soluble organic compounds to the particle mass and condensational growth in the atmosphere

In this theoretical investigation, we elucidated several factors governing the ability of organic, water-soluble vapours to participate into either the secondary organic aerosol formation or particle condensational growth in the atmosphere. The corresponding requirements for physico-chemical properties of the vapour were estimated. These estimates were also compared with the properties of several difunctional carboxylic acids identified in the atmosphere. Our analysis indicates that while many of the considered compounds are expected to contribute to the total particle mass in the atmosphere, their role in particle condensational growth process remains uncertain. This uncertainty emerges from the fact that the saturation ratio of an organic vapour does not alone determine its ability to act as a “nonvolatile” compound. Instead, the hygroscopic and chemical properties of the vapour, as well as the particle pH and size, have also to be taken into account.     

A comparative evaluation of passive and active samplers for measurements of gaseous semi-volatile organic compounds in the tropical atmosphere

The polyurethane foam (PUF) disk-based passive air samplers (PAS), mounted inside two aluminium bowls to buffer the air flow to the disk and to shield it from precipitation and sunlight, were used for the collection of atmospheric SVOCs in Singapore during April 2008–June 2008. Data obtained from PAS measurements are compared to those from active high-volume air sampling (AAS). Single factor ANOVA tests show that there were no significant differences in chemical distribution profiles between actively and passively collected samples (PAHs, F = 3.38 × 10^?8 < F_critical = 4.17 with p > 0.05; OCPs, F = 2.71 × 10^?8 < F_critical = 4.75 with p > 0.05). The average air-side mass transfer coefficient (k_A) for PAS, determined from the loss of depuration compounds such as 13C₆ – HCB (1000 ng), 13C₁₂ – 4,4′ DDT (1000 ng) and 13C₁₂ – PCB 101 (1000 ng)spiked on the disks prior to deployment, was 0.12 ± 0.04 m s^?1. These values are comparable to those reported previously in the literature. The average sampling rate was 3.78 ± 1.83 m³ d^?1 for the 365 cm² PUF disk. Throughout the entire sampling period (～68 d), most of the PAHs and all OCPs exhibited a linear uptake trend on PAS, while naphthalene, acenaphthylene, acenaphthene and fluorene reached the curvilinear phase after the first ～30 d exposure. Theoretically estimated times to equilibrium (t_eq) ranged from around one month for Acy to hundreds of years for DB(ah)A. Sampling rates, based on the time integrated active sampling-derived concentrations and masses collected by PUF disks during the linear uptake phase, were determined for all target compounds with the average values of 2.50 m³ d^?1 and 3.43 m³ d^?1 for PAHs and OCPs, respectively. More variations were observed as compared to those from the depuration study. These variation were most likely due to the difference of physicochemical properties of individual species. Lastly, multiple linear regression models were developed to estimate the log-transformed gaseous concentration of an individual compound in air based on the mass collection rate of the gaseous SVOCs measured using the PAS and the molecular weight (MW) of the particular compound for both PAHs and OCPs, respectively.     

Homogeneous oxidation of sulphur compounds in the atmosphere

Work carried out under the European COST 61a Project on the homogeneous oxidation of sulphur compounds in the atmosphere is briefly reviewed. Mechanisms for sulphur dioxide can be divided into three classes;

• 1.(a) oxidation by free radicals generated photochemically,
• 2.(b) oxidation by intermediates produced in thermal reactions, and
• 3.(c) direct photo-oxidation.

Only (a) makes a substantial contribution to SO₂ oxidation with calculated maximum rates of between 2 and 6% h⁻¹ in sunlight irradiated urban air during summer months and 1–2% h⁻¹ in unpolluted air. Most of the oxidation is brought about by the attack of the OH radical on SO₂ but the contribution of RO₂ radical attack is not well determined due to uncertainties in RO₂ rate constants. H₂S, CH₃SH and (CH₃)₂S react with OH radicals giving atmospheric life-times about 1 day.     

Concentrations and sources of carbonaceous aerosol in the atmosphere of Summit,Greenland

High-volume PM_2.5 samples were collected at Summit, Greenland for approximately six months from late May through December of 2006. Filters were composited and analyzed for source tracer compounds. The individual organic compounds measured at Summit are orders of magnitude smaller than concentrations measured at other sites, including locations representative of remote oceanic, and remote and urban continental aerosol. The measured tracers were used to quantify the contribution of biomass burning (0.6–0.9 ng C m^?3), vegetative detritus (0.3–0.9 ng C m^?3), and fossil fuel combustion (0.1–0.8 ng C m^?3) sources, 4% of OC total, to atmospheric organic carbon concentrations at the remote location of Summit, Greenland. The unapportioned organic carbon (96%) during the early summer period correlates well with the fraction of water soluble organic carbon, indicating secondary organic aerosol as a large source of organic carbon, supported by the active photochemistry occurring at Summit. To the author's knowledge, this paper represents the first source apportionment results for the polar free troposphere.     

Seasonal distribution of polar organic compounds in the urban atmosphere of two large cities from the North and South of Europe

Polar organic species, including n-alkanols, sterols, anhydrosugars, n-alkanoic acids, n-alkenoic acids and dicarboxylic acids were quantified to typify the composition of fine (PM_2.5) and coarse (PM_10–2.5) aerosols collected simultaneously at roadside and background sites in Oporto (Portugal) and Copenhagen (Denmark) during separate month-long intensive summer and winter campaigns. As a general trend, both cities exhibit roadside average concentrations higher than their correspondent urban background levels. The polar organics are more abundant in the fine fraction, exhibiting a seasonal pattern with high winter concentrations and low summer loads. Aerosols from both cities showed typical distributions of n-alkanols and n-alkanoic acids in the ranges C₁₂–C₂₈ and C₈–C₂₈, respectively. The <C₂₀ homologues, usually attributed to kitchen emissions, vehicular exhausts and microbial origins, dominated the fatty acid fraction. Linear alcohols were mainly represented by higher molecular weight homologues from vegetation waxes. Molecular tracer species for wood smoke (e.g. levoglucosan, mannosan and resinic acids) were found to contribute significantly to the urban aerosol, especially in winter. Ratios between these tracers indicated different biofuel contributions to the atmospheric particles of the two cities. Secondary constituents from both biogenic (e.g. pinonic acid) and anthropogenic precursors (e.g. phthalic and benzoic acids) were detected in both cities and seasons.     

Verification of diffusive and pumped samplers for volatile organic compounds using a controlled atmosphere test facility

There is a requirement to verify the performance of sorbent-based passive or active samplers and to extend their use, where possible, to monitor volatile organic compounds (VOCs) that are known to be photochemical ozone pre-cursors or are relevant to the activities of the petrochemical industry. We report measurements of the 14-day diffusive uptake rates for the VOCs: i-butane (2-methyl propane), n-butane, i-pentane (2-methyl butane), n-pentane, n-hexane, benzene, toluene, and m-xylene (at environmental level concentrations) for industry standard axial samplers (Perkin–Elmer-type samplers) containing the sorbents Carbopack-X, -Z, -B or Tenax-TA. We also present data on back-diffusion, blank levels, and storage for the above sorbents, and describe the simultaneous use of the sorbent Carbopack-X for pumped sampling of certain VOCs. The results were obtained by dosing samplers in a controlled atmosphere test facility (CATFAC) operating under well-defined conditions of concentration, nominal temperature of 20 °C, wind speed of 0.5 m s^?1, and relative humidities of 0% and 80%. Field measurements were also obtained to provide supplementary data to support the laboratory study. Results are compared to existing published data, where these are available.     

Butyltins in water, biofilm, animals and sediments of the west coast of India

Biofilm, fish, oyster, mussel, clam, surface seawater, suspended particulate matter (SPM), and sediment samples were collected from marine and/or estuarine waters of the west coast of India. These samples were analysed for butyltin derivatives such as dibutyltin (DBT) and tributyltin (TBT). The concentrations DBT plus TBT varied between 2.4 and 8.3, 163 and 363 ng/l, 5 and 2853 ng/g dry wt in the SPM, seawater and sediment samples, respectively, of the Marmugao harbour. The values of DBT plus TBT ranged between 0.60 and 29, 123 and 242 ng/l and 1.4 and 65 ng/g dry wt in SPM, water and sediment samples, respectively, collected from the Mandovi estuary. In the Dona Paula Bay the DBT plus TBT varied from 10 to 89 ng/l in surface seawater, and TBT from 10 to 513 ng/g in biofilm samples. For the coastal sediment samples the concentration of DBT plus TBT ranged between 36 and 133 ng/g dry wt of sediment. For the animal samples the DBT plus TBT ranged between 58 and 825 ng/g dry wt of the tissue. Mussel tissues contained the highest amount of DBT plus TBT (825 ng/g dry wt tissue), whereas highest TBT concentration was recorded in the oyster (732 ng/g dry wt). TBT was generally the most abundant butyltin compound in most of the samples suggesting fresh inputs and/or less degradation of TBT. A wide range of the observed butyltin concentrations suggests the presence of localized areas of contamination. Leaching of tributyltin-containing antifouling paints from the ocean going ships, fishing and recreational boats, barges, and the inputs of TBT from the Goa shipyard and dry dock facility situated in the harbour are the probable sources of the DBT and TBT in the samples of the west coast of India. Higher levels of TBT were observed in biofilm relative to that in the surrounding seawater. When fed on TBT contaminated biofilm of the diatom Navicula subinflata, butyltin concentrations in the clam Paphia malabarica increased over the period of feeding suggesting the importance of biofilm in the transfer of butyltins to higher group of organisms.     

Secondary organic aerosol importance in the future atmosphere

In order to investigate the secondary organic aerosol (SOA) response to changes in biogenic volatile organic compounds (VOC) emissions in the future atmosphere and how important will SOA be relative to the major anthropogenic aerosol component (sulfate), the global three-dimensional chemistry/transport model TM3 has been used. Emission estimates of biogenic VOC (BVOC) and anthropogenic gases and particles from the literature for the year 2100 have been adopted.According to our present-day model simulations, isoprene oxidation produces 4.6 Tg SOA yr⁻¹, that is less than half of the 12.2 Tg SOA yr⁻¹ formed by the oxidation of other BVOC. In the future, nitrate radicals and ozone become more important than nowadays, but remain minor oxidants for both isoprene and aromatics. SOA produced by isoprene is estimated to almost triple, whereas the production from other BVOC more than triples. The calculated future SOA burden change, from 0.8 Tg at present to 2.0 Tg in the future, is driven by changes in emissions, oxidant levels and pre-existing particles. The non-linearity in SOA formation and the involved chemical and physical feedbacks prohibit the quantitative attribution of the computed changes to the above-mentioned individual factors. In 2100, SOA burden is calculated to exceed that of sulfate, indicating that SOA might become more important than nowadays. These results critically depend on the biogenic emissions and thus are subject to the high uncertainty associated with these emissions estimated due to the insufficient knowledge on plant response to carbon dioxide changes. Nevertheless, they clearly indicate that the change in oxidants and primary aerosol caused by human activities can contribute as much as the change in BVOC emissions to the increase of the biogenic SOA production in the future atmosphere.     

Local fisheries management at the Swedish coast: biological and social preconditions

Most of the Swedish coastal fisheries are not sustainable from either a social, economic or ecological point of view. We propose the introduction of local fisheries management (LFM) as a tool for restructuring the present large-scale management system in order to achieve sustainability. To implement LFM two questions need to be answered: How to distribute the resource fish among different resource user groups? How to restructure present fisheries management to meet the criteria of sustainability? Starting from these questions we describe possible forms of LFM for Swedish coastal fishery supported by recent research. The biological and social preconditions for restructuring fisheries management are derived from an analysis of the ecological and managerial situation in Swedish fishery. Three types of LFM--owner based, user based, and community based management--are analyzed with regard to the tasks to be carried outin LFM, the roles of management groups, and the definition and optimal size of management areas.     

Input-export fluxes of heavy metals in the Cochin estuary,southwest coast of India

Cochin estuary (CE) is one of the largest tropical estuaries along the southwest coast of India, sustaining rich bio-resources. Several studies enlighten the environmental changes in the CE caused by anthropogenic activities. In the present study, an attempt has been made to quantify the heavy metal (dissolved and particulate) fluxes brought by the six rivers into the CE with their exchange into the coastal ocean through the major inlet at Cochin during a steady flow period (October–November 2015). The water flux across the inlet was quantified using an acoustic doppler current profiler. The measured daily input of dissolved metals from the rivers was 2.43?×?10³ kg Fe, 334 kg Zn, 259 kg Ni, and 83 kg Cr, while that of particulate metals were 85.30?×?10³ kg Fe, 8. 6?×?10³ kg Mn, 236.9 kg Cr, and 111.9 kg Zn. The net export of metals through the Cochin inlet (per tidal cycle) was 3.3?×?10³ kg Fe, 515 kg Cr, 150 kg Zn, and 5 kg Ni in dissolved form and 3.32?×?10⁵ kg Fe, 1747 kg Mn, 1636 kg Cr, 1397 kg Zn, and 586 kg Ni in particulate form. The high concentrations of metals during ebb tides are clear indications of their contribution from the industrial conglomerates (industrial units of metallurgy, catalyst, fertilizer, and pesticides) located in the Periyar River. The significance of this study is that the export fluxes may increase further during the summer monsoon (June to September), which may impact the abundant fishery emanating in the coastal environment during the period due to intense upwelling.

     

The distribution of particle-phase organic compounds in the atmosphere and their use for source apportionment during the Southern California Children''s Health Study

Atmospheric particulate matter (PM) samples from 12 sites in southern California, collected as part of the Southern California Children's Health Study (SCCHS), were analyzed using gas chromatography/mass spectrometry (GC/MS) techniques. Ninety-four organic compounds were quantified in these samples, including n-alkanes, fatty acids, polycyclic aromatic hydrocarbons (PAH), hopanes, steranes, aromatic diacids, aliphatic diacids, resin acids, methoxyphenols, and levoglucosan. Annual average concentrations of all detected compounds, as well as average concentrations for three seasonal periods, were determined at all 12 sites for the calendar year of 1995. These measurements provide important information about the seasonal and spatial distribution of particle-phase organic compounds in southern California. Also, co-located samples from one site were analyzed to assess precision of measurement. Excellent agreement was observed between annual average concentrations for the broad range of organic compounds measured in this study. Measured concentrations from the 12 sampling sites were used in a previously developed molecular-marker source apportionment model to quantify the primary source contributions to the PM10 organic carbon and mass concentrations at these 12 sites. Source contributions to atmospheric PM from six important air pollution sources were quantified: gasoline-powered motor vehicle exhaust, diesel vehicle exhaust, wood smoke, vegetative detritus, tire wear, and natural gas combustion. Important trends in the seasonal and spatial patterns of the impact of these six sources were observed. In addition, contributions from meat smoke were detected in selected samples.