Emission and long-range transport of gaseous mercury from a large-scale Canadian boreal forest fire

Field observations made at Harvard Forest [Petersham, MA, U.S.A. (42 degrees 54' N, 72 degrees 18' W)] during early July 2002 show clear evidence of long-range transport of gaseous mercury (Hg) in a smoke plume from a series of boreal forest fires in northern Quebec. These measurements indicated significant and highly correlated increases in Hg and CO during the plume event. The Hg:CO emissions ratio determined from the data (8.61 x 10(-8) mol mol(-1)) was combined with previously published information on CO emissions and biomass burned to determine a mean area-based Hg emission flux density for boreal forest fires (1.5 g Hg ha(-1)), annual Hg emissions from Canadian forest fires (3.5 tonnes), and annual global Hg emissions from boreal forest fires (22.5 tonnes). Annual Hg emissions from boreal fires in Canada may equal 30% of annual Canadian anthropogenic emissions in an average fire year and could be as high as 100% during years of intense burning. The Hg:CO emissions ratio of this study was much lower than those reported for a temperate forest in Ontario and a pine/shrub vegetation in South Africa, suggesting that fire emission is dependent on biome/species and that any extrapolation from a single fire event to determine the global fire emission is speculative.     

Particulate-phase and gaseous elemental mercury emissions during biomass combustion: controlling factors and correlation with particulate matter emissions

Mercury emissions from wildfires are significant natural sources of atmospheric mercury, but little is known about what controls speciation of emissions important to mercury deposition processes. The goal of this study was to quantify gaseous elemental mercury (GEM) and particulate-phase mercury (PHg) emissions from biomass combustion to identify key factors controlling the speciation. Emissions were characterized in an exhaust stack 17 m above fires using a gaseous mercury analyzer and quartz-fiber filters. Fuels included fresh and air-dried leaves, needles, and branches with different fuel moistures (9-95% of dry weight) and combustion properties (e.g., from < 10 to 90% of fire durations characterized by flaming phases). Fuel moisture was the overall driving factor defining emissions, with GEM being the dominant fraction (> or = 95%) in low moisture fuels and substantial PHg contributions--up to 50% of total mercury emissions--in fresh fuels. High PHg emissions were observed during smoldering combustion whereas flaming-dominated fires showed insignificant PHg emissions. PHg mass emissions were correlated with particulate matter (PM; r2 = 0.67), organic carbon (OC; r2 = 0.63) and sulfur (S; r2 = 0.46) mass emissions, but not with elemental carbon (EC) nor with the total mercury emissions. These data suggest that the formation of PHg involves similar processes as the formation of particulate OC, for example condensation of volatile species onto preexisting smoke particles during cooling and dilution. Based on the observed relationship between PM and OC mass concentrations and published emission inventories, we estimate global PHg emissions by wildfires of 4-5 Mg yr(-1).     

Mercury emission estimates from fires: an initial inventory for the United States

Recent studies have shown that emissions of mercury (Hg), a hazardous air pollutant, from fires can be significant. However, to date, these emissions have not been well-quantified for the entire United States. Daily emissions of Hg from fires in the lower 48 states of the United States (LOWER48) and in Alaska were estimated for 2002-2006 using a simple fire emissions model. Emission factors of Hg from fires in different ecosystems were compiled from published plume studies and from soil-based assessments. Annual averaged emissions of Hg from fires in the LOWER48 and Alaska were 44 (20-65) metric tons yr(-1), equivalent to approximately 30% of the U.S. EPA 2002 National Emissions Inventory for Hg. Alaska had the highest averaged monthly emissions of all states; however, the emissions have a high temporal variability. Emissions from forests dominate the inventory, suggesting that Hg emissions from agricultural fires are not significant on an annual basis. The uncertainty in the Hg emission factors due to limited data leads to an uncertainty in the emission estimates on the order of +/-50%. Research is still needed to better constrain Hg emission factors from fires, particularly in the eastern U.S. and for ecosystems other than forests.     

Emission of oxygenated polycyclic aromatic hydrocarbons from indoor solid fuel combustion

Indoor solid fuel combustion is a dominant source of polycyclic aromatic hydrocarbons (PAHs) and oxygenated PAHs (OPAHs) and the latter are believed to be more toxic than the former. However, there is limited quantitative information on the emissions of OPAHs from solid fuel combustion. In this study, emission factors of OPAHs (EF(OPAH)) for nine commonly used crop residues and five coals burnt in typical residential stoves widely used in rural China were measured under simulated kitchen conditions. The total EF(OPAH) ranged from 2.8 ± 0.2 to 8.1 ± 2.2 mg/kg for tested crop residues and from 0.043 to 71 mg/kg for various coals and 9-fluorenone was the most abundant specie. The EF(OPAH) for indoor crop residue burning were 1-2 orders of magnitude higher than those from open burning, and they were affected by fuel properties and combustion conditions, like moisture and combustion efficiency. For both crop residues and coals, significantly positive correlations were found between EFs for the individual OPAHs and the parent PAHs. An oxygenation rate, R(o), was defined as the ratio of the EFs between the oxygenated and parent PAH species to describe the formation potential of OPAHs. For the studied OPAH/PAH pairs, mean R(o) values were 0.16-0.89 for crop residues and 0.03-0.25 for coals. R(o) for crop residues burned in the cooking stove were much higher than those for open burning and much lower than those in ambient air, indicating the influence of secondary formation of OPAH and loss of PAHs. In comparison with parent PAHs, OPAHs showed a higher tendency to be associated with particulate matter (PM), especially fine PM, and the dominate size ranges were 0.7-2.1 μm for crop residues and high caking coals and <0.7 μm for the tested low caking briquettes.     

Emission factors and importance of PCDD/Fs, PCBs, PCNs, PAHs and PM10 from the domestic burning of coal and wood in the U.K

This paper presents emission factors (EFs) derived for a range of persistent organic pollutants (POPs) when coal and wood were subject to controlled burning experiments, designed to simulate domestic burning for space heating. A wide range of POPs were emitted, with emissions from coal being higher than those from wood. Highest EFs were obtained for particulate matter, PM10, (approximately 10 g/kg fuel) and polycyclic aromatic hydrocarbons (approximately 100 mg/ kg fuel for sigmaPAHs). For chlorinated compounds, EFs were highest for polychlorinated biphenyls (PCBs), with polychlorinated naphthalenes (PCNs), dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs) being less abundant. EFs were on the order of 1000 ng/kg fuel for sigmaPCBs, 100s ng/ kg fuel for sigmaPCNs and 100 ng/kg fuel for sigmaPCDD/Fs. The study confirmed that mono- to trichlorinated dibenzofurans, Cl1,2,3DFs, were strong indicators of low temperature combustion processes, such as the domestic burning of coal and wood. It is concluded that numerous PCB and PCN congeners are routinely formed during the combustion of solid fuels. However, their combined emissions from the domestic burning of coal and wood would contribute only a few percent to annual U.K. emission estimates. Emissions of PAHs and PM10 were major contributors to U.K. national emission inventories. Major emissions were found from the domestic burning for Cl1,2,3DFs, while the contribution of PCDD/F-sigmaTEQ to total U.K. emissions was minor.     

Emissions of polychlorinated dibenzodioxins and dibenzofurans and polychlorinated biphenyls from uncontrolled burning of garden and domestic waste (backyard burning)

To assess emissions of dioxins (chlorinated dibenzodioxins and dibenzofurans) and PCB from uncontrolled domestic combustion of waste ("backyard burning"), test combustions in barrels and open fires were monitored. The waste fuels used were garden waste, paper, paper and plastic packaging, refuse-derived fuel (RDF), PVC, and electronic scrap. Combustions including PVC and electronic scrap emitted several orders of magnitude more dioxins than the other waste fuels. Emissions from the other fuels had considerable variations, but the levels were difficult to relate to waste composition. Emission factors of PCDD/F and PCB from the backyard burning ranged from 2.2 to 13 000 ng (WHO-TEQ)/kg. The levels found in ash usually were less than 5% of the total. For assessment of total emissions of dioxins and PCB from backyard burning of low and moderately contaminated wastes, an emission factor range of 4-72 ng (WHO-TEQ)/kg is suggested. These figures implythat combusting waste in the backyard could contribute substantially to total emissions, even if the amounts of fuel involved are equivalent to just a few tenths of a percent of the amounts combusted in municipal waste incinerators.     

PCDD/F,PCB, HxCBz,PAH, and PM emission factors for fireplace and woodstove combustion in the San Francisco Bay region

Emissions from residential fireplace and woodstove appliances burning fuels available from the San Francisco Bay area were sampled for polychlorinated dibenzodioxins and dibenzofurans (PCDDs/Fs), polychlorinated biphenyls (PCBs), hexachlorobenzene (HxCBz), particulate matter (PM), polycyclic aromatic hydrocarbons (PAHs), oxygenated PAHs, and the monosaccharide levoglucosan. Emission factors for these pollutants were determined, the first known characterization of this extent. Common California natural firewoods and manufactured artificial logs were tested under operating conditions intended to reflect domestic use patterns in the Bay area, which are primarily episodic burning for aesthetic reasons. Emission factors were determined by fuel type, fuel weight, mass emission rates, and energy output, highlighting differences between fuel and combustion facility type. Average PCDD/F emissions factors ranged from 0.25 to 1.4 ng toxic equivalency (TEQ)/kg of wood burned for natural wood fuels and 2.4 ng TEQ/kg for artificial logs. The natural wood emission factors are slightly lower than those which had been estimated for the U.S. inventory. Background-corrected PCBs emitted from woodstove/oak combustion (8370 ng/kg) are 3 orders of magnitude higher in mass than total PCDDs/Fs; however, their toxicity (0.014 ng TEQ/kg) is significantly lower. HxCBz emission factors varied from 13 to 990 ng/kg and were likely fuel- and appliance-specific. Relative PAH concentrations of particle-phase compounds and emission factors were consistent with others' findings. A total of 32 PAH compounds, ranging in concentration from 0.06 to 7 mg/kg, amounted to between 0.12 and 0.38% of the PM mass, depending on the wood and facility type. Preliminary analyses suggest relationships between wood combustion markers and PCDD/F levels.     

Anthropogenic atmospheric emissions of antimony and its spatial distribution characteristics in China

An integrated inventory of atmospheric antimony (Sb) emissions from anthropogenic activities in China is compiled for the years 2005-2009. Emissions are estimated for all major anthropogenic sources for the first time. We estimate that the national emissions of antimony are 818 metric tons (t) in 2009, with the largest contribution from coal combustion at 61.8% of the total, while 26.7% of Sb is emitted from nonferrous metals smelting. Emissions are heaviest in Guizhou province, mainly due to small-scale combustion of high-Sb coal without emission control devices, and in Hunan province, where extensive smelting occurs. Furthermore, Sb emissions from 2188 large point sources and area sources are distributed within latitude/longitude-based grids with a resolution of 30 min × 30 min where Sb emissions are largely concentrated in highly populated and industrialized southwestern China, the east central region, and coastal areas. The uncertainties in our bottom-up inventory are quantified as -11% to 40% by Monte Carlo simulation. We recommend continuous field testing of coal combustors and smelters in China to improve the accuracy of these estimates.     

Atmospheric emission of reactive nitrogen during biofuel ethanol production

This paper evaluates emissions to the atmosphere of biologically available nitrogen compounds in a region characterized by intensive sugar cane biofuel ethanol production. Large emissions of NH3 and NOx, as well as particulate nitrate and ammonium, occur at the harvest when the crop is burned, with the amount of nitrogen released equivalent to approximately 35% of annual fertilizer-N application. Nitrogen oxides concentrations show a positive association with fire frequency, indicating that biomass burning is a major emission source, with mean concentrations of NOx doubling in the dry season relative to the wetseason. During the dry season biomass burning is a source of NH3, with other sources (wastes, soil, biogenic) predominant during the wet season. Estimated NO2-N, NH3-N, NO3- -N and NH4+ -N emission fluxes from sugar cane burning in a planted area of ca. 2.2 x 10(6) ha are 11.0, 1.1, 0.2, and 1.2 Gg N yr(-1), respectively.     

Effect of fuels and domestic heating appliance types on emission factors of selected organic pollutants

This study reports on the first complex data set of emission factors (EFs) of selected pollutants from combustion of five fuel types (lignite, bituminous coal, spruce, beech, and maize) in six different domestic heating appliances of various combustion designs. The effect of fuel as well as the effect of boiler type was studied. In total, 46 combustion runs were performed, during which numerous EFs were measured, including the EFs of particulate matter (PM), carbon monoxide, polyaromatic hydrocarbons (PAH), hexachlorobenzene (HxCBz), polychlorinated dibenzo-p-dioxins and furans (PCDD/F), etc. The highest EFs of nonchlorinated pollutants were measured for old-type boilers with over-fire and under-fire designs and with manual stoking and natural draft. Emissions of the above-mentioned pollutants from modern-type boilers (automatic, downdraft) were 10 times lower or more. The decisive factor for emission rate of nonchlorinated pollutants was the type of appliance; the type of fuel plays only a minor role. Emissions of chlorinated pollutants were proportional mainly to the chlorine content in fuel, but the type of appliance also influenced the rate of emissions significantly. Surprisingly, higher EFs of PCDD/F from combustion of chlorinated bituminous coal were observed for modern-type boilers (downdraft, automatic) than for old-type ones. On the other hand, when bituminous coal was burned, higher emissions of HxCBz were found for old-type boilers than for modern-type ones.     

Particle size distribution and polycyclic aromatic hydrocarbons emissions from agricultural crop residue burning

Laboratory measurements were conducted to determine particle size distribution and polycyclic aromatic hydrocarbons (PAHs) emissions from the burning of rice, wheat, and corn straws, three major agricultural crop residues in China. Particle size distributions were determined by a wide-range particle spectrometer (WPS). PAHs in both the particulate and gaseous phases were simultaneously collected and analyzed by GC-MS. Particle number size distributions showed a prominent accumulation mode with peaks at 0.10, 0.15, and 0.15 μm for rice, wheat, and corn-burned aerosols, respectively. PAHs emission factors of rice, wheat, and corn straws were 5.26, 1.37, and 1.74 mg kg(-1), respectively. It was suggested that combustion with higher efficiency was characterized by smaller particle size and lower PAHs emission factors. The total PAHs emissions from the burning of three agricultural crop residues in China were estimated to be 1.09 Gg for the year 2004.     

Aerostat sampling of PCDD/PCDF emissions from the Gulf oil spill in situ burns

Emissions from the in situ burning of oil in the Gulf of Mexico after the catastrophic failure of the Deepwater Horizon drilling platform were sampled for polychlorinated dibenzodioxins and polychlorinated dibenzofurans (PCDD/PCDF). A battery-operated instrument package was lofted into the plumes of 27 surface oil fires over a period of four days via a tethered aerostat to determine and characterize emissions of PCDD/PCDF. A single composite sample resulted in an emission factor of 2.0 ng toxic equivalency (TEQ) per kg of carbon burned, or 1.7 ng TEQ per kg of oil burned, determined by a carbon balance method. Carbon was measured as CO(2) plus particulate matter, the latter of which has an emission factor of 0.088 kg/kg carbon burned. The average plume concentration approximately 200-300 m from the fire and about 75-200 m above sea level was <0.0002 ng TEQ/m(3).     

Emission factors, size distributions, and emission inventories of carbonaceous particulate matter from residential wood combustion in rural China

Published emission factors (EFs) often vary significantly, leading to high uncertainties in emission estimations. There are few reliable EFs from field measurements of residential wood combustion in China. In this study, 17 wood fuels and one bamboo were combusted in a typical residential stove in rural China to measure realistic EFs of particulate matter (PM), organic carbon (OC), and elemental carbon (EC), as well as to investigate the influence of fuel properties and combustion conditions on the EFs. Measured EFs of PM, OC, and EC (EF(PM), EF(OC), and EF(EC), respectively) were in the range of 0.38-6.4, 0.024-3.0, and 0.039-3.9 g/kg (dry basis), with means and standard derivation of 2.2 ± 1.2, 0.62 ± 0.64, and 0.83 ± 0.69 g/kg, respectively. Shrubby biomass combustion produced higher EFs than tree woods, and both species had lower EFs than those of indoor crop residue burning (p < 0.05). Significant correlations between EF(PM), EF(OC), and EF(EC) were expected. By using a nine-stage cascade impactor, it was shown that size distributions of PM emitted from tree biomass combustions were unimodal with peaks at a diameter less than 0.4 μm (PM(0.4)), much finer than the PM from indoor crop residue burning. Approximately 79.4% of the total PM from tree wood combustion was PM with a diameter less than 2.1 μm (PM(2.1)). PM size distributions for shrubby biomasses were slightly different from those for tree fuels. On the basis of the measured EFs, total emissions of PM, OC, and EC from residential wood combustion in rural China in 2007 were estimated at about 303, 75.7, and 92.0 Gg.     

Effect of 2,4-Dichlorophenoxyacetic Acid (2,4-D) on PCDD/F Emissions from Open Burning of Biomass

To understand the effect of leaf-surface pesticides on emissions of PCDD/F during biomass burns, nine combustion experiments simulating the open burning of biomass were conducted. Needles and branches of Pinus taeda (Loblolly pine) were sprayed with the pesticide 2,4-dichlorophenoxyacetic acid (2,4-D) at 1 and 10 times the manufacturer's recommended application concentration. The biomass was then dried overnight, burned in an open burn test facility, and emission samples were collected, analyzed, and compared against emission samples from burning untreated biomass. Blank tests and analysis of PCDD/F in the raw biomass were also performed. Emission results from burning a water-sprayed control show a ～20-fold increase in PCDD/F levels above that of the raw biomass alone, implicating combustive formation versus simple volatilization. Results from burns of pine branches sprayed with pesticide showed a statistically significant increase in the PCDD/F TEQ emissions when burning biomass at ten times the recommended pesticide concentration (from 0.22 to 1.14 ng TEQ/kg carbon burned (C(b)), both ND = 0). Similarly, a 150-fold increase in the total PCDD/F congener mass (tetra- to octa-chlorinated D/F) above that of the control was observed (from 52 to 7800 ng/kg C(b)), confirming combustive formation of PCDD/F from 2,4-D. More replicate testing is needed to evaluate effects at lower pesticide concentrations.     

Estimation of atmospheric emissions of six semivolatile polycyclic aromatic hydrocarbons in southern canada and the United States by use of an emissions processing system

Polycyclic aromatic hydrocarbons (PAHs) are toxic compounds that are ubiquitous in the atmospheric environment. The input for an emissions processing system that was originally configured forthe study of criteria air pollutants was updated to calculate emissions of six semivolatile PAHs. The goal of the work was to produce emissions estimates with the spatial and temporal resolution needed to serve as input to a regional air quality model for southern Canada and the U.S. Such modeling is helpful in determining reductions in PAH emissions that may be necessary to protect human and ecosystem health. The total annual emission of the six PAHs (sigma6PAH) for both countries was estimated at 18 273 Mg/year. A total of 90% of these emissions arise from U.S. sources. The top six source types account for 73% of emissions and are related to metal production, open burning, incineration, and forest fires. The emission factors used in this study were derived from published compilations. Although this approach has the advantage of quality control during the compilation process, some compilations include factors from older studies that may overestimate emissions since they do not account for recent improvements in emission control technology. When compared to estimates published in the National Emissions Inventory (NEI) for 2002, the U.S. emissions in this study are higher by a factor of 4 (16 424 vs 4102 Mg/year). The cause of this difference has been investigated, and much of it is likely due to our use of data unavailable in the 2002 NEI but inferred here on the basis of the PAH emissions literature. Augmenting the 2002 NEI with this additional information would bring its reported annual emissions to 8213 Mg/year, which is within a factor of 2 of the estimates herein. The results presented for southern Canada are the first published values for all known PAH sources in that country.     

PCDD and PCDF emissions from simulated sugarcane field burning

The emissions from simulated sugarcane (Saccharum officinarum) field burns were sampled and analyzed for polychlorinated dibenzodioxins and dibenzofurans (PCDDs and PCDFs). Sugarcane leaves from Hawaii and Florida were burned in a manner simulating the natural physical dimensions and biomass density found during the practice of preharvest field burning. Eight composite burn tests consisting of 3-33 kg of biomass were conducted, some with replicate samplers. Emission factor calculations using sampled concentration and measured mass loss compared well to rigorous carbon balance methods commonly used in field sampling. The two sources of sugarcane had distinctive emission levels, as did tests on separate seasonal gatherings of the Florida sugarcane. The average emission factor for two tests of Hawaii sugarcane was 253 ng toxic equivalents (TEQ)/kg of carbon burned (ng TEQ/kg(Cb)) (rsd = 16%) and for two gatherings of Florida sugarcane was 25 ng TEQ/kg(Cb) (N = 4, rsd = 50%) and 5 ng TEQ/kg(Cb) (N = 2, rsd = 91%). The Hawaii sugarcane, as well as most of the Florida sugarcane, had emission values which were well above the value of 5 ng TEQ/kg(Cb) commonly attributed to biomass combustion. Application of this emission factor range to the amount of U.S. sugarcane fields burned suggests that this practice may be a relatively minor source of PCDDs and PCDFs in the U.S. national inventory, but the limited sample size and range of results make this conclusion tenuous.     

Effect of moisture, charge size, and chlorine concentration on PCDD/F emissions from simulated open burning of forest biomass

Loblolly pine (Pinus taeda) was combusted at different charge sizes, fuel moisture, and chlorine content to determine the effect on emissions of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDDs/Fs) as well as copollutants CO, PM, and total hydrocarbons. The experiments were performed in an enclosed chamber under conditions simulating open, prescribed burns of forest biomass. Burn progress was monitored through on line measurement of combustion gases and temperature while PCDD/F concentrations were determined by ambient sampling methods. PCDD/F toxic equivalency (TEQ) and total (tetra- to octa-CDD/F) emission factors were independent of charge size (1-10 kg) and moisture content (7-50%). However, the lower chlorinated, mono- to tri-CDD/F compounds were increased by poor combustion conditions: combustion efficiency lower than 0.919 was generally found when the moisture content was higher than 30%. The increase of fuel matrix chlorine from 0.04% to 0.8% using a brine bath resulted in about a 100-fold increase of PCDD/F to about 90 ng TEQ/kg of carbon burned, C(b). These emission factors were linearly dependent on Cl concentration in the biomass. PCDD 2,3,7,8-Cl-substituted congeners and homologue patterns were also influenced by the addition of chlorine resulting in emissions with a higher abundance of the most toxic congeners (TeCDD and PeCDD). When both chlorine and moisture content were increased in the fuel, a simultaneous effect of the two parameters was observed. The increased TEQ values expected from higher Cl concentrations were mitigated by the presence of water, giving MCE = 0.868, promoting formation of mono- to tri-PCDD/F, and lowering the TEQ value. Open burn simulations were used to study PCDD/F formation in different combustion conditions providing a mathematical correlation between PCDD/F emissions and chlorine and moisture content in the fuel.     

Emission factors for carbonaceous particles and polycyclic aromatic hydrocarbons from residential coal combustion in China

Emission factors of carbonaceous particles, including black carbon (BC) and organic carbon (OC), and polycyclic aromatic hydrocarbons (PAHs) were determined for five coals, which ranged in maturity from sub-bituminous to anthracite. They were burned in the form of honeycomb briquettes in a residential coalstove, one of the most common fuel/stove combinations in China. Smoke samples were taken through dilution sampling equipment, with a high volume sampler that could simultaneously collect emissions in both particulate and gaseous phases, and a cascade impactor that could segregate particles into six fractions. Particulate BC and OC were analyzed by a thermal-optical method, and PAHs in emissions of both phases were analyzed by GC-MS. Burning of bituminous coals produced the highest emission factors of particulate matter (12.91 g/kg), BC (0.28 g/kg), OC (7.82 g/kg), and 20 PAHs (210.6 mg/kg) on the basis of burned dry ash-free (daf) coal, while the anthracite honeycomb-briquette was the cleanest household coal fuel. The size-segregated results show that more than 94% of the particles were submicron, and calculated mass median aerodynamic diameters (MMAD) of all particles were under 0.3 microm. Based on the coal consumption in the residential sector of China, 290.24 Gg (gigagrams) of particulate matter, 5.36 Gg of BC, 170.33 Gg of OC, and 4.72 Gg of 20 PAHs mass were emitted annually from household honeycomb-briquette burning during 2000. Anthracite coal should be selected preferentially and more advanced burning conditions should be applied in domestic combustion, from the viewpoint of both climate change and adverse health effects.     

Molecular characteristics of urban organic aerosols from Nanjing: a case study of A mega-city in China

Over 90 organic species have been determined in fine aerosols (PM2.5) collected during the summer and winter in Nanjing, a typical mega-city in China, using gas chromatography-mass spectrometry. The organic compounds detected were apportioned to four emission sources (i.e., plant emission, fossil fuel combustion, biomass burning, and soil resuspension) and secondary oxidation products. The most abundant classes of compounds are fatty acids, followed by sugars, dicarboxylic acids excluding oxalic and malonic acids, and n-alkanes, while alcohols, polyols/polyacids and lignin/sterols are less abundant. Total amounts of the seven classes of compounds were on average 938 ng m(-3) in the summer and 1301 ng m(-3) in the winter, respectively, contributing 0.26-1.96% of particle mass (PM2.5). In the summer, n-alkanes were heavily enhanced by vegetation emissions with a maximum carbon number (Cmax) at C29, whereas they were dominated by emissions from fossil fuels combustion with a Cmax at C22/ C23 in the winter. Concentrations of unsaturated fatty acids were lower in the summer than in the winter, being consistent with enhanced photooxidation of unsaturated fatty acids in the summer. Concentrations of dicarboxylic acids for the summer aerosols were much higher in the daytime than in the nighttime, indicating increased photochemical production in the daytime. In the summer, plant emissions were the most significant source of organic aerosols, contributing more than 33% of total compound mass (TCM), followed by fossil fuel combustion or secondary oxidation. In contrast, fossil fuel combustion was the dominant source of winter organic aerosols, contributing more than 51% of TCM, followed by plant emissions and secondary oxidation products. The quantitative results on sugars and lignin pyrolysis products further suggested that biomass burning and soil resuspension are also significant sources of urban organic aerosols.     

Air quality impacts from prescribed forest fires under different management practices

Large amounts of air pollutants are emitted during prescribed forest fires. Such emissions and corresponding air quality impacts can be modulated by different forest management practices. The impacts of changing burning seasons and frequencies and of controlling emissions during smoldering on regional air quality in Georgia are quantified using source-oriented air quality modeling, with modified emissions from prescribed fires reflecting effects of each practice. Equivalent fires in the spring and winter are found to have a greater impact on PM2.5 than those in summer, though ozone impacts are larger from spring and summer fires. If prescribed fires are less frequent more biofuel is burnt in each fire, leading to larger emissions and air quality impacts per fire. For example, emissions from a fire with a 5-year fire return interval (FRI) are 72% larger than those from a fire of the same acreage with a 2-year FRI. However, corresponding long-term regional impacts are reduced with the longer FRI since the annual burned area is reduced. Total emissions for fires in Georgia with a 5-year FRI are 32% less than those with a 2-year FRI. Smoldering emissions can lead to approximately 1.0 or 1.9 microg/m3 of PM2.5 in the Atlanta PM2.5 nonattainment area during March 2002.