Grantee Research Project Results
Final Report: The Contribution of Biomass Combustion to Ambient Fine Particle Concentrations in the United States
EPA Grant Number: R826233Title: The Contribution of Biomass Combustion to Ambient Fine Particle Concentrations in the United States
Investigators: Cass, Glen , Fine, Philip M. , Seinfeld, John
Institution: California Institute of Technology
EPA Project Officer: Hahn, Intaek
Project Period: February 1, 1998 through January 31, 2001
Project Amount: $532,642
RFA: Ambient Air Quality (1997) RFA Text | Recipients Lists
Research Category: Air Quality and Air Toxics , Air
Objective:
The objective of this research project was to quantify the contribution of biomass combustion sources to atmospheric fine particle concentrations throughout the United States. Both the spatial and seasonal variation of biomass smoke concentrations were investigated.
Summary/Accomplishments (Outputs/Outcomes):
Biomass combustion can be broadly defined as the burning of any biogenic substance excluding fossil fuels and fossil fuel products. Sources of biomass combustion include: energy conversion for cooking and heating; forest brush and weed clearing for land clearing and fire safety; agricultural, municipal, and industrial waste incineration; cigarette smoke; charcoal production; structural fires; and wildfires. The particle emissions from biomass combustion can affect the radiative properties of the atmosphere, cloud formation, visibility, and public health. Previous studies indicate that the particles emitted from biomass combustion sources are predominantly less than 2 microns in diameter, making them susceptible to inhalation and pulmonary deposition. Some of the chemical constituents of the particulate matter emitted from biomass combustion, such as polycyclic aromatic hydrocarbons (PAH), have potential toxic and/or carcinogenic effects when inhaled by living organisms.
Emissions inventories by the United States Environmental Protection Agency (USEPA) estimate that approximately 20 percent of the total annual fine particle emissions to the atmosphere come from biomass combustion sources. In some regions and during certain times of the year, this figure can be even higher. If compliance with the recently proposed USEPA fine particle standards is to be attained, biomass combustion must be accurately accounted for in all regional air pollution control strategies. Despite its significance, accurate estimates of biomass combustion emissions remain elusive. The emissions are largely unregulated and arise from diverse area-wide sources. Source-oriented methods to assess the impact of biomass combustion on ambient fine particle concentrations have traditionally combined source test emissions data with land-use, fuel consumption, and industrial or residential activity estimates to calculate pollutant emissions. Atmospheric transport models then are used to predict pollutant concentrations at downwind air sampling sites. However, these methods are limited by often inaccurate inventory estimates, limited data on emission factors, and the short time scales of transport calculations. Alternatively, receptor-based chemical mass balance models, which compare the chemical composition of fine particles emitted from the source to the chemical composition of ambient samples, can resolve the contributions of different source types to a particular ambient sample. Although black carbon, water-soluble potassium, and carbon isotope ratios have been used as indicators of biomass combustion, these tracers have other non-biomass sources, and thus are not unique to biomass combustion. The variety and abundance of individual organic compounds emitted from biomass combustion, however, provide a rich source of potential chemical tracers for use in receptor-oriented modeling studies. Some of these organic compounds are not only unique to biomass combustion but also specific to the class or species of plant material being burned.
To characterize the emissions from biomass combustion sources, an extensive series of source tests were conducted on the most important source types and fuels found in the United States. Source tests were conducted using an advanced dilution source sampling system designed by Hildemann, et al. (1989). Hot exhaust emissions from each source are diluted and cooled with clean particle-free air. Sufficient residence time allows the organic vapors to partition into the particle phase under conditions similar to those experienced in the atmosphere downwind of a source. Particles then are collected with an array of filter substrates for subsequent chemical analysis, including GC/MS for organic speciation.
The most important biomass combustion source, as determined from inventory estimates, is residential wood combustion. Therefore, the first source considered was the residential combustion of wood in fireplaces. A conventional masonry fireplace was used and exhaust was extracted from the chimney one story above the fire. Wood species selection was based on state level wood fuel consumption activity combined with forestry surveys of the most available woods within each state. Twenty-two wood species were chosen for testing, including 18 of the top 21 most commonly available wood species in the United States.
Fine particle mass emission factors from the 22 wood species tested in fireplaces ranged from 1.6 to 11.4 grams per kilogram wood burned. The fine particles consisted primarily of organic compounds, with lesser amounts of elemental carbon, ionic species, and trace elements. Elemental carbon composition of the fine particles varied widely from near 1 to more than 30 wt percent of the fine particle mass. Softwoods with visually noticeable sap inclusions and woods burned with their bark tended to emit more elemental carbon than the other wood species. The cellulose pyrolysis product, levoglucosan, was the most abundant single organic compound quantified in all of the fireplace source tests. As has been previously determined by other researchers, levoglucosan serves as a unique marker for biomass combustion in general. The emissions of levoglucosan varied from species to species within a general range of 6 to 35 percent of the total fine particle mass. Substituted syringols were emitted primarily from hardwood combustion, and resin acids were indicative of softwood smoke. Several individual organic compounds were, at least within the current testing program, unique to a particular wood species. Betulin was only found in the emissions from paper birch, juvabione and dehydrojuvabione were unique to balsam fir, friedelin was detected only in the white oak combustion emissions, and yangambin (lirioresinol dimethyl ether) was unique to the yellow poplar. Other potentially significant compounds quantified include retene from the softwoods, ß-sitosterol, the amyrins and amyrones, and several tocopherols.
The top five available wood species in the United States were burned in an iron wood stove, and sampling was performed with the same method as the fireplace tests. The wood stove included a catalytic bed designed to reduce pollutant emissions. To simulate a wood stove without emissions controls, which is still the most prevalent type in common use in the United States, the catalytic bed was not engaged for the tests of the five wood species. Two tests were repeated with the catalytic bed in operation to determine its effect on fine particle emissions. Fine particle emission factors were lower from the wood stove combustion of a given wood species than those from fireplace combustion. Elemental carbon composition of the particulate matter is generally higher from the wood stove, and even higher when the catalyst is employed, than that from the fireplace, most likely due to the different combustion conditions. In general, the same organic compounds and similar hardwood/softwood distinctions were observed in the wood stove tests as in the fireplace tests. Levoglucosan was still the most abundant organic compound present. PAH emissions were generally higher for the wood stove tests than for the fireplace tests for the same reason that elemental carbon emissions were enhanced.
Two biomass combustion source categories were considered: the prescribed burning of foliar fuels and the open burning of agricultural waste. The experiments were conducted at a burn chamber at the USEPA research facility in Research Triangle Park, NC. The dilution sampler employed for these tests was based on the Hildemann design with some improvements in automated flow control and data acquisition. Five foliar fuels from throughout the United States were selected and tested, along with two agricultural waste residues, rice straw and wheat straw. Although the fine particle emission factors from these sources were generally higher than the residential wood combustion experiments, the organic compounds detected and quantified were similar. The substituted syringol and resin acid emissions corresponded to the same hardwood/softwood distinction seen in the wood combustion. The agricultural burns produced less substituted guaiacols than the other foliar fuels and less substituted syringols than the hardwood foliage. Another notable difference was the higher emission factors of alkanoic acids and alkanes from the foliar fuel combustion due to the higher abundance of plant waxes in the foliage as opposed to the woody material. Levoglucosan was emitted from both the foliar and agricultural burns at levels comparable to the residential wood combustion tests.
Because many of the source signatures of the fuels tested are not sufficiently unique to resolve each fuel type in a chemical mass balance receptor model, composite residential wood combustion source profiles are calculated on a regional basis. The procedure is somewhat analogous to deriving fleet average emission profiles for motor vehicles. Wood species availability and wood burning activity are combined on a state-by-state basis, and then emission factors from the source tests are applied according to wood species and appliance type (fireplace vs. wood stove). Particle-phase emissions of relevant organic compounds then are totaled to give regional residential wood combustion source profiles for use in chemical mass balance calculations. A comparison of the regional profiles shows that significant differences in source signatures can be expected from region to region. The differences arise largely due to the varying hardwood and softwood availability in different parts of the United States.
Regional source profiles were calculated and compared to ambient samples collected as part of the IMPROVE and other national sampling networks. More than 50 sampling sites were examined with the filters from these sites combined into semi-annual seasonal composites prior to chemical analysis. The result of the model calculations corresponds to the primary objective of this projecta national map of the contribution of biomass combustion to ambient fine particle concentrations in the United States. The cold season showed higher contributions from biomass combustion, suggesting that residential wood combustion is a more significant source of fine particles than forest fires. The Eastern states were more geographically uniform with respect to biomass combustion contributions compared to the Western states, which showed more local variation. Three other fine particle sources (soil dust, vegetative detritus, and motor vehicles) were included in the model with results consistent with expectations (i.e., higher soil dust contribution in the desert Southwest).
Biomass combustion was shown to be a significant source of fine particle emissions to the atmosphere in many regions of the United States. The results of this study provide important information to air quality regulatory agencies that must formulate strategies to meet the recently proposed fine particle standards. Biomass combustion sources remain largely unregulated, and the results suggest that they need to be considered in regional air pollution control efforts to protect human health and improve visibility. The detailed organic compound source profiles for the most important biomass combustion sources contained in this report can be used in other source apportionment studies according to the methods presented. Future studies, in which new ambient filters are collected and analyzed, will be relatively inexpensive considering that the most important source profiles already exist and that the quantification of only a few selected organic species is necessary for chemical mass balance modeling.
Journal Articles on this Report : 6 Displayed | Download in RIS Format
Other project views: | All 12 publications | 6 publications in selected types | All 6 journal articles |
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Fine PM, Cass GR, Simoneit BRT. Chemical characterization of fine particle emissions from fireplace combustion of woods grown in the northeastern United States. Environmental Science & Technology 2001;35(13):2665-2675. |
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Fine PM, Cass GR, Simoneit BRT. Chemical characterization of fine particle emissions from the fireplace combustion of woods grown in the Southern United States. Environmental Science & Technology 2002;36(7):1442-1451. |
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Fine PM, Cass GR, Simoneit BRT. Organic compounds in biomass smoke from residential wood combustion: emissions characterization at a continental scale. Journal of Geophysical Research 2002;107(D21):ICC 11-1-ICC 11-9. |
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Fine PM, Cass GR, Simoneit BRT. Chemical characterization of fine particle emissions from the wood stove combustion of prevalent United States tree species. Environmental Engineering Science 2004;21(6):705-721. |
R826233 (Final) |
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Nolte CG, Schauer JJ, Cass GR, Simoneit BRT. Highly Polar Organic Compounds Present in Wood Smoke and in the Ambient Atmosphere. Environmental Science & Technology 2001;35(10):1912-1919. |
R826233 (Final) |
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Nolte CG, Schauer JJ, Cass GR, Simoneit BRT. Trimethylsilyl derivatives of organic compounds in source samples and in atmospheric fine particulate matter. Environmental Science & Technology 2002;36(20):4273-4281. |
R826233 (Final) |
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Supplemental Keywords:
air, ambient air, atmosphere, tropospheric, particulates, organics, environmental chemistry, analytical, engineering, measurement methods, wood burning., RFA, Scientific Discipline, Air, particulate matter, Environmental Chemistry, Environmental Monitoring, ambient air quality, particulates, air toxics, chemical characteristics, fine particles, ambient measurement methods, biomass combustion, smoke concentrations, seasonal variation, organic chemical trace techniques, incinerationProgress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.