Robert J. Yokelson

Comprehensive laboratory measurements of biomass‐burning emissions: 1. Emissions from Indonesian, African, and other fuels

Trace gas and particle emissions were measured from 47 laboratory fires burning 16 regionally to globally significant fuel types. Instrumentation included the following: open-path Fourier transform infrared spectroscopy; proton transfer reaction mass spectrometry; filter sampling with subsequent analysis of particles with diameter <2.5 μm for organic and elemental carbon and other elements; and canister sampling with subsequent analysis by gas chromatography (GC)/flame ionization detector, GC/electron capture detector, and GC/mass spectrometry. The emissions of 26 compounds are reported by fuel type. The results include the first detailed measurements of the emissions from Indonesian fuels. Carbon dioxide, CO, CH 4 , NH 3 , HCN, methanol, and acetic acid were the seven most abundant emissions (in order) from burning Indonesian peat. Acetol (hydroxyacetone) was a major, previously unobserved emission from burning rice straw (21-34 g/kg). The emission factors for our simulated African fires are consistent with field data for African fires for compounds measured in both the laboratory and the field. However, the higher concentrations and more extensive instrumentation in this work allowed quantification of at least 10 species not previously quantified for African field fires (in order of abundance): acetaldehyde, phenol, acetol, glycolaldehyde, methylvinylether, furan, acetone, acetonitrile, propenenitrile, and propanenitrile. Most of these new compounds are oxygenated organic compounds, which further reinforces the importance of these reactive compounds as initial emissions from global biomass burning. A few high-combustion-efficiency fires emitted very high levels of elemental (black) carbon, suggesting that biomass burning may produce more elemental carbon than previously estimated.

Emissions from smoldering combustion of biomass measured by open-path Fourier transform infrared spectroscopy

Biomass samples from a diverse range of ecosystems were burned in the Intermountain Fire Sciences Laboratory open combustion facility. Midinfrared spectra of the nascent emissions were acquired at several heights above the fires with a Fourier transform infrared spectrometer (FTIR) coupled to an open multipass cell. In this report, the results from smoldering combustion during 24 fires are presented including production of carbon dioxide, carbon monoxide, methane, ethene, ethyne, propene, formaldehyde, 2-hydroxyethanal, methanol, phenol, acetic acid, formic acid, ammonia, hydrogen cyanide, and carbonyl sulfide. These were the dominant products observed, and many have significant influence on atmospheric chemistry at the local, regional, and global scale. Included in these results are the first optical, in situ measurements of smoke composition from fires in grasses, hardwoods, and organic soils. About one half of the detected organic emissions arose from fuel pyrolysis which produces white smoke rich in oxygenated organic compounds. These compounds deserve more attention in the assessment of fire impacts on the atmosphere. The compound 2-hydroxyethanal is a significant component of the smoke, and it is reported here for the first time as a product of fires. Most of the observed alkane and ammonia production accompanied visible glowing combustion. NH3 is normally the major nitrogen-containing emission detected from smoldering combustion of biomass, but from some smoldering organic soils, HCN was dominant. Tar condensed on cool surfaces below the fires accounting for ∼1% of the biomass burned, but it was enriched in N by a factor of 6–7 over the parent material, and its possible role in postfire nutrient cycling should be further investigated.

Emissions of formaldehyde, acetic acid, methanol, and other trace gases from biomass fires in North Carolina measured by airborne Fourier transform infrared spectroscopy

Biomass burning is an important source of many trace gases in the global troposphere. We have constructed an airborne trace gas measurement system consisting of a Fourier transform infrared spectrometer (FTIR) coupled to a “flow-through” multipass cell (AFTIR) and installed it on a U.S. Department of Agriculture Forest Service King Air B-90. The first measurements with the new system were conducted in North Carolina during April 1997 on large, isolated biomass fire plumes. Simultaneous measurements included Global Positioning System (GPS); airborne sonde; particle light scattering, CO, and CO2; and integrated filter and canister samples. AFTIR spectra acquired within a few kilometers of the fires yielded excess mixing ratios for 10 of the most common trace gases in the smoke: water, carbon dioxide, carbon monoxide, methane, formaldehyde, acetic acid, formic acid, methanol, ethylene, and ammonia. Emission ratios to carbon monoxide for formaldehyde, acetic acid, and methanol were each 2.5±1%. This is in excellent agreement with (and confirms the relevance of) our results from laboratory fires. However, these ratios are significantly higher than the emission ratios reported for these compounds in some previous studies of “fresh” smoke. We present a simple photochemical model calculation that suggests that oxygenated organic compounds should be included in the assessment of ozone formation in smoke plumes. Our measured emission factors indicate that biomass fires could account for a significant portion of the oxygenated organic compounds and HOx present in the tropical troposphere during the dry season. Our fire measurements, along with recent measurements of oxygenated biogenic emissions and oxygenated organic compounds in the free troposphere, indicate that these rarely measured compounds play a major, but poorly understood, role in the HOx, NOx, and O3 chemistry of the troposphere.

Measurements of excess O3, CO2, CO, CH4, C2H4, C2H2, HCN, NO, NH3, HCOOH, CH3COOH, HCHO, and CH3OH in 1997 Alaskan biomass burning plumes by airborne Fourier transform infrared spectroscopy (AFTIR).

We used an airborne Fourier transform infrared spectrometer (AFTIR), coupled to a flow-through, air-sampling cell, on a King Air B-90 to make in situ trace gas measurements in isolated smoke plumes from four, large, boreal zone wildfires in interior Alaska during June 1997. AFTIR spectra acquired near the source of the smoke plumes yielded excess mixing ratios for 13 of the most common trace gases: water, carbon dioxide, carbon monoxide, methane, nitric oxide, formaldehyde, acetic acid, formic acid, methanol, ethylene, acetylene, ammonia and hydrogen cyanide. Emission ratios to carbon monoxide for formaldehyde, acetic acid, and methanol were 2.2±0.4%, 1.3±0.4%, and 1.4±0.1%, respectively. For each oxygenated organic compound, a single linear equation fits our emission factors from Alaska, North Carolina, and laboratory fires as a function of modified combustion efficiency (MCE). A linear equation for predicting the NH3/NOx emission ratio as a function of MCE fits our Alaskan AFTIR results and those from many other studies. AFTIR spectra collected in downwind smoke that had aged 2.2±1 hours in the upper, early plume yielded ΔO3/ΔCO ratios of 7.9±2.4% resulting from O3 production rates of ∼50 ppbv h−1. The ΔNH3/ΔCO ratio in another plume decreased to 1/e of its initial value in ∼2.5 hours. A set of average emission ratios and emission factors for fires in Alaskan boreal forests is derived. We estimate that the 1997 Alaskan fires emitted 46±11 Tg of CO2.

Evolution of gases and particles from a savanna fire in South Africa

average OH concentration in the plume was � 1.7 � 10 7 molecules cm � 3 . Excess CN, normalized by excess CO, decreased rapidly during the first � 5 min of aging, probably due to coagulation, and then increased, probably due to gas-to-particle conversion. The CO-normalized concentrations of particles 1.5 mm diameter increased, with smoke age. The spectral depletion of solar radiation by the smoke is depicted. The downwelling UV flux near the vertical center of the plume was about two-thirds of that near the top of the plume. INDEX TERMS: 0315 Atmospheric Composition and Structure: Biosphere/atmosphere interactions; 0317 Atmospheric Composition and Structure: Chemical kinetic and photochemical properties; 0322 Atmospheric Composition and Structure: Constituent sources and sinks; 0345 Atmospheric Composition and Structure: Pollution—urban and regional (0305); 3374 Meteorology and Atmospheric Dynamics: Tropical meteorology; KEYWORDS: gases, particles, biomass fires, smoke, savanna fires, evolution of smoke

Trace gas and particle emissions from fires in large diameter and belowground biomass fuels

[1] We adopt a working definition of residual smoldering combustion (RSC) as biomass combustion that produces emissions that are not lofted by strong fire-induced convection. RSC emissions can be produced for up to several weeks after the passage of a flame front and they are mostly unaffected by flames. Fuels prone to RSC include downed logs, duff, and organic soils. Limited observations in the tropics and the boreal forest suggest that RSC is a globally significant source of emissions to the troposphere. This source was previously uncharacterized. We measured the first emission factors (EF) for RSC in a series of laboratory fires and in a wooded savanna in Zambia, Africa. We report EFRSC for both particles with diameter <2.5 mm (PM2.5) and the major trace gases as measured by open-path Fourier transform infrared (OP-FTIR) spectroscopy. The major trace gases include carbon dioxide, carbon monoxide, methane, ethane, ethene, acetylene, propene, formaldehyde, methanol, acetic acid, formic acid, glycolaldehyde, phenol, furan, ammonia, and hydrogen cyanide. We show that a model used to predict trace gas EF for fires in a wide variety of aboveground fine fuels fails to predict EF for RSC. For many compounds, our EF for RSC-prone fuels from the boreal forest and wooded savanna are very different from the EF for the same compounds measured in fire convection columns above these ecosystems. We couple our newly measured EFRSC with estimates of fuel consumption by RSC to refine emission estimates for fires in the boreal forest and wooded savanna. We find some large changes in estimates of biomass fire emissions with the inclusion of RSC. For instance, the wooded savanna methane EF increases by a factor of 2.5 even when RSC accounts for only 10% of fuel consumption. This shows that many more measurements of fuel consumption and EF for RSC are needed to improve estimates of biomass burning emissions. INDEX TERMS: 0345 Atmospheric Composition and Structure: Pollution—urban and regional (0305); 0368 Atmospheric Composition and Structure: Troposphere—constituent transport and chemistry; 0394 Atmospheric Composition and Structure: Instruments and techniques; 0365 Atmospheric Composition and Structure: Troposphere—composition and chemistry; KEYWORDS: biomass burning, smoldering combustion, oxygenated organic compounds, ammonia, methanol, smoke Citation: Bertschi, I., R. J. Yokelson, D. E. Ward, R. E. Babbitt, R. A. Susott, J. G. Goode, and W. M. Hao, Trace gas and particle emissions from fires in large diameter and belowground biomass fuels, J. Geophys. Res., 108(D13), 8472, doi:10.1029/2002JD002100, 2003.

The tropical forest and fire emissions experiment: Emission, chemistry, and transport of biogenic volatile organic compounds in the lower atmosphere over Amazonia

(7.8 ± 2.3 mg/m 2 /h) and monoterpene fluxes (1.2 ± 0.5 mg/m 2 /h) compared well between ground and airborne measurements and are higher than fluxes estimated in this region during other seasons. The biogenic emission model, Model of Emissions of Gases and Aerosols from Nature (MEGAN), estimates fluxes that are within the model and measurement uncertainty and can describe the large observed variations associated with land-use change in the region north-west of Manaus. Isoprene and monoterpenes accounted for � 75% of the total OH reactivity in this region and are important volatile organic compounds (VOCs) for modeling atmospheric chemistry in Amazonia. The presence of fair weather clouds (cumulus humilis) had an important impact on the vertical distribution and chemistry of VOCs through the planetary boundary layer (PBL), the cloud layer, and the free troposphere (FT). Entrainment velocities between 10:00 and 11:30 local time (LT) are calculated to be on the order of 8–10 cm/s. The ratio of methyl-vinyl-ketone (MVK) and methacrolein (MAC) (unique oxidation products of isoprene chemistry) with respect to isoprene showed a pronounced increase in the cloud layer due to entrainment and an increased oxidative capacity in broken cloud decks. A decrease of the ratio in the lower free troposphere suggests cloud venting through activated clouds. OH modeled in the planetary boundary layer using a photochemical box model is much lower than OH calculated from a mixed layer budget approach. An ambient reactive sesquiterpene mixing ratio of 1% of isoprene would be sufficient to explain most of this discrepancy. Increased OH production due to increased photolysis in the cloud layer balances the low OH values modeled for the planetary boundary layer. The intensity of segregation (Is) of isoprene and OH, defined as a relative reduction of the reaction rate constant due to incomplete mixing, is found to be significant: up to 39 ± 7% in the � 800-m-deep cloud layer. The effective reaction rate between isoprene and OH can therefore vary significantly in certain parts of the lower atmosphere.

Isocyanic acid in the atmosphere and its possible link to smoke-related health effects

We measured isocyanic acid (HNCO) in laboratory biomass fires at levels up to 600 parts per billion by volume (ppbv), demonstrating that it has a significant source from pyrolysis/combustion of biomass. We also measured HNCO at mixing ratios up to 200 pptv (parts-per-trillion by volume) in ambient air in urban Los Angeles, CA, and in Boulder, CO, during the recent 2010 Fourmile Canyon fire. Further, our measurements of aqueous solubility show that HNCO is highly soluble, as it dissociates at physiological pH. Exposure levels > 1 ppbv provide a direct source of isocyanic acid and cyanate ion (NCO-) to humans at levels that have recognized health effects: atherosclerosis, cataracts, and rheumatoid arthritis, through the mechanism of protein carbamylation. In addition to the wildland fire and urban sources, we observed HNCO in tobacco smoke, HNCO has been reported from the low-temperature combustion of coal, and as a by-product of urea-selective catalytic reduction (SCR) systems that are being phased-in to control on-road diesel NOx emissions in the United States and the European Union. Given the current levels of exposure in populations that burn biomass or use tobacco, the expected growth in biomass burning emissions with warmer, drier regional climates, and planned increase in diesel SCR controls, it is imperative that we understand the extent and effects of this HNCO exposure.

Global Emissions of Trace Gases, Particulate Matter, and Hazardous Air Pollutants from Open Burning of Domestic Waste

The open burning of waste, whether at individual residences, businesses, or dump sites, is a large source of air pollutants. These emissions, however, are not included in many current emission inventories used for chemistry and climate modeling applications. This paper presents the first comprehensive and consistent estimates of the global emissions of greenhouse gases, particulate matter, reactive trace gases, and toxic compounds from open waste burning. Global emissions of CO2 from open waste burning are relatively small compared to total anthropogenic CO2; however, regional CO2 emissions, particularly in many developing countries in Asia and Africa, are substantial. Further, emissions of reactive trace gases and particulate matter from open waste burning are more significant on regional scales. For example, the emissions of PM10 from open domestic waste burning in China is equivalent to 22% of Chinas total reported anthropogenic PM10 emissions. The results of the emissions model presented here suggest that emissions of many air pollutants are significantly underestimated in current inventories because open waste burning is not included, consistent with studies that compare model results with available observations.

Trace gas emissions from laboratory biomass fires measured by open-path Fourier transform infrared spectroscopy : Fires in grass and surface fuels

The trace gas emissions from six biomass fires, including three grass fires, were measured using a Fourier transform infrared (FTIR) spectrometer coupled to an open-path, multipass cell (OP-FTIR). The quantified emissions consisted of carbon dioxide, nitric oxide, water vapor, carbon monoxide, methane, ammonia, ethylene, acetylene, isobutene, methanol, acetic acid, formic acid, formaldehyde, and hydroxyacetaldehyde. By including grass fires in this study we have now measured smoke composition from fires in each major vegetation class. The emission ratios of the oxygenated compounds, formaldehyde, methanol, and acetic acid, were 1–2% of CO in the grass fires, similar to our other laboratory and field measurements but significantly higher than in some other studies. These oxygenated compounds are important, as they affect O3 and HOx chemistry in both biomass fire plumes and the free troposphere. The OP-FTIR data and the simultaneously collected canister data indicated that the dominant C4 emission was isobutene (C4H8) and not 1-butene. The rate constant for the reaction of isobutene with the OH radical is 60% larger than that of 1-butene. We estimate that 67±9% of the fuel nitrogen was volatilized with the major nitrogen emissions, ammonia, and nitric oxide, accounting for 22±8%.