Biomass burning (BB) is a major global source of trace gases and particles. Accurately representing the production and evolution of these emissions is an important goal for atmospheric chemical transport models. We measured a suite of gases and aerosols emitted from an 81 hectare prescribed fire in chaparral fuels on the central coast of California, US on 17 November 2009. We also measured physical and chemical changes that occurred in the isolated downwind plume in the first ~4 h after emission. The measurements were carried out onboard a Twin Otter aircraft outfitted with an airborne Fourier transform infrared spectrometer (AFTIR), aerosol mass spectrometer (AMS), single particle soot photometer (SP2), nephelometer, LiCor CO₂ analyzer, a chemiluminescence ozone instrument, and a wing-mounted meteorological probe. Our measurements included: CO₂; CO; NO_x; NH₃; non-methane organic compounds; organic aerosol (OA); inorganic aerosol (nitrate, ammonium, sulfate, and chloride); aerosol light scattering; refractory black carbon (rBC); and ambient temperature, relative humidity, barometric pressure, and three-dimensional wind velocity. The molar ratio of excess O₃ to excess CO in the plume (ΔO₃/ΔCO) increased from −5.13 (±1.13) × 10⁻³ to 10.2 (±2.16) × 10⁻² in ~4.5 h following smoke emission. Excess acetic and formic acid (normalized to excess CO) increased by factors of 1.73 ± 0.43 and 7.34 ± 3.03 (respectively) over the same time since emission. Based on the rapid decay of C₂H₄ we infer an in-plume average OH concentration of 5.27 (±0.97) × 10⁶ molec cm⁻³, consistent with previous studies showing elevated OH concentrations in biomass burning plumes. Ammonium, nitrate, and sulfate all increased over the course of 4 h. The observed ammonium increase was a factor of 3.90 ± 2.93 in about 4 h, but accounted for just ~36% of the gaseous ammonia lost on a molar basis. Some of the gas phase NH₃ loss may have been due to condensation on, or formation of, particles below the AMS detection range. NO_x was converted to PAN and particle nitrate with PAN production being about two times greater than production of observable nitrate in the first ~4 h following emission. The excess aerosol light scattering in the plume (normalized to excess CO₂) increased by a factor of 2.50 ± 0.74 over 4 h. The increase in light scattering was similar to that observed in an earlier study of a biomass burning plume in Mexico where significant secondary formation of OA closely tracked the increase in scattering. In the California plume, however, ΔOA/ΔCO₂ decreased sharply for the first hour and then increased slowly with a net decrease of ~20% over 4 h. The fraction of thickly coated rBC par...

An extensive program of experiments focused on biomass burning emissions began with a laboratory phase in which vegetative fuels commonly consumed in prescribed fires were collected in the southeastern and southwestern US and burned in a series of 71 fires at the US Forest Service Fire Sciences Laboratory in Missoula, Montana. The particulate matter (PM_2.5) emissions were measured by gravimetric filter sampling with subsequent analysis for elemental carbon (EC), organic carbon (OC), and 38 elements. The trace gas emissions were measured by an open-path Fourier transform infrared (OP-FTIR) spectrometer, proton-transfer-reaction mass spectrometry (PTR-MS), proton-transfer ion-trap mass spectrometry (PIT-MS), negative-ion proton-transfer chemical-ionization mass spectrometry (NI-PT-CIMS), and gas chromatography with MS detection (GC-MS). 204 trace gas species (mostly non-methane organic compounds (NMOC)) were identified and quantified with the above instruments. Many of the 182 species quantified by the GC-MS have rarely, if ever, been measured in smoke before. An additional 153 significant peaks in the unit mass resolution mass spectra were quantified, but either could not be identified or most of the signal at that molecular mass was unaccounted for by identifiable species. <br><br> In a second, "field" phase of this program, airborne and ground-based measurements were made of the emissions from prescribed fires that were mostly located in the same land management units where the fuels for the lab fires were collected. A broad variety, but smaller number of species (21 trace gas species and PM_2.5) was measured on 14 fires in chaparral and oak savanna in the southwestern US, as well as pine forest understory in the southeastern US and Sierra Nevada mountains of California. The field measurements of emission factors (EF) are useful both for modeling and to examine the representativeness of our lab fire EF. The lab EF/field EF ratio for the pine understory fuels was not statistically different from one, on average. However, our lab EF for "smoldering compounds" emitted from the semiarid shrubland fuels should likely be increased by a factor of ~2.7 to better represent field fires. Based on the lab/field comparison, we present emission factors for 357 pyrogenic species (including unidentified species) for 4 broad fuel types: pine understory, semiarid shrublands, coniferous canopy, and organic soil. <br><br> To our knowledge this is the most comprehensive measurement of biomass burning emissions to date and it should enable improved representation of smoke composition in atmospheric models. The results support a recent estimate of global NMOC emissions from biomass burning that is much higher than widely used estimates and they provide important insights into the nature of smoke. 31–72% of the mass of gas-phase NMOC species was attributed to species that we could not identify. These unidentified species are not represented in most models, but some pr...

Abstract.A comprehensive suite of instruments was used to quantify the emissions of over 200 organic gases, including methane and volatile organic compounds (VOCs), and 9 inorganic gases from 56 laboratory burns of 18 different biomass fuel types common in the southeastern, southwestern, or northern US. A gas chromatograph-mass spectrometry (GC-MS) instrument provided extensive chemical detail of discrete air samples collected during a laboratory burn and was complemented by real-time measurements of organic and inorganic species via an open-path Fourier transform infrared spectroscopy (OP-FTIR) instrument and three different chemical ionization-mass spectrometers. These measurements were conducted in February 2009 at the US Department of Agriculture's Fire Sciences Laboratory in Missoula, Montana and were used as the basis for a number of emission factors reported by Yokelson et al. (2013). The relative magnitude and composition of the gases emitted varied by individual fuel type and, more broadly, by the three geographic fuel regions being simulated. Discrete emission ratios relative to carbon monoxide (CO) were used to characterize the composition of gases emitted by mass; reactivity with the hydroxyl radical, OH; and potential secondary organic aerosol (SOA) precursors for the 3 different US fuel regions presented here. VOCs contributed less than 0.78 % ± 0.12 % of emissions by mole and less than 0.95 % × 0.07 % of emissions by mass (on average) due to the predominance of CO 2 , CO, CH 4 , and NO x emissions; however, VOCs contributed 70-90 (±16) % to OH reactivity and were the only measured gas-phase source of SOA precursors from combustion of biomass. Over 82 % of the VOC emissions by mole were unsaturated compounds including highly reactive alkenes and aromatics and photolabile oxygenated VOCs (OVOCs) such as formaldehyde. OVOCs contributed 57-68 % of the VOC mass emitted, 41-54 % of VOC-OH reactivity, and aromaticOVOCs such as benzenediols, phenols, and benzaldehyde were the dominant potential SOA precursors. In addition, ambient air measurements of emissions from the Fourmile Canyon Fire that affected Boulder, Colorado in September 2010 allowed us to investigate biomass burning (BB) emissions in the presence of other VOC sources (i.e., urban and biogenic emissions) and identify several promising BB markers including benzofuran, 2-furaldehyde, 2-methylfuran, furan, and benzonitrile.

Abstract. Vegetation commonly managed by prescribed burning was collected from five southeastern and southwestern US military bases and burned under controlled conditions at the US Forest Service Fire Sciences Laboratory in Missoula, Montana. The smoke emissions were measured with a large suite of state-of-the-art instrumentation including an open-path Fourier transform infrared (OP-FTIR) spectrometer for measurement of gas-phase species. The OP-FTIR detected and quantified 19 gas-phase species in these fires: CO 2 , CO, CH 4 , C 2 H 2 , C 2 H 4 , C 3 H 6 , HCHO, HCOOH, CH 3 OH, CH 3 COOH, furan, H 2 O, NO, NO 2 , HONO, NH 3 , HCN, HCl, and SO 2 . Emission factors for these species are presented for each vegetation type burned. Gas-phase nitrous acid (HONO), an important OH precursor, was detected in the smoke from all fires. The HONO emission factors ranged from 0.15 to 0.60 g kg −1 and were higher for the southeastern fuels. The fire-integrated molar emission ratios of HONO (relative to NO x ) ranged from approximately 0.03 to 0.20, with higher values also observed for the southeastern fuels. The majority of non-methane organic compoundCorrespondence to: R. J. Yokelson (bob.yokelson@umontana.edu) (NMOC) emissions detected by OP-FTIR were oxygenated volatile organic compounds (OVOCs) with the total identified OVOC emissions constituting 61 ± 12% of the total measured NMOC on a molar basis. These OVOC may undergo photolysis or further oxidation contributing to ozone formation. Elevated amounts of gas-phase HCl and SO 2 were also detected during flaming combustion, with the amounts varying greatly depending on location and vegetation type. The fuels with the highest HCl emission factors were all located in the coastal regions, although HCl was also observed from fuels farther inland. Emission factors for HCl were generally higher for the southwestern fuels, particularly those found in the chaparral biome in the coastal regions of California.

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 NO x 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.