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. 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.

Abstract. In October–November 2011 we measured trace gas emission factors from seven prescribed fires in South Carolina (SC), US, using two Fourier transform infrared spectrometer (FTIR) systems and whole air sampling (WAS) into canisters followed by gas-chromatographic analysis. A total of 97 trace gas species were quantified from both airborne and ground-based sampling platforms, making this one of the most detailed field studies of fire emissions to date. The measurements include the first emission factors for a suite of monoterpenes produced by heating vegetative fuels during field fires. The first quantitative FTIR observations of limonene in smoke are reported along with an expanded suite of monoterpenes measured by WAS including α-pinene, β-pinene, limonene, camphene, 4-carene, and myrcene. The known chemistry of the monoterpenes and their measured abundance of 0.4–27.9% of non-methane organic compounds (NMOCs) and ~ 21% of organic aerosol (mass basis) suggests that they impacted secondary formation of ozone (O3), aerosols, and small organic trace gases such as methanol and formaldehyde in the sampled plumes in the first few hours after emission. The variability in the initial terpene emissions in the SC fire plumes was high and, in general, the speciation of the initially emitted gas-phase NMOCs was 13–195% different from that observed in a similar study in nominally similar pine forests in North Carolina ~ 20 months earlier. It is likely that differences in stand structure and environmental conditions contributed to the high variability observed within and between these studies. Similar factors may explain much of the variability in initial emissions in the literature. The ΔHCN/ΔCO emission ratio, however, was found to be fairly consistent with previous airborne fire measurements in other coniferous-dominated ecosystems, with the mean for these studies being 0.90 ± 0.06%, further confirming the value of HCN as a biomass burning tracer. The SC results also support an earlier finding that C3-C4 alkynes may be of use as biomass burning indicators on the time-scale of hours to a day. It was possible to measure the downwind chemical evolution of the plume on four of the fires and significant O3 formation (ΔO3/ΔCO from 10–90%) occurred in all of these plumes within two hours. The slowest O3 production was observed on a cloudy day with low co-emission of NOx. The fastest O3 production was observed on a sunny day when the downwind plume almost certainly incorporated significant additional NOx by passing over the Columbia, SC metropolitan area. Due to rapid plume dilution, it was only possible to acquire high-quality downwind data for two other trace gas species (formaldehyde and methanol) during two of the fires. In all four of these cases, significant increases in formaldehyde and methanol were observed in <2 h. This is likely the first direct observation of post-emission methanol production in biomass burning plumes. Post-emission production of methanol does not always happen in young biomass burning plumes, and its occurrence in this study could have involved terpene precursors to a significant extent.

Abstract. We have measured emission factors for 19 trace gas species and particulate matter (PM 2.5 ) from 14 prescribed fires in chaparral and oak savanna in the southwestern US, as well as conifer forest understory in the southeastern US and Sierra Nevada mountains of California. These are likely the most extensive emission factor field measurements for temperate biomass burning to date and the only published emission factors for temperate oak savanna fuels. This study helps to close the gap in emissions data available for temperate zone fires relative to tropical biomass burning. We present the first field measurements of the biomass burning emissions of glycolaldehyde, a possible precursor for aqueous phase secondary organic aerosol formation. We also measured the emissions of phenol, another aqueous phase secondary organic aerosol precursor. Our data confirm previous observations that urban deposition can impact the NO x emission factors and thus subsequent plume chemistry. For two fires, we measured both the emissions in the convective smoke plume from our airborne platform and the unlofted residual smoldering combustion emissions with our groundbased platform. The smoke from residual smoldering combustion was characterized by emission factors for hydrocarbon and oxygenated organic species that were up to ten times higher than in the lofted plume, including high 1,3-butadiene and isoprene concentrations which were not observed in the lofted plume. This should be considered in modeling the air Correspondence to: R. J. Yokelson (bob.yokelson@umontana.edu) quality impacts for smoke that disperses at ground level. We also show that the often ignored unlofted emissions can significantly impact estimates of total emissions. Preliminary evidence suggests large emissions of monoterpenes in the residual smoldering smoke. These data should lead to an improved capacity to model the impacts of biomass burning in similar temperate ecosystems.