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Published February 2012 | Published + Supplemental Material
Journal Article Open

Evolution of trace gases and particles emitted by a chaparral fire in California


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 CO_2 analyzer, a chemiluminescence ozone instrument, and a wing-mounted meteorological probe. Our measurements included: CO_2; CO; NO_x; NH_3; 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 O_3 to excess CO in the plume (ΔO_3/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 C_2H_4 we infer an in-plume average OH concentration of 5.27 (±0.97) × 10^6 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 NH_3 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 CO_2) 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/ΔCO_2 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 particles increased up to ~85% over the 4 h aging period. Decreasing OA accompanied by increased scattering/particle coating in initial aging may be due to a combination of particle coagulation and evaporation processes. Recondensation of species initially evaporated from the particles may have contributed to the subsequent slow rise in OA. We compare our results to observations from other plume aging studies and suggest that differences in environmental factors such as smoke concentration, oxidant concentration, actinic flux, and RH contribute significantly to the variation in plume evolution observations.

Additional Information

© 2012 Author(s). This work is distributed under the Creative Commons Attribution 3.0 License. Received: 2 June 2011. Published in Atmos. Chem. Phys. Discuss.: 8 August 2011. Revised: 27 December 2011. Accepted: 20 January 2012. Published: 7 February 2012. Edited by: R. Cohen. We thank our pilot Scott Miller and the USFS Region 4 Twin Otter management and support team. We thank Jason McCarty and the Santa Barbara County Fire Department for carrying out the burn, fuels and weather information, and coordination with our airborne team. We thank Jose Jimenez, Doug Worsnop, and Chuck Kolb for useful discussions regarding this manuscript and Holly Eissinger for help in preparation of selected figures. Satellite imagery and analysis were provided by Mark Ruminski, NESDIS, Satellite Analysis Branch. Research modifications to the Twin Otter, specialized inlets, and upgrades to AFTIR were funded by NSF grant ATM-0513055. S. A., G. M., and R. Y. were supported in whole or part by NSF grant ATM-0936321. R. Y., J. C., I. B., and the Twin Otter flight hours were supported by the Strategic Environmental Research and Development Program (SERDP) projects SI-1648 and SI-1649 and administered through Forest Service Research Joint Venture Agreement 08JV11272166039, and we thank the sponsors for their support. Participation of the SP2 was made possible in part by a travel grant from the Royal Society and support from the UK Natural Environment Research Council.

Attached Files

Published - Akagi2012p17454Atmos_Chem_Phys.pdf

Supplemental Material - acp-12-1397-2012-supplement.pdf


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