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| Titel |
Evolution of trace gases and particles emitted by a chaparral fire in California |
| VerfasserIn |
S. K. Akagi, J. S. Craven, J. W. Taylor, G. R. McMeeking, R. J. Yokelson, I. R. Burling, S. P. Urbanski, C. E. Wold, J. H. Seinfeld, H. Coe, M. J. Alvarado, D. R. Weise |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 12, no. 3 ; Nr. 12, no. 3 (2012-02-07), S.1397-1421 |
| Datensatznummer |
250010637
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| Publikation (Nr.) |
 copernicus.org/acp-12-1397-2012.pdf |
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| Zusammenfassung |
| 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; NOx;
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.
NOx 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 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. |
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