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| Titel |
Coupling field and laboratory measurements to estimate the emission factors of identified and unidentified trace gases for prescribed fires |
| VerfasserIn |
R. J. Yokelson, I. R. Burling, J. B. Gilman, C. Warneke, C. E. Stockwell, J. Gouw, S. K. Akagi, S. P. Urbanski, P. Veres, J. M. Roberts, W. C. Kuster, J. Reardon, D. W. T. Griffith, T. J. Johnson, S. Hosseini, J. W. Miller, D. R. Cocker III, H. Jung, 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 ; 13, no. 1 ; Nr. 13, no. 1 (2013-01-07), S.89-116 |
| Datensatznummer |
250011717
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| Publikation (Nr.) |
 copernicus.org/acp-13-89-2013.pdf |
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| Zusammenfassung |
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 (PM2.5)
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.
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 PM2.5) 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.
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 provision should be made for
the fact that they will react in the atmosphere. In addition, the total mass
of gas-phase NMOC divided by the mass of co-emitted PM2.5 averaged
about three (range ~2.0–8.7). About 35–64% of the NMOC
were likely semivolatile or of intermediate volatility. Thus, the gas-phase
NMOC represent a large reservoir of potential precursors for secondary
formation of ozone and organic aerosol. For the single lab fire in organic
soil about 28% of the emitted carbon was present as gas-phase NMOC and
~72% of the mass of these NMOC was unidentified,
highlighting the need to learn more about the emissions from smoldering
organic soils. The mass ratio of total NMOC to "NOx as NO" ranged
from 11 to 267, indicating that NOx-limited O3 production would be
common in evolving biomass burning plumes. The fuel consumption per unit
area was 7.0 ± 2.3 Mg ha−1 and 7.7 ± 3.7 Mg ha−1 for
pine-understory and semiarid shrubland prescribed fires, respectively. |
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