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| Titel |
Investigation of secondary formation of formic acid: urban environment vs. oil and gas producing region |
| VerfasserIn |
B. Yuan, P. R. Veres, C. Warneke, J. M. Roberts, J. B. Gilman, A. Koss, P. M. Edwards, M. Graus, W. C. Kuster, S.-M. Li, R. J. Wild, S. S. Brown, W. P. Dubé, B. M. Lerner, E. J. Williams, J. E. Johnson, P. K. Quinn, T. S. Bates, B. Lefer, P. L. Hayes, J. L. Jimenez, R. J. Weber, R. Zamora, B. Ervens, D. B. Millet, B. Rappenglück, J. A. de Gouw |
| 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 ; 15, no. 4 ; Nr. 15, no. 4 (2015-02-24), S.1975-1993 |
| Datensatznummer |
250119454
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| Publikation (Nr.) |
 copernicus.org/acp-15-1975-2015.pdf |
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| Zusammenfassung |
| Formic acid (HCOOH) is one of the most abundant carboxylic acids in the
atmosphere. However, current photochemical models cannot fully explain
observed concentrations and in particular secondary formation of formic acid
across various environments. In this work, formic acid measurements made at
an urban receptor site (Pasadena) in June–July 2010 during CalNex (California Research at the
Nexus of Air Quality and Climate Change) and a
site in an oil and gas producing region (Uintah Basin) in January–February 2013 during UBWOS 2013
(Uintah Basin Winter Ozone Studies) will be discussed. Although the VOC (volatile organic compounds) compositions
differed dramatically at the two sites, measured formic acid concentrations
were comparable: 2.3 ± 1.3 in UBWOS 2013 and 2.0 ± 1.0 ppb in CalNex.
We determine that concentrations of formic acid at both sites were dominated
by secondary formation (> 99%). A constrained box model
using the Master Chemical Mechanism (MCM v3.2) underestimates the measured
formic acid concentrations drastically at both sites (by a factor of
> 10). Compared to the original MCM model that includes only
ozonolysis of unsaturated organic compounds and OH oxidation of acetylene,
when we updated yields of ozonolysis of alkenes and included OH oxidation of
isoprene, vinyl alcohol chemistry, reaction of formaldehyde with HO2,
oxidation of aromatics, and reaction of CH3O2 with OH, the model
predictions for formic acid were improved by a factor of 6.4 in UBWOS 2013
and 4.5 in CalNex, respectively. A comparison of measured and modeled
HCOOH/acetone ratios is used to evaluate the model performance for
formic acid. We conclude that the modified chemical mechanism can explain 19
and 45% of secondary formation of formic acid in UBWOS 2013 and CalNex,
respectively. The contributions from aqueous reactions in aerosol and
heterogeneous reactions on aerosol surface to formic acid are estimated to be
0–6 and 0–5% in UBWOS 2013 and CalNex, respectively. We observe that
air–snow exchange processes and morning fog events may also contribute to
ambient formic acid concentrations during UBWOS 2013 (~ 20% in
total). In total, 53–59 in UBWOS 2013 and 50–55% in CalNex of
secondary formation of formic acid remains unexplained. More work on formic
acid formation pathways is needed to reduce the uncertainties in the sources
and budget of formic acid and to narrow the gaps between measurements and
model results. |
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