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| Titel |
Modeling nitrous acid and its impact on ozone and hydroxyl radical during the Texas Air Quality Study 2006 |
| VerfasserIn |
B. H. Czader, B. Rappenglück, P. Percell, D. W. Byun, F. Ngan, S. Kim |
| 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. 15 ; Nr. 12, no. 15 (2012-08-02), S.6939-6951 |
| Datensatznummer |
250011363
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| Publikation (Nr.) |
 copernicus.org/acp-12-6939-2012.pdf |
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| Zusammenfassung |
| Nitrous acid (HONO) mixing ratios for the Houston metropolitan area were
simulated with the Community Multiscale Air Quality (CMAQ) Model for an
episode during the Texas Air Quality Study (TexAQS) II in August/September
2006 and compared to in-situ MC/IC (mist-chamber/ion chromatograph) and long
path DOAS (Differential Optical Absorption Spectroscopy) measurements at
three different altitude ranges. Several HONO sources were accounted for in
simulations, such as gas phase formation, direct emissions, nitrogen dioxide
(NO2) hydrolysis, photo-induced formation from excited NO2 and
photo-induced conversion of NO2 into HONO on surfaces covered with
organic materials. Compared to the gas-phase HONO formation there was about
a tenfold increase in HONO mixing ratios when additional HONO sources were
taken into account, which improved the correlation between modeled and
measured values. Concentrations of HONO simulated with only gas phase
chemistry did not change with altitude, while measured HONO concentrations
decrease with height. A trend of decreasing HONO concentration with altitude
was well captured with CMAQ predicted concentrations when heterogeneous
chemistry and photolytic sources of HONO were taken into account.
Heterogeneous HONO production mainly accelerated morning ozone formation,
albeit slightly. Also HONO formation from excited NO2 only slightly
affected HONO and ozone (O3) concentrations. Photo-induced conversion
of NO2 into HONO on surfaces covered with organic materials turned out
to be a strong source of daytime HONO. Since HONO immediately
photo-dissociates during daytime its ambient mixing ratios were only
marginally altered (up to 0.5 ppbv), but significant increase in the
hydroxyl radical (OH) and ozone concentration was obtained. In contrast to
heterogeneous HONO formation that mainly accelerated morning ozone
formation, inclusion of photo-induced surface chemistry influenced ozone
throughout the day. |
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