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| Titel |
Impacts of electronically photo-excited NO2 on air pollution in the South Coast Air Basin of California |
| VerfasserIn |
J. J. Ensberg, M. Carreras-Sospedra, D. Dabdub |
| 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 ; 10, no. 3 ; Nr. 10, no. 3 (2010-02-03), S.1171-1181 |
| Datensatznummer |
250008036
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| Publikation (Nr.) |
 copernicus.org/acp-10-1171-2010.pdf |
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| Zusammenfassung |
A new path for hydroxyl radical formation via photo-excitation of nitrogen
dioxide (NO2) and the reaction of photo-excited NO2 with water is
evaluated using the UCI-CIT model for the South Coast Air Basin of
California (SoCAB). Two separate studies predict different reaction rates,
which differ by nearly an order of magnitude, for the reaction of
photo-excited NO2 with water. Impacts of this new chemical mechanism on
ozone and particulate matter formation, while utilizing both reaction rates,
are quantified by simulating two summer episodes. First, sensitivity
simulations are conducted to evaluate the uncertainty in the rate of
reaction of photo-excited NO2 with water reported in the literature.
Results indicate that the addition of photo-excited NO2 chemistry
increases peak 8-h average ozone and particulate matter concentrations.
The importance of this new chemistry is then evaluated in the context of
pollution control strategies. A series of simulations are conducted to
generate isopleths for ozone and particulate matter concentrations, varying
baseline nitrogen oxides (NOx) and volatile organic compounds (VOC)
emissions. Isopleths are obtained using 1987 emissions, to represent past
conditions, and 2005, to represent current conditions in the SoCAB. Results
show that the sensitivity of modeled pollutant control strategies due to
photoexcitation decreases with the decrease in baseline emissions from 1987
to 2005. Results show that including NO2 photo-excitation, increases
the sensitivity of ozone concentration with respect to changes in NOx
emissions for both years. In particular, decreasing NOx emissions in
2005 when NO2 photo-excitation is included, while utilizing the higher
reaction rate, leads to ozone relative reduction factors that are 15%
lower than in a case without photo-excited NO2. This implies that
photoexcitation increases the effectiveness in reducing ozone through
NOx emissions reductions alone, which has implications for the
assessment of future emission control strategies. However, there is still
disagreement with respect to the reaction rate constant for the formation of
OH. Therefore, further studies are required to reduce the uncertainty in the
reaction rate constant before this new mechanism is fully implemented in
regulatory applications. |
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