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| Titel |
Reactive nitrogen in Mexico City and its relation to ozone-precursor sensitivity: results from photochemical models |
| VerfasserIn |
S. Sillman, J. J. West |
| 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 ; 9, no. 11 ; Nr. 9, no. 11 (2009-06-02), S.3477-3489 |
| Datensatznummer |
250007347
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| Publikation (Nr.) |
 copernicus.org/acp-9-3477-2009.pdf |
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| Zusammenfassung |
| We use results of a 3-D photochemistry/transport model for ozone formation
in Mexico City during events in 1997 to investigate ambient concentrations
of reactive nitrogen in relation to ozone-precursor sensitivity. Previous
results from other locations suggest that ratios such as O3/NOy
and H2O2/HNO3 might provide measurement-based indicators for
NOx-sensitive or VOC-sensitive conditions. Mexico City presents a
different environment due to its high concentrations of VOC and high level
of pollutants in general. The model predicts a correlation between PAN and
O3 with relatively high PAN/O3 (0.07), which is still lower than
measured values. The model PAN is comparable with results from a model for
Paris but much higher than were found in Nashville in both models and
measurements. The difference is due in part to the lower temperature in
Mexico City relative to Nashville. Model HNO3 in Mexico City is
unusually low for an urban area and PAN/HNO3 is very high, probably due
to the high ratio of reactivity-weighted VOC to NOx. The model predicts
that VOC-sensitive chemistry in Mexico is associated with high NOx,
NOy and NOx/NOy and with low O3/NOy and
H2O2/HNO3, suggesting that these indicators work well for
Mexico City. The relation between ozone-precursor sensitivity and either
O3/NOz or O3/HNO3 is more ambiguous. VOC-sensitive
conditions are associated with higher O3/HNO3 than would be found
in NOx-sensitive conditions, but model O3/HNO3 associated
with both NOx-sensitive and VOC-sensitive chemistry is higher in Mexico
than in other cities. The model predicts a mixed pattern of ozone-precursor
sensitivity
in Mexico City, with VOC-sensitive conditions in the
morning and NOx-sensitive in the afternoon, in contrast to
results from other models for more recent events that predicted strongly VOC-
sensitive
conditions throughout the day. The difference in predicted ozone-precursor
sensitivity is most
likely due to different emission rates and to changes in emissions over time.
The model with mixed
sensitivity predicts much lower ambient NOx and NOx/NOy than
the strongly VOC-sensitive model. |
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