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| Titel |
Impact of updated traffic emissions on HONO mixing ratios simulated for urban site in Houston, Texas |
| VerfasserIn |
B. H. Czader, Y. Choi, X. Li, S. Alvarez, B. Lefer |
| 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. 3 ; Nr. 15, no. 3 (2015-02-05), S.1253-1263 |
| Datensatznummer |
250119389
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| Publikation (Nr.) |
 copernicus.org/acp-15-1253-2015.pdf |
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| Zusammenfassung |
| Recent measurements in Houston show that HONO traffic emissions are 1.7%
of NOx emissions, which is about twice the previously estimated value of
0.8% based on tunnel measurements in 2001. The 0.8% value is widely
used to estimate mobile emissions of HONO for air quality modeling
applications. This study applies the newly estimated HONO / NOx ratio in
the WRF–SMOKE–CMAQ modeling system and estimates the impact of higher HONO
traffic emissions on its mixing ratios. Since applied emission inventory
resulted in overestimates of NOx mixing ratios and because HONO
emissions and chemical formation depend on the magnitude of NOx, thus,
before proceeding with HONO emission modifications emissions of NOx
were adjusted to reflect current emission trends. The modeled mixing ratios
of NOx were evaluated against measured data from a number of sites in
the Houston area. Overall, the NOx mean value dropped from 11.11 ppbv
in the base case to 7.59 ppbv in the NOx-adjusted case becoming much
closer to the observed mean of 7.76 ppbv. The index of agreement (IOA) is
improved in the reduced NOx case (0.71 vs. 0.75) and the absolute mean
error (AME) is lowered from 6.76 to 4.94. The modeled mixing ratios of HONO
were evaluated against the actual observed values attained at the Moody
Tower in Houston. The model could not reproduce the morning HONO peaks when
the low HONO / NOx ratio of 0.008 was used to estimate HONO emissions.
Doubling HONO emissions from mobile sources resulted in higher mixing
ratios, and the mean value increased from 0.30 to 0.41 ppbv becoming closer
to the observed mean concentrations of 0.69 but still low; AME was slightly
reduced from 0.46 to 0.43. IOA for simulation that used the 2001 emission
values is 0.63 while for simulation with higher HONO emission it increased
to 0.70. Increased HONO emissions from mobile sources resulted in a 14%
increase in OH during morning time at the location of the Moody Tower and
3% when averaged over an urban area. The increase calculated for daytime was
7 and 1% for the Moody Tower and the urban area, respectively. The
impact on ozone was found to be marginal. This study results shed light on
the underestimated HONO and OH in the morning from global/regional chemical
transport models with the typical emission of 0.8% HONO emission out of
the total NOx emissions. |
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