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| Titel |
Chemical evolution of volatile organic compounds in the outflow of the Mexico City Metropolitan area |
| VerfasserIn |
E. C. Apel, L. K. Emmons, T. Karl, F. Flocke, A. J. Hills, S. Madronich, J. Lee-Taylor, A. Fried, P. Weibring, J. Walega, D. Richter, X. Tie, L. Mauldin, T. Campos, A. Weinheimer, D. Knapp, B. Sive, L. Kleinman, S. Springston, R. Zaveri, J. Ortega, P. Voss, D. Blake, A. Baker, C. Warneke, D. Welsh-Bon, J. Gouw, J. Zheng, R. Zhang, J. Rudolph, W. Junkermann, D. D. Riemer |
| 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. 5 ; Nr. 10, no. 5 (2010-03-08), S.2353-2375 |
| Datensatznummer |
250008174
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| Publikation (Nr.) |
 copernicus.org/acp-10-2353-2010.pdf |
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| Zusammenfassung |
The volatile organic compound (VOC) distribution in the Mexico City
Metropolitan Area (MCMA) and its evolution as it is uplifted and transported
out of the MCMA basin was studied during the 2006 MILAGRO/MIRAGE-Mex field
campaign. The results show that in the morning hours in the city center, the
VOC distribution is dominated by non-methane hydrocarbons (NMHCs) but with a
substantial contribution from oxygenated volatile organic compounds (OVOCs),
predominantly from primary emissions. Alkanes account for a large part of
the NMHC distribution in terms of mixing ratios. In terms of reactivity,
NMHCs also dominate overall, especially in the morning hours. However, in
the afternoon, as the boundary layer lifts and air is mixed and aged within
the basin, the distribution changes as secondary products are formed. The
WRF-Chem (Weather Research and Forecasting with Chemistry) model and MOZART
(Model for Ozone and Related chemical Tracers) were able to approximate the
observed MCMA daytime patterns and absolute values of the VOC OH reactivity.
The MOZART model is also in agreement with observations showing that NMHCs
dominate the reactivity distribution except in the afternoon hours. The
WRF-Chem and MOZART models showed higher reactivity than the experimental
data during the nighttime cycle, perhaps indicating problems with the
modeled nighttime boundary layer height.
A northeast transport event was studied in which air originating in the MCMA
was intercepted aloft with the Department of Energy (DOE) G1 on 18 March and
downwind with the National Center for Atmospheric Research (NCAR) C130 one
day later on 19 March. A number of identical species measured aboard each
aircraft gave insight into the chemical evolution of the plume as it aged
and was transported as far as 1000 km downwind; ozone was shown to be
photochemically produced in the plume. The WRF-Chem and MOZART models were
used to examine the spatial extent and temporal evolution of the plume and
to help interpret the observed OH reactivity. The model results generally
showed good agreement with experimental results for the total VOC OH
reactivity downwind and gave insight into the distributions of VOC chemical
classes. A box model with detailed gas phase chemistry (NCAR Master
Mechanism), initialized with concentrations observed at one of the ground
sites in the MCMA, was used to examine the expected evolution of specific
VOCs over a 1–2 day period. The models clearly supported the experimental
evidence for NMHC oxidation leading to the formation of OVOCs downwind,
which then become the primary fuel for ozone production far away from the
MCMA. |
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