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| Titel |
The time evolution of aerosol composition over the Mexico City plateau |
| VerfasserIn |
L. I. Kleinman, S. R. Springston, P. H. Daum, Y.-N. Lee, L. J. Nunnermacker, G. I. Senum, J. Wang, J. Weinstein-Lloyd, M. L. Alexander, J. Hubbe, J. Ortega, M. R. Canagaratna, J. Jayne |
| 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 ; 8, no. 6 ; Nr. 8, no. 6 (2008-03-17), S.1559-1575 |
| Datensatznummer |
250005924
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| Publikation (Nr.) |
 copernicus.org/acp-8-1559-2008.pdf |
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| Zusammenfassung |
| The time evolution of aerosol concentration and chemical composition in a
megacity urban plume was determined based on 8 flights of the DOE G-1
aircraft in and downwind of Mexico City during the March 2006 MILAGRO field
campaign. A series of selection criteria are imposed to eliminate data
points with non-urban emission influences. Biomass burning has urban and
non-urban sources that are distinguished on the basis of CH3CN and CO.
In order to account for dilution in the urban plume, aerosol concentrations
are normalized to CO which is taken as an inert tracer of urban emission,
proportional to the emissions of aerosol precursors. Time evolution is
determined with respect to photochemical age defined as −Log10
(NOx/NOy). The geographic distribution of photochemical age and CO
is examined, confirming the picture that Mexico City is a source region and
that pollutants become more dilute and aged as they are advected towards T1
and T2, surface sites that are located at the fringe of the City and 35 km
to the NE, respectively. Organic aerosol (OA) per ppm CO is found to
increase 7 fold over the range of photochemical ages studied, corresponding
to a change in NOx/NOy from nearly 100% to 10%. In the older
samples the nitrate/CO ratio has leveled off suggesting that evaporation and
formation of aerosol nitrate are in balance. In contrast, OA/CO increases
with age in older samples, indicating that OA is still being formed. The
amount of carbon equivalent to the deduced change in OA/CO with age is 56 ppbC
per ppm CO. At an aerosol yield of 5% and 8% for low and high
yield aromatic compounds, it is estimated from surface hydrocarbon
observations that only ~9% of the OA formation can be accounted
for. A comparison of OA/CO in Mexico City and the eastern U.S. gives no
evidence that aerosol yields are higher in a more polluted environment. |
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