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- The time evolution of aerosol composition over the Mexico City plateau
The time evolution of aerosol composition over the Mexico City plateau
Auteur :
Kleinman
L. I.,
Springston
S. R.,
Daum
P. H.,
... [et al.]
Date de publication : 17/03/2008
Type : Article
Thème : Atmosphère
Couverture :
Mexique
URL Article :
http://www.atmos-chem-phys.net/8/1559/2008/acp-8-1559-2008.pdfURL Source :
http://www.atmos-chem-phys.net/ 
Télécharger le document :
(2,92 MB) The time evolution of aerosol composition over the Mexico City plateau.pdfRésumé/Sommaire :
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.
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