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53359 
Journal Article 
The influence of aerosols on photochemical smog in Mexico City 
Castro, T; Madronich, S; Rivale, S; Muhlia, A; Mar, B 
2001 
1 
Atmospheric Environment
ISSN: 1352-2310
EISSN: 1873-2844 
35 
10 
1765-1772 
WOS:000167745600005 
Aerosols in the Mexico City atmosphere can have a non-negligible effect on the ultraviolet radiation field and hence on the formation of photochemical smog. We used estimates of aerosol optical depths from sun photometer observations in a detailed radiative transfer model, to calculate photolysis rate coefficients (JNO2) for the key reaction NO2+hNO+O ("lambda"<430 nm). The calculated values are in good agreement with previously published measurements of JNO2at two sites in Mexico City: Palacio de MinerÝa (19░25'59'N, 99░07'58'W, 2233 masl), and IMP (19░28'48'N, 99░11'07'W, 2277 masl) and in Tres Marias, a town near Mexico City (19░03'N, 99░14'W, 2810 masl). In particular, the model reproduces very well the contrast between the two urban sites and the evidently much cleaner Tres Marias site. For the measurement days, reductions in surface JNO2 by 10-30% could be attributed to the presence of aerosols, with considerable uncertainty due largely to lack of detailed data on aerosol optical properties at ultraviolet wavelengths (esp. the single scattering albedo). The potential impact of such large reductions in photolysis rates on surface ozone concentrations is illustrated with a simple zero-dimensional photochemical model. 
photolysis rates; aerosols optical properties; photochemical smog; Mexico City