Ozone and Its Precursors in the Atmosphere of Mexico City

Abstract

The relative apportionment of hydrocarbons (HCs) coming from mobile, fixed, and other sources (not correlated either to carbon monoxide [CO] or sulfur dioxide [SO 2 ] emissions as solvent evaporation and biogenic sources) is calculated as previously proposed by Riveros et al. 1 through the linear approximation [HC]where m 1 and m 2 are fitted constants.The obtained apportionment with air samples taken in 1993 is consistent with the earlier published apportionment with air samples taken in 1992, validating the previous procedure.This analysis suggests that 75% of HC originate IMPLICATIONSThe simultaneous measurement of HC and NO 2 in Mexico City's urban atmosphere was used to estimate the contribution of these two precursors to tropospheric O 3 formation.This paper shows that HC and NO 2 measurements at noon (12:00-3:00 p.m.) are better predictors of maximal O 3 concentration than measurements at the concentration peak (6:00-9:00 a.m.).This can be explained by the variable pollutant dilution associated with changes in atmospheric conditions through the day.The approach used in this work to estimate HC and NO 2 contribution to O 3 formation gives useful information to evaluate antipollution policies.from mobile sources, 5-18% from fixed sources, and 7-20% from other sources (mainly solvents and biogenic sources).A similar analysis was employed to estimate the relative contribution of HCs and nitric oxides (NO 2 ) to ozone (O 3 ) formation, the most important air pollutant in Mexico City.In this way, through a local lineation of O 3 isopleths, simultaneous measurements of HC and NO 2 in the atmosphere were fitted to the equation--to predict O 3 peak.With these data, the adjusted parameters show that NO 2 , not HC as was proposed previously, is the most important contributor to O 3 formation.