Ozone and its precursors in the atmosphere of Mexico City

The relative apportionment of hydrocarbons (HCs) coming from mobile, fixed, and other sources (not correlated either to carbon monoxide [CO] or sul-fur dioxide [SO2] emissions as solvent evaporation and biogenic sources) is calculated as previously proposed by Riveros et al.1 through the linear ap-proximation [HC] total = [HC]0 + m1 [CO] + m2 [SO2], where m1 and m2 are fitted constants. The obtained apportionment with air samples taken in 1993 is con-sistent with the earlier published apportionment with air samples taken in 1992, validating the previous proce-dure. This analysis suggests that 75 % of HC originate IMPLICATIONS The simultaneous measurement of HC and NO2 in Mexic