Control strategies for urban ozone traditionally have been based on mass reductions in volatile organic compounds (VOCs). Studies show, however, that some organic gas species (such as alkanes and alcohols) form an order of magnitude less ozone than equal mass emissions of others (such as alkenes and aldehydes). Chemically detailed photochemical models are used to assess uncertainty and variability in reactivity quantification. VOC control strategies based on relative reactivity appear to be robust with respect to nationwide variations in environmental conditions and uncertainties in the atmospheric chemistry. Control of selective organic gas species on the basis of reactivity can offer cost savings over traditional strategies.

PM, PM, precursor gas, and upper-air meteorological measurements were taken in Mexico City, Mexico, from February 23 to March 22, 1997, to understand concentrations and chemical compositions of the city's particulate matter (PM). Average 24-hr PM concentrations over the period of study at the core sites in the city were 75 H g/m. The 24-hr standard of 150 μ g/m was exceeded for seven samples taken during the study period; the maximum 24-hr concentration measured was 542 μ g/m. Nearly half of the PM was composed of fugitive dust from roadways, construction, and bare land. About 50% of the PM consisted of PM, with higher percentages during the morning hours. Organic and black carbon constituted up to half of the PM. PM concentrations were highest during the early morning and after sunset, when the mixed layers were shallow. Meteorological measurements taken during the field campaign show that on most days air was transported out of the Mexico City basin during the afternoon with little day-to-day carryover.

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