Recent Trend in Ozone Levels in the Metropolitan zone of Mexico City

Ozone concentration in the atmosphere of Mexico City is analyzed for the period 2000-2006, finding an average reduction of 24%, in spite of not meeting the norm of 110 ppb in more than 42% of the days in Pedregal. The maximum ozone levels in the last three years were 250 ppb well above the norm of 110 ppb. The number of vehicles registered in the Federal District has increased in the period by an average of 35%. Notwithstanding the increase in vehicular fleet, improvement of air quality is ascribed to the replacement of old cars by more efficient and less contaminating new cars. To decrease even more the ozone concentration, it is suggested to decrease further the Reid Vapor Pressure of gasoline to 7.0 psia to reduce the evapora- tion of light olefins.