Using the Atlanta metropolitan area as a case study, we examine the effects of urbanization and its associated heat island on urban ozone concentrations. Air quality data from Atlanta suggest that urban ozone concentrations are enhanced by increases in abient temperature. Model calculations suggest that this enhancement is caused by the effect of temperature on the atmospheric chemistry of peroxyacetyl nitrate (PAN), as well as the temperature dependence of natural and anthropogenic hydrocarbon emissions. A comparison of summertime temperatures in Atlanta and a nearby rural station, suggests that Atlanta's temperature over the past 15 years has increased by about 2¿ C due to urbanization and its concomitant intensification of the urban heat island. Numerical simulations using conditions of a typical summertime day in Atlanta suggest that this rise in temperature could have, (1.) resulted in a significant increase in the net emissions of natural hydrocarbons in the area in spite of the loss of about 20% of the area's forests over the same period, and (2.) negated the beneficial effects on summertime ozone oncentrations that would have been obtained from a 50% reduction in anthropogenic hydrocarbon emissions. Because a NOx-based ozone abatement strategy appears to be less sensitive to temperature than does a hydrocarbon-based strategy, a NOx strategy may prove to be more effective in the future if temperatures continue to rise as a result of urbanization and the ''greenhouse effect''. ¿American Geophysical Union 1990