Climate change and urban air quality: A preliminary study of four major southeastern cities

The Southeast Regional Assessment has been conducted as part of the US Global Change Research Program's National Assessment of the potential consequences of climate variability and change. However, not as much attention has been given to air pollution concerns in this National Assessment or in other climate change studies as to the impacts in agriculture or water resources management even though air pollution levels, especially the concentration of ground-level ozone are dependent on meteorological conditions. For example, decreases in wind speed and mixing heights and increases in air temperatures in an urban area associated with climate change may increase air pollution levels masking or reversing the effects of emission reductions. These changes can then cause a violation of ambient air standards triggering substantial control costs, which can easily exceed several hundred million dollars for a medium size urban area. Because analytical tools and data needed to fully examine the air quality and climate relationships are lacking at the present, a preliminary assessment using a statistical regression model was conducted to examine the potential effects of climate change on maximum ozone concentrations in the southeastern U.S. Ozone is perhaps the most significant air pollution problem in this region. Sunlight coupled with a large biogenic source of volatile organic compounds has made the Southeast vulnerable to increasing levels as population has increased. Many areas in the Southeast marginally meet ozone air quality standards. Any increase in ozone levels would substantially increase the number of cities and urban areas having to adopt costly control measures. The regression model considers the relationships among temperature, precipitation, relative humidity, vapor pressure, solar radiation, and measured ozone concentrations for extreme days. Using these relationships, this model was coupled to climate scenarios for 2030 and 2099 to estimate changes in maximum ozone concentrations for four southeastern cities: Atlanta, Birmingham, Memphis, and Nashville. These estimated changes were then compared to 1995 base values, which represented measured ozone concentrations from selected sites within each urban area. In this paper, maximum daily ozone concentrations for the four cities will be presented for 1995, 2030, and 2090 based on changes in future climate predicted by the Hadley model scenario. In addition, results will be given for a series of sensitivity studies where these climate factors (i.e., temperature, precipitation, and solar radiation) are varied in a range broader than those forecasted by the climate model. The study results will show which urban areas might cross into a non-attainment designation as a result of future climate variations.