This report investigates the air pollution reduction benefits associated with mitigating urban heat islands in three U.S. cities. The effects of these measures in Salt Lake City, Baton Rouge, and Sacramento were evaluated through mesoscale meteorological and air quality modeling. The simulations indicate that for these three U.S. cities, adopting heat island reduction measures can result in various meteorological and air quality changes. The meteorological simulations suggest that each of the three pilot cities benefits from reduced ambient air temperatures.  Decreases typically range from 1 to 2K (1.8 – 3.6ºF) over modified areas.

In Salt Lake City, reductions in ambient air temperatures reach up to 2K (3.6ºF) at 1600 LST. The city achieves reductions in ozone concentrations of up to 3 or 4 ppb, the equivalent of about 3.5% if it were compared to an urban peak of 95 ppb. In Baton Rouge, reductions in ambient air temperatures of 0.75K (1.4ºF) are possible and ozone reductions reach up to 4 or 5 ppb, the equivalent of about 4% if compared to an urban peak of 113 ppb. Finally, Sacramento enjoys reductions of 1.2K (2.2ºF) as a result of heat island mitigation measures. Although these temperature reductions are not as large as those experienced in Salt Lake City, for example, their impacts on ozone are relatively larger, with reductions of up to 10 ppb from peak ozone concentrations (about 7% of the peak of 139 ppb). Sacramento enjoys larger reductions in ozone as a result of its larger geographical area.

The modeling work shows that each of the three regions discussed in this report can benefit from implementing heat island mitigation measures. Clearly, the extent to which urban areas can effectively improve local air quality through heat island mitigation depends on numerous factors. These include meteorology and climate, geography, scale, topography, basin morphology, proximity to water bodies, land-use patterns, precursor emission rates and mix, baseline albedo and vegetative fraction distributions, and potential for modification (increase in albedo and vegetative fraction). Based on our modeling efforts, we found that the larger the modified area, the larger the impacts on meteorology and air quality.