This paper presents results from energy, meteorological, and photochemical (air quality) modeling for the Los Angeles Basin, one of the largest and smoggiest urban regions in the U.S. and the world. Our simulations suggest that by mitigating urban heat islands, savings of 5 to 10% in peak utility had may be possible. In addition, heat island mitigation can reduce smog formation by 10-20% in summer, which is as effective as controlling emissions from all mobile sources in the region. For a typical late-August episode, our simulations suggest that implementing cool cities in the Los Angeles Basin would have a net effect of reducing ozone concentrations. Peak concentrations at 3pm decrease by up to 7% (from 220 down to 205ppb) while the total ozone mass in the mixed layer decreases by up to 640 metric tons (a decease of 4.7%). Largest reductions in concentrations at 3pm are on the order of 50ppb whereas the largest increases are on the order of 20ppb. With respect to the National Ambient Air Quality Standard, domain-wide population-weighted exceedance exposure to ozone decreases by up to 20% during peak afternoon hours and by up to 10% during the daytime.