1. Variability in surface ozone background over the United States: Implications for air quality policy Fiore, Arlene M.; Jacob, Daniel J.; Liu, Hongyu; Yantosca, R. M.; Fairlie, T. D.; Li, Q. 2003 Articles Tropospheric chemistryAir quality--StandardsOzoneMeteorologyClimatic changesAtmospheric chemistryUnited States. Environmental Protection Agency