“…The use of air quality zones (AQZs) as a tool for air management was identified as early as the 1960s (Breivogel et al, 1961;Holland et al, 1960) and was first mandated for State Implementation Plans (SIPs) under the U.S. Clean Air Act (CAA) of 1990 (U.S. Environmental Protection Agency [EPA], 1990). In the United States, AQZs are based on designated air quality control regions (AQCRs) that include defined municipalities and groups of intrastate and interstate counties (40CFR81, 1991).…”