An accounting or measurement of specified toxic levels of pollutants in the air. Based on the EPA air quality act, it gives the indicator (number) of different gas phase concentration levels to determine if it is hazardous to be outside or not, that is to breathe the air is a specific region. [School Library Journal; v53; 24; 2007.] [Journal of Environmental Management; v80; 230-236; 2006.] [Resource and Energy Economics; v28; 215-228; 2006.]
