Ambient Air Quality

Ambient air quality refers to the concentration of gases, particles, or other elements in the outdoor atmosphere—from either natural or anthropogenic sources. The term quality is objective and gives an indication of what the concentration of a constituent of air is in relation to certain thresholds or standards. If a concentration is above the threshold, air quality is considered poor or, in some cases, even hazardous to human health. An applicable geographic area is often termed a “nonattainment” area. In these instances, the air is considered “polluted,” and the elevated constituent is a pollutant. Thresholds for different pollutants are determined with reference to human health. Standards are set by the World Health Organization (WHO), though in some countries thresholds have been modified by national or ...