The threat of air pollution is not new, but it is changing. Air pollution has contributed to death and disease and has hurt economic prospects and community resilience for decades. During that time, policies and technologies have drastically improved air quality in some areas, saving lives, and proving that pollution is not an inevitable by-product of economic development.
Air pollution is a complex mixture of particles and gases with sources and composition varying over space and time. While hundreds of chemical compounds can be measured in the air, governments typically measure only a small subset as indicators of the different types of air pollution and major sources contributing to that pollution.