Two key air pollutants can affect asthma. One is ozone (found in smog). The other is particle pollution (found in haze, smoke, and dust). Studies show that when ozone and particle pollution are in the air, adults and children with asthma, and other lung diseases, are more likely to have symptoms.

Studies also show that air pollution can trigger heart attacks, stroke, and irregular heart rhythms—especially in people who are already at risk for these conditions. Also, for people with a medical condition called heart failure, air pollution can further reduce the ability of the heart to pump blood the way that it should. Particle pollution is the pollutant of greatest concern for triggering these effects.