Epidemiologic studies suggest that episodes of asthma are exacerbated by smog events.
However, controlled human exposure studies have not been able to determine the specific pollutants that are responsible for these findings, nor do people with asthma appear to respond more intensely to ozone or nitrogen dioxide than healthy people in laboratory settings. However, some evidence indicates that people with asthma may be more sensitive to acid aerosols than healthy subjects. Current risk estimates for air pollutants are calculated largely on the basis of the effects observed in humans exposed to individual gases in laboratory studies. Little is known about any interactive effects of multiple pollutants, or whether a pollutant can sensitize the airways and exacerbate an individual's response to a subsequent pollutant exposure. HEI sponsored the two studies, summarized here, to examine the effects of exposing healthy subjects and subjects with asthma to combined oxidant and acid pollutants.