There are 188 hazardous air pollutants (HAPs), including chemicals that are associated with cancer, neurological, respiratory, reproductive and developmental effects and other adverse effects on human health. Very little monitoring for hazardous air pollutants takes place.
In 1990, the U.S. Congress identified 188 specific pollutants and chemical groups as hazardous air pollutants. Recent studies have detected HAPs at concentrations that warrant public health concern in many cities. There are fewer than 50 monitoring stations measuring outdoor levels of HAPs in the entire U.S.