HOW DID THE STUDY ESTIMATE CONCENTRATIONS OF AIR TOXICS ?
The study predicts 1990 pollutant concentrations by combining estimates of pollutant emissions from a variety of sources (cars, factories, waste combustors, dry cleaners, etc.) with a computer model that simulates the behavior of pollutants after being emitted. The computer model considers factors such as wind speed and direction, breakdown of pollutants, and removal of pollutants in rainfall, to estimate the concentrations of pollutants in outdoor air resulting from the estimated emissions. The authors of the study compared the modeled air toxics concentrations to the limited available monitoring data. This comparison showed that the study’s modeled concentrations of air toxics have a general tendency to underestimate concentrations (underestimates were found about three times as frequently as overestimates). The study’s modeling methodology was peer-reviewed by the EPA’s Science Advisory Board in 1996. This board is a body of outside scientific and technical experts who review techni
