Methodologies for incorporation of synergistic effects in the calculation of the Pollutant Standards Index

The United States Environmental Protection Agency developed the Pollutant Standards Index (PSI) to provide the public with an overall assessment of daily air quality. PSI values are determined from measured concentrations of five criteria air pollutants: carbon monoxide, nitrogen dioxide, ozone, sulfur dioxide, and particulate matter. However, the PSI calculation is subject to certain inherent limitations. The PSI neglects the role of synergism between the individual pollutants in affecting air quality and human health or property. Two methodologies for synergistic PSI calculation have been evaluated to provide a better understanding of the severity of the damage caused by the pollutants.