Evaluating the Effects of Emission Reductions on Multiple Pollutants Simultaneously

Modeling studies over the Philadelphia metropolitan area have examined how emission control strategies might affect several types of air pollutants simultaneously. NOx reductions in July are predicted to increase ozone in the urban core and decrease it elsewhere, decrease PM2.5 and formaldehyde, and slightly increase acetaldehyde and 1,3-butadiene. In January, NOx reductions increase ozone, formaldehyde and acetaldehyde everywhere. VOC reductions decrease aldehydes but have little effect on ozone in this domain. A combination of VOC and NOx reductions reflects the cumulative behavior of each of the emission reductions separately, and minimizes disbenefits for both HAPs and ozone. A comparison of these changes in terms of their effect on health shows that differing behavior of PM2.5 and ozone can counterbalance each other to some extent. While changes in HAPs are affected by changes to reduce ozone and PM2.5, their effect on health impacts is smaller than PM2.5 and ozone. This study supports considering effects of multiple pollutants in determining optimum pollution control strategies.