Accountability Assessment of Source-Specific Impacts of Regulations on Emissions and Air Quality Using Positive...

Emission controls targeting electric generating units (EGUs) and mobile sources have been implemented for decades to mitigate PM_2.5 concentrations. Impacts of emission controls on source-apportioned PM_2.5 concentrations (diesel/gasoline vehicles, biomass burning, secondary nitrate, secondary sulfate, soil/road dust, and residual oil estimated via positive matrix factorization) across three U.S. highly urbanized regions─Atlanta, New York City, and the South Coast Air Basin (SoCAB)─from 2005 to 2019 were evaluated. We considered major controls on EGUs, mobile sources, ports, and heating fuel. Daily counterfactual source-apportioned PM_2.5 concentrations without emission controls were estimated based on meteorological indicators and counterfactual emissions using the generalized additive model. Results indicate that emission controls reduced the PM_2.5 concentrations by 65-85% across all regions. Secondary sulfate concentrations without EGU controls would be 4.8 times higher, and diesel-vehicle-related PM_2.5 would increase 6.8 times without mobile controls in Atlanta. Secondary inorganic aerosols in New York City would increase 5-fold from 1.92 to 10.5 μg/m³, shifting the dominant PM_2.5 contributors. Seasonal trends in the counterfactual PM_2.5 concentrations were similar to the actual trends, but the peaks in the counterfactual scenario were clearer than those with emission controls.