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

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.