Source apportionment of ozone and fine particulate matter in the United States for 2016 and 2028

The air quality model CAMx is used to conduct source apportionment modeling of both O3 and PM2.5 over the continental United States (CONUS) for 2016 and 2028. The model is configured to track sulfate, nitrate, SOA, and primary PM2.5, including elemental metals, with PSAT and O3 with OSAT. The source apportionment simulations differentiate emissions from 10 regions and 9 sectors separately. Simulated source contributions are scaled using ratios of three-year averages of observations to base year simulation results to reduce modeling biases. Comparative analyses of the 2016 and 2028 source contributions are performed at the CONUS, NOAA climate region, and MSA levels. With reductions of emissions regulated by existing rules, the CONUS wide decrease of O3 from 2016 to 2028 is over 10% while PM2.5 decreases by ∼7.5%. Long-distance cross-boundary transport contributes ∼50% of O3 at regional levels but can reach 70% in some MSAs. Denver, Detroit and Phoenix MSAs receive over 70% non-local source contributions to O3. From 2016 to 2028, the relative portion of ozone due to cross-boundary transport contributions are estimated to increase while the contribution of local sources decreases to ∼30%. In contrast, cross-boundary transport contributes only ∼10% to PM2.5, and this contribution changes very little from 2016 to 2028, while local sources contribute ~60%. “On-road” emissions reductions contribute the most to the concentration decreases from 2016 to 2028 for both O3 and PM2.5, followed by EGU and “non-road” sources. The relative contributions of “other point” and “other area” sources increase from 2016 to 2028. Hence more efforts should be made to control emissions from “other point” and “other area” sources.