Effects of light duty gasoline vehicle emission standards in the United States on ozone and particulate matter

More stringent motor vehicle emission standards are being considered in the United States to attain national air quality standards for ozone and PM2.5. We modeled past, present and potential future US emission standards for on-road gasoline-fueled light duty vehicles (including both cars and light trucks) (LDVs) to assess incremental air quality benefits in the eastern US in 2022. The modeling results show that large benefits in ozone and PM2.5 (up to 16 ppb (14%) reductions in daily maximum 8-h ozone, up to 10 ppb (11%) reductions in the monthly mean of daily maximum 8-h ozone, up to 4.5 m gm � 3 (9%) reductions in maximum 24-h PM2.5 and up to 2.1 m gm � 3 (10%) reductions in the monthly mean PM2.5) accrued from the transition from Tier 1 to Tier 2 standards. However, the implementation of additional nationwide LDV controls similar to draft proposed California LEV III regulations would result in very small additional improvements in air quality by 2022 (up to 0.3 ppb (0.3%) reductions in daily maximum 8-h ozone, up to 0.2 ppb (0.2%) reductions in the monthly mean of daily maximum 8-h ozone, up to 0.1 m gm � 3 (0.5%) reductions in maximum 24-h PM 2.5 and up to 0.1 m gm � 3 (0.5%) reductions in the