Short-lived climate pollutants (SLCP) contribute as much as 40% to anthropogenic radiative forcing. Bart Croes will collaborate with Steve Montzka to apply California’s SLCP emission inventory methods from 2005 to 2030 for the other 49 States, and identify control paths to meet California’s targets – 40% below 2013 levels by 2030 for hydrofluorocarbons and methane emissions, and 50% below for anthropogenic black carbon. Since the 1970 Clean Air Act, the U.S. improved air quality while the economy grew and vehicle miles traveled increased. Nevertheless, unhealthy PM2.5 and ozone exposures are estimated to cause about 90,000 premature deaths each year, and recent data show a general leveling off of progress since 2013-2015. While several publications have identified climate, global background, and emission control factors as likely contributors, a collaboration with Joost de Gouw will synthesize more recent emission models with satellite data to explore additional hypotheses, and apply environmental justice screening techniques demonstrated in California to national air quality trends.