We examined the impact of large US emissions changes, similar to those estimated to have occurred between 2005 and 2012 (high and low emissions cases, respectively), on inorganic PM_2.5 sensitivities to further NO_x, SO₂, and NH₃ emissions reductions using the chemical transport model GEOS-Chem. Sensitivities to SO₂ emissions are larger year-round and across the US in the low emissions case than the high emissions case due to more aqueous-phase SO₂ oxidation. Sensitivities to winter NO_x emissions are larger in the low emissions case, more than 2x those of the high emissions case in parts of the northern Midwest. Sensitivities to NH₃ emissions are smaller (∼40%) in the low emissions case, year-round, and across the US. Differences in NO_x and NH₃ sensitivities indicate an altered atmospheric acidity. Larger sensitivities to SO₂ and NO_x in the low emissions case imply that reducing these emissions may improve air quality more now than they would have in 2005; conversely, NH₃ reductions may not improve air quality as much as previously assumed.

© 2015 American Chemical Society