Response of inorganic fine particulate matter to emission changes of sulfur dioxide and ammonia: the eastern United States as a case study. 
A three-dimensional chemical transport model (PMCAMx) was used to investigate changes in fine particle (PM2.5) concentrations in response to changes in sulfur dioxide (SO2) and ammonia (NH3) emissions during July 2001 and January 2002 in the eastern United States.  A uniform 50% reduction in SO2 emissions was predicted to produce an average decrease of PM2.5 concentrations by 26% during July but only 6% during January.  A 50% reduction of NH3 emissions leads to an average 4 and 9% decrease in PM2.5 in July and January, respectively.  During the summer, the highest concentration of sulfate is in South Indiana (12.8 microg x m(-3)), and the 50% reduction of SO2 emissions results in a 5.7 microg x m(-3) (44%) sulfate decrease over this area.  During winter, the SO2 emissions reduction results in a 1.5 microg x m(-3) (29%) decrease of the peak sulfate levels (5.2 microg x m(-3)) over Southeast Georgia.  The maximum nitrate and ammonium concentrations are predicted to be over the Midwest (1.9 (-3)g x m(-3) in Ohio and 5.3 microg x m(-3) in South Indiana, respectively) in the summer whereas in the winter these concentrations are higher over the Northeast (3 microg x m(-3) of nitrate in Connecticut and 2.7 microg x m(-3) of ammonium in New York).  The 50% NH3 emissions reduction is more effective for controlling nitrate, compared with SO2 reductions, producing a 1.1 microg x m(-3) nitrate decrease over Ohio in July and a 1.2 microg x m(-3) decrease over Connecticut in January.  Ammonium decreases significantly when either SO2 or NH3 emissions are decreased.  However, the SO2 control strategy has better results in July when ammonium decreases, up to 2 microg x m(-3) (37%), are predicted in South Indiana.  The NH3 control strategy has better results in January (ammonium decreases up to 0.4 microg x m(-3) in New York).  The spatial and temporal characteristics of the effectiveness of these emission control strategies during the summer and winter seasons are discussed.