Today we review the changes that emission controls implemented in the state of Maryland with the Healthy Air Act in 2009, had on the concentration of SO2 and PM2.5 using measurements from satellites in space as well as ground measurements over the last 10 years. Results indicate that emissions from (coal burning) power plants were reduced by 90% while concentrations of SO2 were reduced by 50% and PM2.5 by 25%- with all of the decline of PM2.5 due to a reduction in sulphur. Results were striking in the decrease of the seasonal peak of SO2 in mid summer when there is a higher power demand. The difference between the greater SO2 emission reduction and concentration reductions shows the added input to the pollution from other than power plants (such as diesel vehicle emissions).
Key Quotes:
“SO2 has been linked to respiratory ailments ..Its residence time, also called atmospheric lifetime, in the lower atmosphere ranges from ∼2 days in the winter to less than 1 day in the summer .. anthropogenic SO2 emissions come mainly from power plants and other coal combustion facilities and have decreased by ∼6%/yr in the last decade…. Sulfate aerosols from SO2 usually peak in summer …and historically account for 50%–60% of the ground-level PM2.5 observed in the eastern United States “
“PM2.5,the main source of air pollution mortality in the United States..is mainly removed in precipitation processes and has an atmospheric lifetime of about 10 d. PM2.5 is also responsible for haze, which usually dictates the limit of visual range .. impacts the hydrological cycle ..and affects the weather and climate” “Peak PM2.5 concentrations are observed in the summer, when the rate of oxidation of gaseous precursors, SO2, and volatile organic compounds (VOC) to particulate matter peaks.”
“Essentially, all of the improvement in PM2.5 can be attributed to the decline in sulfate. The decrease (1.7 μgm−3, 42% out of 4.1 μgm−3) in sulfate is smaller than that for total PM2.5 (2.5 μgm−3, 20% out of 12.7 μgm−3), but most of the sulfate in the eastern United States is neutralized, and when corrected for the greater molecular weight of (NH4)2SO4 (132 g/mole) compared to SO4 2– (96 g/mole), the resulting change is −2.4 μgm−3 and can account for most (93%) of the observed drop in PM2.5.”
“The Healthy Air Act, implemented in Maryland in 2009–2010, provided an exceptional opportunity to test the impact of a step change in local emissions on ambient pollution levels. This Maryland regulation reduced in-state power plant emissions of SO2 by ∼90%; long-term aircraft measurements, surface observations, and satellite products showed a reduction in column SO2 of ∼50%, while PM2.5 and AOD showed a reduction of ∼25%.”
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