Response of SO₂ and particulate air pollution to local and regional emission controls: A case study in Maryland

This paper addresses the questions of what effect local regulations can have on pollutants with different lifetimes and how surface observations and remotely sensed data can be used to determine the impacts. We investigated the decadal trends of tropospheric sulfur dioxide (SO 2 ) and aerosol pollution over Maryland and its surrounding states, using surface, aircraft, and satellite measurements. Aircraft measurements indicated fewer isolated SO 2 plumes observed in summers, a ∼40% decrease of column SO 2 , and a ∼20% decrease of atmospheric optical depth ( AOD ) over Maryland after the implementation of local regulations on sulfur emissions from power plants (∼90% reduction from 2010). Surface observations of SO 2 and particulate matter ( PM ) concentrations in Maryland show similar trends. OMI SO 2 and MODIS AOD observations were used to investigate the column contents of air pollutants over the eastern U.S.; these indicate decreasing trends in column SO 2 (∼60% decrease) and AOD (∼20% decrease). The decrease of upwind SO 2 emissions also reduced aerosol loadings over the downwind Atlantic Ocean near the coast by ∼20%, while indiscernible changes of the SO 2 column were observed. A step change of SO 2 emissions in Maryland starting in 2009–2010 had an immediate and profound benefit in terms of local surface SO 2 concentrations but a modest impact on aerosol pollution, indicating that short‐lived pollutants are effectively controlled locally, while long‐lived pollutants require regional measures.