An elevated reservoir of air pollutants over the Mid-Atlantic States during the 2011 DISCOVER-AQ campaign: Airborne measurements and numerical simulations

During a classic heat wave with record high temperatures and poor air quality from July 18 to 23, 2011, an elevated reservoir of air pollutants was observed over and downwind of Baltimore, MD, with relatively clean conditions near the surface. Aircraft and ozonesonde measurements detected w120 ppbv ozone at 800 m altitude, but w80 ppbv ozone near the surface. High concentrations of other pollutants were also observed around the ozone peak: w300 ppbv CO at 1200 m, w2 ppbv NO2 at 800 m, w5 ppbv SO2 at 600 m, and strong aerosol optical scattering (2 � 10 � 4 m � 1 ) at 600 m. These results suggest that the elevated reservoir is a mixture of automobile exhaust (high concentrations of O3, CO, and NO2 )a nd power plant emissions (high SO2 and aerosols). Back trajectory calculations show a local stagnation event