The Impact of the Chesapeake Bay Climate and Boundary Layer Dynamics on Air Pollutant Concentrations during Smog Episodes

A comprehensive set of atmospheric trace gas observations is available for July 2011 in the Baltimore-Washington metropolitan region as part of NASA's DISCOVER-AQ air quality campaign. In conjunction, a NOAA research vessel observed O₃, NO and NO_y during a 10-day experiment over the Chesapeake Bay. Ozone observations over the bay during the afternoon are often 10% - 20% higher than the closest upwind ground sites. Higher ozone over the Chesapeake Bay is of public health concern due to the bay acting as a central hub for leisure activities during the summer. The pattern of higher ozone persists during good and poor air quality days. Furthermore, results from aircraft flyovers often show a large plume of ozone and its precursors 500-1500 meters above the surface of the bay. We suggest that a combination of complex boundary layer dynamics, deposition rates, and unaccounted marine emissions are playing an integral role in the regional maximum of ozone over the Chesapeake Bay. Air quality models are able to predict the regional maximum of ozone over the Chesapeake Bay, but the predictions are often 10-20% higher than observations. Measurements of boundary layer height during the campaign show that WRF, which is used to initialize the air quality models, under predicts boundary layer height over the Chesapeake Bay. This is likely the primary factor for the overestimation of trace gases close to the surface.