Impact of Bay-Breeze Circulations on Surface Air Quality and Boundary Layer Export

Meteorological and air-quality model simulations are analyzed alongside observations to investigate the role of the Chesapeake Bay breeze on surface air quality, pollutant transport, and boundary layer venting. A case study was conducted to understand why a particular day was the only one during an 11-day ship-based field campaign on which surface ozone was not elevatedin concentrationover the ChesapeakeBay relative to theclosestupwindsiteandwhyhigh ozoneconcentrations wereobservedaloftbyinsitu aircraftobservations. Results show that southerly winds during the overnight and early-morning hours prevented the advection of air pollutants from the Washington, D.C., and Baltimore, Maryland, metropolitan areas over the surface waters of the bay. A strong and prolonged bay breeze developed during the late morning and early afternoon along the western coastline of the bay. The strength and duration of the bay breeze allowed pollutants to converge, resulting in high concentrations locally near the bay-breeze front within the Baltimore metropolitan area, where they were then lofted to the top of the planetary boundary layer (PBL). Near the top of the PBL, these pollutants were horizontally advected to a region with lower PBL heights, resulting in pollution transportoutoftheboundarylayerandintothefreetroposphere. Thiselevatedlayerofairpollutionaloftwas transported downwind into New England by early the following morning where it likely mixed down to the surface, affecting air quality as the boundary layer grew.