Local Recirculations and Implications on Planetary Boundary Layer Dynamics and Air Quality

Cities in coast environments often contain a large and diverse source of emissions (i.e. automobiles, ships, power plants, and petrochemical plants) which combined with complex local scale circulations from nearby water bodies can led to high ozone events. In recent years, studies have shown sea and bay breeze circulations to play an important role in coastal air quality as they can contribute to next-day pollution and create a period of conditions ideal for the buildup of ozone precursors. Air masses previously carried offshore by the nighttime land-breeze, can return onshore during with the onset of the bay-breeze. In these cases, the land/sea breeze recirculation can contribute to increased upwind pollutant concentrations in addition to influencing planetary boundary layer (PBL) dynamics. Additionally, the convergence of an offshore synoptic flow and the sea breeze create a period of stagnation that favor the accumulation of pollutants that can lead to high ozone concentrations. The convergence also created a lofted return flow above the sea/bay breeze. Here, we investigate the effect of the bay breeze circulation on both PBL dynamics and on the vertical and horizontal distribution of pollutants during high ozone events in the coastal regions of Houston, TX and Baltimore, MD. Mixing layer height retrievals from multiple ceilometers placed around the Washington/Baltimore/Chesapeake Bay area are analyzed as these provide continuous monitoring of the mixing layer. Additional wind profiler, sonde, and surface chemical measurements, are analyzed in order to assess the role of local circulations in the redistribution of polluted air masses. Previous studies in similar coastal regions found that the front-like meeting of the sea/bay breeze and synoptic flow could be key in the daytime vertical distribution of pollutants over coastal sites. Moreover, the arrival of the sea/bay breeze was also seen to disrupt the mixing layer as the sea breeze pushes air inland and is replaced by cooler marine air.