An Integrated Observational Analysis of Ozone Sources and Transport Patterns Downwind of a Coastal Megacity

Nonattainment of the ozone national ambient air quality standard is a persistent issue for multiple shoreline and coastal regions in the Eastern United States. Ozone exceedances in these regions are typically associated with summertime high pressure systems, high temperatures and mesoscale shoreline circulations that act to stratify transported ozone and its precursors in shallow layers over the water surface. We use soundings, remote sensing measurements of NO2, ozone profiles, ceilometer backscatter, and outgoing shortwave radiances, along with conventional meteorological and air quality monitoring systems, over and downwind of New York City, to better characterize the depth of this stratified layer, the interplay of mesoscale fronts as a function of the larger scale synoptic winds, and the relationship of ozone formation rates to a key precursor, nitrogen dioxide (NO2), and ambient temperature. We briefly compare and contrast the patterns of ozone sources and transport downwind of New York City to that downwind Chicago, Milwaukee and other cities along Lake Michigan, to highlight important differences driven by the distinct geographies of these two shoreline regions.