![]() ![]() 2012), with some of them leading to elevated O 3 and violations of the EPA 8-h O 3 mixing ratio standard of 75 ppbv. During the Chemistry of the Atmospheric Boundary Layer Experiment (CAPABLE ) project in July 2010 in Hampton, Virginia (37.07º, −76.36º) near the mouth of the Chesapeake Bay, several instances of bay breezes were observed (Martins et al. Participation in two recent projects examined these effects and provided the motivation for a long-term historical analysis of bay breezes and O 3. In addition to the reduced deposition of O 3, minimal nighttime titration of O 3 from a lack of NO over the water surface will decrease O 3 loss, leading frequently to higher O 3 observations over a water body at night (Mao et al. Because of this, high near-surface O 3 mixing ratios may accumulate over the water in the morning when the land/bay breeze circulation is dominant. This weaker deposition velocity produces less of a flux of O 3 onto the water surface where it is effectively removed from the system. Ozone readily deposits to surfaces and vegetation over land, but its deposition velocity over water (~0.07 cm s −1) is five to six times slower than over a terrestrial (~0.4 cm s −1) surface (Lenschow et al. While air masses originating from marine environments generally contain low O 3, the land/bay breeze system transports morning terrestrial emissions and O 3 over the water surface that then recirculate back to coastal locations (Banta et al. In addition to similar meteorology controlling both O 3 production and bay breeze initiation, the behavior of O 3 over water surfaces is quite different than over land. Previous studies have found the bay breeze to be a mechanism through which emissions and O 3 from urban areas can be transported to more rural locations (Angevine et al., 2004 Darby et al. The bay breeze front can then transport O 3-rich air masses and pollution well inland (Darby 2005 Lin et al. The stagnant conditions necessary to allow a bay breeze to become the dominant circulation during the daytime also allows a buildup of O 3 in the boundary layer due to lack of venting and the accumulation of pollutants (Rappenglück et al. 1999), concentrating O 3 in a smaller volume (Banta et al. The cooler water and adjacent air temperatures over water also result in lower boundary layer heights relative to farther inland areas (Berman et al. The heat and incoming solar radiation, in the presence of high mixing ratios of NO x and VOCs, can produce high amounts of O 3 over land. The combination of warm weather and intense sunlight needed to cause a temperature gradient from land to water can eventually lead to a bay breeze at coastal locations. The meteorological conditions needed to form a bay breeze and produce O 3 go hand in hand. ( 2012) that highly localized meteorology increasingly drives air quality events at Hampton. ![]() These results suggest that bay breeze circulations are becoming more important to causing exceedance events at particular sites in the region, and support the hypothesis of Martins et al. In conjunction with an overall lowering of baseline O 3 after the 1995-2002 period, the percentage of total exceedances of the Environmental Protection Agency (EPA) 75 ppbv 8-h O 3 standard that occurred on bay breeze days increased at Hampton for 2003–2010, while remaining steady at Baltimore. Anomalies from mean surface O 3 were highest in the afternoon at both sites during bay breeze days in the 2003–2010 study period. Mean eight hour (8-h) averaged surface O 3 values during bay breeze events were 3 to 5 parts per billion by volume (ppbv) higher at Hampton and Baltimore than on non-bay breeze days in all year periods. Each day in the 25-year record was marked either as a bay breeze day, a non-bay breeze day, or a rainy/cloudy day based on the meteorological data. The years were split into three groups to account for increasingly stringent environmental regulations that reduced regional emissions of nitrogen oxides (NO x): 1986–1994, 1995–2002, and 2003–2010. Analyses were performed for the months of May through September for the years 1986 to 2010. Hourly surface meteorological measurements were coupled with surface ozone (O 3) mixing ratio measurements at Hampton, Virginia and Baltimore, Maryland, two sites along the Chesapeake Bay in the Mid-Atlantic United States, to examine the behavior of surface O 3 during bay breeze events and quantify the impact of the bay breeze on local O 3 pollution. ![]()
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