Surface measurements of windspeed, direction, and ozone concentration collected at Walloops Island, Virginia, during the summers of 1977 and 1978 are analyzed to study the effects of the dominant mesoscale sea breeze circulation on th local photochemical oxidant levels. A bimodality in the atmospheric dynamics is linked to systematic variations in ozone concentration. It is concluded that during certain phases of the two circulation modes, increased wind speed reduces the resistance of the earth's surface to the deposition of ozone, and decreased ozone concentration levels result. For other phases, light wind occur, signifying high resistance to deposition and high ozone levels. This modulation by the local dynamics is a major impediment for pollutant studies in coastal environments, especially those centering on transport, because it tends to mask other processes that may be occurring.