Anatomy of Two Ozone Transport Episodes in the Washington, D.C., to Boston, Mass., Corridor

During the summer months of 1975, the Interstate Sanitation Commission, in cooperation with the States of New York, New Jersey, and Connecticut and the Brookhaven National Laboratory, conducted a series of studies to characterize ozone transport in the Washington, D.C., to Boston, Mass., corridor. Periods of ozone concentrations above 120 ppb in the New Jersey-New York-Connecticut area were generally preceded by a surface wind shift from a northwest quadrant to a southwest quadrant. On several occasions prior to the wind shift, significantly lower values of ozone (between 30 and 60 ppb) were observed over the area. Synoptic surface weather maps indicated that the shift to a southwest flow preceding these episodes of increased ozone concentrations frequently corresponded to the onset of the return flow around a high-pressure system. An in-depth analysis of two such occurrences during July and August is presented. The arrival and movement of the high concentrations of ozone are supported by continuous surface ozone monitoring data, aerial ozone measurements obtained during the morning and afternoon, meteorological soundings examining local conditions, and air trajectory analyses demonstrating the mesoscale movement of particular parcels of air.