A Characterization of Interregional Transport of Ozone and Precursors into an Urban Area

Abstract

Evidence of the interregional transport of ozone and its precursors has been documented by many investigators. Monitoring air pollution upwind of urban areas in order to characterize the ozone and precursor transport into the city is not common, however, and understanding this phenomenon is essential to properly design control strategies to attain and maintain the ozone ambient air quality standard, and to develop models for assessing the impact of interregional transport of ozone and precursors.

To address the issue of transport, a study was performed during the summer of 1978 in the vicinity of Philadelphia, Pennsylvania. Data was collected at special surface transport sites upwind and downwind of Philadelphia at already existing surface monitoring sites. Data was also collected by an instrumented helicopter. No obvious transport of significant concentrations of ozone and precursors was observed along the surface into Philadelphia during the early morning hours; neither was transport of significant precursor concentrations aloft apparent; transport of ozone aloft, in excess of 0.08 ppm, was observed, however. There is no significant spatial variation in ozone concentrations in the air mass aloft along the upwind boundary of Philadelphia. On days where strong transport into the city was observed, the incoming mass generally approaches Philadelphia from the west in a broad, anticyclonicaily-curved path and does not routinely traverse any particular urban area upwind.