Effects of Weather Fronts on Ozone Transport

Abstract

The object of the research discussed in this paper has been to define special meteorological conditions that are conducive to the long-range transport of ozone and its precursors, especially in highly urbanized areas like the northeastern United States. Long-range transport is an important factor in the design of ozone control strategies. Routinely collected air quality data, special data from the Northeast Oxidant Study, and National Weather Service data and analyses were combined to determine relationships among source areas, areas of high ozone concentration, and air movement associated with different weather systems. In the eastern United States, the warm, southwesterly winds preceding weather fronts were found to provide favorable conditions for ozone formation and transport. The alignment of the coastal source areas is such that particularly dramatic buildups of ozone result, followed by abrupt decreases in concentration as colder, cleaner air behind a front replaces the polluted air ahead of it. Examples of several such events have been analyzed. Although air movement associated with frontal passages is only one of the important situations causing long-range transport and ozone buildup in the Northeast, the events are sufficiently common that they must be considered in the design of control strategies. Furthermore, the fact that ozone buildups are found in conjunction with frontal passages belies the common assumption that stagnating high pressure systems are required for important violations of ozone standards in the eastern United States. The results show that extended source areas, when aligned with the air flow, may lead to significant ozone concentrations even in the decidedly unstagnant air ahead of frontal zones.