The Development and Investigation of Eight Northeast Air Quality Case Studies

Eight case studies were investigated to analyze weather patterns associated with ozone concentrations and air quality. The northeast study area included Maine, New Hampshire, Vermont, New York, Massachusetts, Rhode Island, Connecticut, New Jersey, and Pennsylvania. Events were chosen by examining the 8-hour average ozone concentrations at sites throughout the northeast during the peak ozone season of spring, summer, and fall months from 1999 to 2004. The air quality events were defined by investigating the 8-hour average ozone concentrations and classifying them under specific criteria for good and bad air quality. The cases were chosen by summarizing the weather patterns on the day or days of the event, finding abnormal patterns one would normally not associate with the air quality for that event, and determining if it should be investigated further. The cases include three bad air quality cases, three good air quality cases, and two transition cases. These events include both textbook cases and abnormal cases.

Certain weather patterns can drastically affect this region's air quality. Warm air allows ozone production to increase, while cooler air tends to reduce ozone production. Inversions act as capping features. The lower the inversion, the less volume of air the atmosphere has to mix out the ozone gas. Typically this can lead to higher concentrations of ozone near the surface whereas high-level inversions allow a larger volume of air for the atmosphere to mix out ozone. Leeside troughs forming east of the Appalachians allow for convergence or a pooling effect along the trough axis. Ozone can concentrate along the axis and cause significant localized increases in concentrations. Ozone is a gas that forms through photochemical reactions. Therefore, ozone production is minimal under cloudy conditions. Precipitation is able to wash out the ozone gas and much particulate matter from the air. Onshore flow can also concentrate ozone along a coastal boundary as well as create or strengthen a low-level or marine inversion. Wind acts as the primary transport of ozone. It can carry ozone gas away from a source and distribute it to areas just outside the source region. Transition case weather patterns often include a strong Bermuda High and a low pressure system over St. James Bay in Canada. In most transition cases, a warm front passes over the northeast and a leeside trough forms. Ozone concentrations increase drastically while the leeside trough moves westward and merges with the approaching cold front. The cold front passes through the area and ozone concentrations drop. When forecasting for an air quality event, it is crucial to consider all these factors.