An ozone episode in the Philadelphia metropolitan area
In July and August 1999 a Northeast Oxidant and Particle Study field campaign was conducted in the Philadelphia metropolitan area to determine causes for episodically high levels of O{sub 3} and particulate matter {<=}2.5 {micro}m in aerodynamic diameter. We report emission estimates, weather information, surface O{sub 3} monitoring data, and aircraft observations, with a focus on 31 July, the last day of an O{sub 3} episode in which concentrations in Philadelphia reached 165 ppb, the highest level observed there in the past 11 years. As is common in the northeastern states, this O{sub 3} episode started with the development of a broad ridge over the central United States and ended with the northeast corridor under the influence of an Appalachian lee trough with airflow from the SW in an along-corridor direction. For a portion of the morning of 31 July, winds were nearly stagnant, allowing local emissions to accumulate. In contrast to typical O{sub 3} episodes in the northeast, transport on 31 July was limited, and O{sub 3} hot spots occurred close to NO{sub x} and volatile organic compound (VOC) emission sources. High O{sub 3} was observed downwind of Baltimore and Philadelphia, both major urban areas. High O{sub 3} was also observed in a less likely region near the Delaware-Pennsylvania border, downwind of Wilmington, Delaware, but near utility and industrial emission sources. Surface O{sub 3} monitoring data and morning aircraft observations show that the residual layer aloft contained 80-100 ppb of O{sub 3} but almost no O{sub 3} precursors. Same-day photochemistry on 31 July caused surface O{sub 3} concentrations to increase by 60-80 ppb. Photochemical model calculations indicate O{sub 3} production rates in excess of 20 ppb h{sup -1} in regions with NO{sub x} > 5 ppb. High NO{sub x} concentrations are a consequence of poor ventilation. Peroxide observations and calculations indicate that O{sub 3} production is VOC limited in the high-NO{sub x} portions of the Philadelphia urban plume. Our results are contrasted against a severe O{sub 3} episode that occurred in 1995. While the 1999 episode had stagnation conditions leading to local O{sub 3} hot spots, there were mesoscale meteorological features in 1995 that favored interregional transport.
- Research Organization:
- SUNY Research Foundation on behalf of College at Old Westbury
- Sponsoring Organization:
- USDOE - Office of Energy Research (ER)
- DOE Contract Number:
- FG02-98ER62586
- OSTI ID:
- 895146
- Report Number(s):
- DOE/ER/62586-1; Pub3
- Journal Information:
- Journal of Geophysical Research, Vol. 109, Issue D20302
- Country of Publication:
- United States
- Language:
- English
Similar Records
Effect of Regional-Scale Transport on Oxidants in the Vicinity of Philadelphia During the 1999 NE-OPS Field Campaign
A comparative study of O{sub 3} formation in the Houston urban and industrial plumes during the TEXAQS 2000 Study.