An ozone episode in the Philadelphia metropolitan area. Kleinman, L., I., Ryan, W., F., Daum, P., H., Springston, S., R., Lee, Y., N., Nunnermacker, L., J., & Weinstein-Lloyd, J. Journal of Geophysical Research-Atmospheres, 109(D20):-, 2004.
An ozone episode in the Philadelphia metropolitan area [link]Website  abstract   bibtex   
[1] 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-3 and particulate matter less than or equal to 2.5 mum in aerodynamic diameter. We report emission estimates, weather information, surface O-3 monitoring data, and aircraft observations, with a focus on 31 July, the last day of an O-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-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-3 episodes in the northeast, transport on 31 July was limited, and O-3 hot spots occurred close to NOx and volatile organic compound (VOC) emission sources. High O-3 was observed downwind of Baltimore and Philadelphia, both major urban areas. High O-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-3 monitoring data and morning aircraft observations show that the residual layer aloft contained 80 - 100 ppb of O-3 but almost no O-3 precursors. Same-day photochemistry on 31 July caused surface O-3 concentrations to increase by 60 - 80 ppb. Photochemical model calculations indicate O-3 production rates in excess of 20 ppb h(-1) in regions with NOx > 5 ppb. High NOx concentrations are a consequence of poor ventilation. Peroxide observations and calculations indicate that O-3 production is VOC limited in the high-NOx portions of the Philadelphia urban plume. Our results are contrasted against a severe O-3 episode that occurred in 1995. While the 1999 episode had stagnation conditions leading to local O-3 hot spots, there were mesoscale meteorological features in 1995 that favored interregional transport.
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 title = {An ozone episode in the Philadelphia metropolitan area},
 type = {article},
 year = {2004},
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 keywords = {chemistry,hydrocarbons,nashville,northeastern united-states,o-3 formation,ozone,ozone episode,photochemistry,southern oxidants,stagnation episode,tennessee,transport,urban},
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 volume = {109},
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 abstract = {[1] 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-3 and particulate matter less than or equal to 2.5 mum in aerodynamic diameter. We report emission estimates, weather information, surface O-3 monitoring data, and aircraft observations, with a focus on 31 July, the last day of an O-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-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-3 episodes in the northeast, transport on 31 July was limited, and O-3 hot spots occurred close to NOx and volatile organic compound (VOC) emission sources. High O-3 was observed downwind of Baltimore and Philadelphia, both major urban areas. High O-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-3 monitoring data and morning aircraft observations show that the residual layer aloft contained 80 - 100 ppb of O-3 but almost no O-3 precursors. Same-day photochemistry on 31 July caused surface O-3 concentrations to increase by 60 - 80 ppb. Photochemical model calculations indicate O-3 production rates in excess of 20 ppb h(-1) in regions with NOx > 5 ppb. High NOx concentrations are a consequence of poor ventilation. Peroxide observations and calculations indicate that O-3 production is VOC limited in the high-NOx portions of the Philadelphia urban plume. Our results are contrasted against a severe O-3 episode that occurred in 1995. While the 1999 episode had stagnation conditions leading to local O-3 hot spots, there were mesoscale meteorological features in 1995 that favored interregional transport.},
 bibtype = {article},
 author = {Kleinman, L I and Ryan, W F and Daum, P H and Springston, S R and Lee, Y N and Nunnermacker, L J and Weinstein-Lloyd, J},
 journal = {Journal of Geophysical Research-Atmospheres},
 number = {D20}
}
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