Tropospheric Ozone in Louisiana and Synoptic Circulation


Robert Rohli

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Abstract Tropospheric ozone (O3) is a pollutant of increasing concern in many urban areas in the United States. There is an increasing need to understand the geographical and meteorological properties associated with O3, particularly because of the changing criteria that are being implemented by the U.S. Environmental Protection Agency to monitor O3. This research examines the relationship between O3 mixing ratios in Louisiana and surface and low-tropospheric synoptic circulation patterns. Results suggest that local conditions and synoptic influences are both important in determining the behavior of observed O3 in Louisiana during this period in which “exceedance” frequencies decreased until 2000–01, at which time they increased again. Furthermore, the expected pattern of surface anticyclonic activity, low-tropospheric ridging, weak pressure gradients, and subsidence from the lower troposphere is found to be associated with anomalously high O3, both at most local sites in the state and on days with anomalously high O3 statewide. More surprising, however, is the tendency for high O3 to be associated with low surface pressure in the Great Plains, perhaps in advance of a midlatitude wave cyclone to the north. This and other surface patterns may be linked to advection from the southeastern Texas urban–industrial corridor. A temporally increasing tendency for surface and lower-tropospheric ridging over the 1994–2001 study period provides at least a partial explanation for the absence of a frequency decline in statewide anomalously high ozone days during a time of increasing public awareness and concern for meeting the O3 standard.

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Journal of Applied Meteorology

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