The role of transboundary flow on 1995 ozone levels in Ontario, Canada
- Ontario Ministry of Environmental and Energy, Etobicoke, Ontario (Canada)
Exceedances of the ozone criterion in Ontario are often widespread and associated with episodes. Here an episode refers to distinct meteorological events in which there is the simultaneous occurrence of widespread (hundreds of kilometers) elevated ozone levels (greater than 80 ppb maximum hourly concentration). An examination of the ozone data for 1995 (based on 45 monitoring sites) indicates that there were 16 such episode days in Ontario. This was slightly higher than the numbers reported in 1992 to 1994. The trend in the number of ozone episode days in Ontario over the past 17 years show the highest frequencies in 1988, 1991 and 1983. Associated air parcel back trajectories on the 16 episode days all show transboundary flows from the neighboring states of the U.S. Typically air parcels traversed regions south-southwest of southwestern Ontario. In 1995 there were, however, a number of episode days with associated southeasterly flows compared to that experienced in previous years. For example, there were about 25 such cases in 1995 compared to 8% in 1991 and none in 1988. On ozone excursion days (exceedances of 124 ppb) in Michigan, transboundary flows were significant and ozone levels in Ontario were generally high. These results support the concept of a common airshed between Ontario and neighboring states and that southern Ontario is located often within the northern edge of the ozone problem area in eastern North America.
- OSTI ID:
- 351020
- Report Number(s):
- CONF-970677--
- Country of Publication:
- United States
- Language:
- English
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