This study investigated impacts of regional transport and meteorology on ground-level ozone (O
3) in the smog season (April–September) during 1996–2015 in Windsor, Ontario, Canada. Data from five upwind stations in the US, which are within 310 km (i.e., Allen Park and
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This study investigated impacts of regional transport and meteorology on ground-level ozone (O
3) in the smog season (April–September) during 1996–2015 in Windsor, Ontario, Canada. Data from five upwind stations in the US, which are within 310 km (i.e., Allen Park and Lansing in Michigan, Erie, National Trail School, and Delaware in Ohio), were included to assess the regional characteristics of O
3. The five US stations showed high degrees of similarity with O
3 concentrations in Windsor, with overall strong correlations (r = 0.567–0.876 for hourly O
3 and r = 0.587–0.92 for 8 h max O
3 concentrations) and a low degree of divergence, indicating that O
3 pollution in the study area shares regional characteristics. Meteorological conditions played important roles in O
3 levels in Windsor. High O
3 concentrations were associated with southerly and southwesterly air mass from which polluted and hot air mass was transported and that enhanced local photochemical O
3 production. In contrast, northerly flows brought in clean, cool, and dry air mass, and led to low O
3 concentrations. Strong correlations were found between numbers of days with 8 h max O
3 concentrations greater than 70 ppb and numbers of days with daily max temperature greater than 30 °C, as well as between daily max temperatures and 8 h max O
3 concentrations. Nearly half (45%) of the high O
3 days (≥90th percentile) occurred in dry tropical weather during 1996–2015, and the 90th percentile 8 h max O
3 was associated with dry tropical weather. Occurrences of both southerly flow hours and dry tropical weather type in the smog season increased during the study period. If there were more hot and dry days in the next few decades due to climate change, the effect of emission control on reducing peak O
3 values would be diminished. Therefore, continued regional and international efforts are essential to control precursors’ emissions and to mitigate O
3 pollution in Windsor.
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