Air Quality in Windsor (Canada) and Impact of Regional Scale Transport.

Air Quality Health Index (AQHI) is a scale designed in Canada to help residences understand the impact of air quality on health. This study investigated temporal variability of daily AQHI and impact of regional transport on AQHI in Windsor, Ontario, Canada from 2016 to 2019. The four-year average daily AQHI was 2.9, slightly below the upper limit of the low health risk level of 3. AQHI value decreased from 2.95 to 2.81 during the study period, indicating the improvement of air quality. Half of the days, AQHI were 3 regardless of season. AQHI was higher in the warm season (3.1) than in the cold season (2.6) due to more frequent moderate risk days (27%, AQHI = 4) in warm season and more frequent low risk days (42%, AQHI = 2) in the cold season. Among the three pollutants considered, O₃ was the most frequently reported dominant contributor to daily AQHI (88% of days), followed by NO₂ (12%), especially in the cold season, with small contribution from PM_2.5 (<1%). Trajectory analysis found that AQHI ≤ 3 days were closely associated with air masses from the north and northwest, whereas AQHI > 3 days were closely associated with air masses from the west and southwest. This is because northerly flows brought in clear air mass owing to less industrial facilities. Polluted air masses were transported from the south of Windsor, where several industrial states of the US were located. Directional AQHI resembles O₃ more than NO₂ or PM_2.5 concentrations do. Further improvement of AQHI in Windsor could be challenging because O₃ concentrations have continued to increase in recent years. Thus, more effective control measures to mitigate O₃ pollution are warranted to reduce its impact on human health and the environment. [ABSTRACT FROM AUTHOR]