Trans-boundary air pollution in Windsor, Ontario (Canada)

Windsor (Ontario) is located on the Canada-US border. Some believe that the heavy industrial facilities such as power generation and automobile production in the neighbouring regions of US greatly affect Windsor's air quality. This study investigates the frequency of air mass exchange between Windsor and the neighbouring US states. Two-day (48-hr) and one-day (24-hr) back trajectories were run using the Hybrid Single-Particle Langrangian Integrated Trajectory (HYSPLIT) model. Windsor Airport (42.27o N, 82.96o W) was the starting point. The model resolution was three days a week. Two calendar years, 2008 and 2009, were modeled thus seasonal and inter-annual variations could be observed. It was found that the fraction of air mass parallel to the border is small. When considering the 48-hr trajectories on an annual basis, 53-55% of air masses arriving Windsor were from the US, whereas the 24-hr trajectories showed a much higher percentage (81-82%). The inter-annual variability between 2008 and 2009 was small. In both years, winter had higher frequency of US to Canada transport than Canada to US. In the other three seasons (spring, summer and fall), one year had more frequent US to Canada transport while the other year had less. It was concluded that overall the US-Canada transport had a higher frequency. However, this alone is inadequate to support the claim of air masses coming from US greatly affect Windsor air quality. Further analyses using state and province wide emission densities and ambient concentrations were conducted for a two-week period during each year to quantitatively assess the trans-boundary movement of air pollutants. Statistical analyses showed no consistent, significant correlations between the travel path of the air mass prior to arrival and the measured NO2 or PM2.5 concentrations at the receptor.