Lake breezes occur frequently in the Great Lakes region of eastern North America. The region includes several major metropolitan areas with significant sources of pollution. As well, pollution in the nearby Ohio Valley is often transported into the region. We use data collected during the 2001 ELBOW (Effects of Lake Breezes On Weather Project) in southern Ontario, as well as air quality data collected at the same time, to study the effects of lake breezes in pollution events. Lake breeze fronts are identified using integrated analyses of observations obtained from satellite, radar and surface networks. Air quality data were collected from stations run by Environment Canada and by the Ontario Ministry of the Environment. Air quality data were also obtained from research aircraft which flew transects between Lakes Erie and Huron as part of ELBOW. The analysis will include ground level ozone, PM2.5, SO2, NO and NO2.

Most of the identified lake breezes and smog episodes occurred under similar meteorological conditions in summer 2001 in the Great Lakes area. The hourly averaged ozone and PM2.5 concentrations on days with lake breezes are significantly higher than that on days without lake breezes. A significant feature of lake breeze impact is that, at a particular location, the passing of lake breeze front may cause the ozone concentration to increase rapidly by tens of ppb. However, the arrival of lake breeze can also have different impacts at different locations. For example, at one location, lake breeze front resulted in a sharp increase in the NOx concentration and little change in the ozone concentration; and at another location, it brought a small increase in the NOx concentration and a sharp increase in the ozone concentration. It indicates the source of pollutants and the origin of the air mass over the lake are critical to the lake breeze impact on air quality for lakeshore and inland locations. Our discussion will include data analysis and model simulations.