Atrazine is one of the most widely used herbicides in North America and has been primarily applied to corn production in the Great Lakes basin for over 30 years. During 1996-2002, atrazine concentrations in the atmospheric gas and particle phases were investigated at three Canadian Integrated Atmospheric Deposition Network (IADN) sites including two lakeside sites (Burnt Island and Point Petre) and a rural inland site (Egbert). Strong seasonality with peak concentrations occurring in late April-early July was observed. An atrazine usage map for Canada (sum: 870 t) and the United States (sum: 34 500 t) in 2002 was created. Local application and regional atmospheric transport both appear to contribute to its atmospheric occurrence, while the latter might episodically result in high concentrations events. No strong temperature dependence was observed for atrazine particle-gas partitioning. Recent measurement results of atrazine in precipitation samples collected at Egbert and another agricultural site, Vineland, through the Canadian Atmospheric Network for Currently Used Pesticides (CANCUP), are also presented, Dry, wet, and gas exchange deposition all contribute to atmospheric inputs of atrazine to the Great Lakes. For Lake Ontario, gas exchange is estimated to be of similar magnitude to dry and wet deposition.