Spatial-temporal variations in snowfall chemistry in the montreal region

Snowfall was collected on an event basis for 6 winter storms in 1980 at 10 locations around the greater Montreal region. Six sites were urban, 2 suburban and 2 rural (small town). For all storms, 4 of the urban stations had the highest pH of the 10 locations, with the 6 Montreal Island sites having the highest chemical concentrations. Employing principal component analysis, two chemical species associations are apparent: (1) an alkaline/fly ash factor and (2) an ‘acid snow’ factor. The former indicates the possible effects of local emissions. Generally, the storms produced individual chemical concentrations patterns enabling five of the storms to be separated into distinct events. Three storms were designated as ‘type’ storms in which pH, sulphates, and nitrates varied according to individual storm characteristics and air trajectories. If the air trajectory passed over SO_x and NO_x sources to the west and south-west (Ontario-Great Lakes region) pH values were lower and sulphate and nitrate concentrations in the snowfall higher.