Source types in Canadian precipitation chemistry

Abstract

Precipitation data generated by Canadian Air and Precipitation Monitoring Network (CAPMoN) have been analysed by an iterative multiple linear regression method, revealing five source types or components, each with distinctive seasonal and geographic variations. Each source types has its characteristics chemical profile. The profiles suggest that two of the source types are rural (apparently derived from fertilizer and soil), two are urban/industrial (apparently derived from SO2 and NOx emissions), and one is sea salt. The NOx-derived component is highly acidic, the SO2-derived component is also very acidic, the fertilizer component is slightly alkaline, and the soil component is more alkaline. Charge balance calculations show a fairly consistent deficit in anions, a deficit which is especially important for the NOx-derived component. The anion deficit results suggest that more complete chemical analyses are required. The chemical profiles from CAPMoN data have been used to determine the component contributions to precipitation data collected in Manitoba by the provincial Ministry of the Environment. Back trajectories for the Manitoba data show distinct geographic and seasonal effects, including: (i) seasalt input to Manitoba is derived mainly from Hudson Bay and the Arctic, especially in fall and winter; (ii) the SO2 component has ubiquitous sources, including polar sources: (iii) the fertilizer component arrives mainly form the U.S. rural Midwest, especially in spring and fall; (iv) the soil component has northern sources, with perhaps transpolar and trans-Pacific origins, in spring and summer; and (v) the NOx component appears to be derived from northern sources at polar sunrise in spring.