Wet Deposition Maps

Patterns of wet deposition of the nitrate/sulfate/ammonium ion across eastern Canada and the United States are based on measurements of precipitation depth and nitrate/sulfate/ammonium concentrations in precipitation samples. These measurements were collected and quality controlled by their respective networks: in Canada, the federal Canadian Air and Precipitation Monitoring Network (CAPMoN) and provincial or territorial networks in Alberta, New Brunswick, the Northwest Territories, Nova Scotia, Ontario and Quebec. In the United States, wet deposition measurements were made by two coordinated networks: the National Atmospheric Deposition Program (NADP) / National Trends Network (NTN) and the NADP/Atmospheric Integrated Research Monitoring Network (AIRMoN). Total annual deposition from each site was screened for completeness using the following criteria: (1) Precipitation amounts were recorded for >90% of the year and >60% of each quarter, and (2) a nitrate/sulfate/ammonium concentration was reported for >70% of the precipitation measured over the year and for >60% of each quarter. Only data from sites that had been designated as regionally representative were used in the mapping. Annual deposition amounts were interpolated using ordinary kriging using ArcMap Geostatistical Analyst. The map is limited to the contiguous U.S. and southeastern Canada because outside that region, the interpolation error exceeds 30% due to the larger distances between stations.