Evaluation of the capabilities of deposition networks to resolve regional trends and spatial patterns

Abstract

Sulfur emission control programs are being implemented in North America at the same time as budgetary pressures are leading to reduced numbers of stations in acid deposition monitoring networks. In order to assess the effectiveness of emission control programs, it is essential that deposition monitoring networks continue to fulfill their principal goals of detecting and quantifying temporal changes in deposition, and of describing changes in spatial deposition patterns. A set of statistical techniques has been developed and applied to assess the capabilities of the Canadian Air and Precipitation Monitoring Network (CAPMoN) in southeastern Canada according to two performance criteria: (1) the ability of CAPMoN to detect and quantify projected regional trends in precipitation sulfate in a timely fashion, and (2) the ability of CAPMoN to delineate both present and projected future spatial patterns of wet sulfate deposition. In the area of southern Canada now receiving in excess of 20 kg ha −1 yr −1 wet sulfate deposition, the seven CAPMoN stations alone would be able to detect and quantify projected regional trends within one year of the 41 stations now operating in the area. However, in the regions now receiving less than 20 kg ha −1 yr −1 wet sulfate deposition, CAPMoN would require 4–8 yr longer than the larger set of currently available stations to detect projected reductions. The current configuration of CAPMoN is adequate to monitor some areas with sulfate deposition exceeding 20 kg ha −1 yr − until deposition goes below this value, but not those areas situated in extreme southwestern and southeastern Ontario, southern Quebec, and the Bay of Fundy region. In comparison to using all currently operating monitoring stations, using only CAPMoN stations underestimates the area in which wet sulfate deposition exceeds 20 kg ha −1 yr −1.