SOURCE APPORTIONMENT OF WET SULFATE DEPOSITION IN EASTERN NORTH-AMERICA

An analytical model of long distance transport of air pollutants (Fay and Rosenzweig, 1980, Atmospheric Environment 14, 355-365) has been adapted for the estimation of long term (e.g. annual) wet sulfate deposition in eastern N America. The model parameters have been optimized for best agreement with 1980-1982 measurements at 109 monitoring sites in this region. The root mean square residual of the model and measurement comparison is 4 kg ha-1 y-1 (17% of the mean measured value). Transfer coefficients were found to decrease exponentially with source-receptor distance, having length scales between 1100 and 400 km depending upon whether the source is upwind or downwind of the receptor. Source apportionment calculated for four sites from this model shows that about half of the deposition is due to 7-8 of the largest source contributors to each site (aggregated to the state and sub-province level). A 17-year record of precipitation sulfate measured at Hubbard Brook, New Hampshire, compares favourably with the model calculation. Calculated USA-Canada transboundary fluxes differ from previous estimates. Isopleths of 1980-82 yearly depositions were determined. A proposed 45% reduction in USA sulfur emissions was found to produce about a 35% reduction of deposition at environmentally sensitive areas in the USA and Canada.