The transatlantic transport of sulfur

ABSTRACT This paper examines the transport of North American sulfur emissions across the North Atlantic Ocean to Europe. A review of available precipitation sulfate data from the North Atlantic and adjacent coastal regions yields a concentration field which is consistent with known source distributions and meteorological factors. The marine background precipitation excess sulfate concentration is found to be 6–8 μeq 1−1 and [SO4*] to decrease from >50 μeq 1−1 with offshore flows at the North American east coast to 8–15 μeq 1−1 with onshore flows at the European west coast. This decay is consistent with a distance constant of 2400 km and a residence time of ˜80 h, and in turn, corresponds to a transatlantic flux of anthropogenic sulfur of 0.3‐0.4 Tg a−1. A second independent estimate, based on the application of a climatological dispersion model, which accounts for long‐term average diffusion, wet and dry deposition, and SO2 to SO4= transformation, yields a flux of North American anthropogenic sulfur at the European west coast of 0.2 Tg a−1, in agreement with the first estimate. At the distance of the European west coast, North American anthropogenic emissions account for ca. 4 μeq S 1−1 in precipitation—less than the marine background of 6–8 μeq 1−1, and much less than the annual average [4=*] value of ca. 30 μeq S 1−1 appropriate for much of the coastal region. It is concluded that, on average, the amount of North American anthropogenic sulfur reaching Europe is small compared to that from other sources.