The transatlantic transport of sulfur

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 [SO₄⁼] 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.