SULFUR AND REACTIVE NITROGEN-OXIDE FLUXES IN THE NORTH-ATLANTIC ATMOSPHERE

This paper compiles atmospheric budgets for the large-scale cycling of sulfur and reactive nitrogen oxides in the atmosphere of the North Atlantic Ocean, Using model results and measurements reported in the literature, estimates are made of the following large-scale fluxes: eastward from North America into the North Atlantic atmosphere, northward into the Arctic, eastward into and westward out of Europe, westward from Africa, and westward at the Caribbean. Marine emissions into the North Atlantic atmosphere and deposition to the ocean are estimated. Atmospheric transport from continental sources contributes 4.4-7.5 Tg S/yr and 1.7-3.4 Tg N/yr to the North Atlantic Ocean atmosphere, while 0.6-3.6 Tg S/yr comes from marine emissions. Atmospheric transport removes 1.4-1.9 Tg S/yr and 0.5-0.8 Tg N/yr, and deposition to the ocean accounts for 5.2-15.7 Tg S/yr and 1.6-5.7 Tg N/yr. The main input terms for sulfur are flow from North America, followed by marine dimethylsulfide emissions and flow from Africa; for nitrogen, North American and African inputs are comparable. Although outputs exceed inputs for both sulfur and nitrogen, the ranges of estimates overlap by approximately 75%. The spatial distribution of total sulfur deposition flux is generally consistent with known sources and flow regimes except for high values which occur near the European west coast and off the east coast of the Americas south of 30 degrees N. The spatial distribution of total nitrogen deposition flux is more consistent with current knowledge, with the exception of high values across the 0-10 degrees latitude band. The molar sulfur to nitrogen ratio of total deposition exceeds 2 north of 30 degrees N but is close to or below 1 to the south. Both sulfur and nitrogen outputs exceed inputs in the northeastern and southwestern parts of the region, indicating that either inputs from adjacent continents are underestimated or that the deposition is overestimated.