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 At lantic Ocean, Using model results and measurements reported in the lit erature, estimates are made of the following large-scale fluxes: eastw ard from North America into the North Atlantic atmosphere, northward i nto the Arctic, eastward into and westward out of Europe, westward fro m Africa, and westward at the Caribbean. Marine emissions into the Nor th Atlantic atmosphere and deposition to the ocean are estimated. Atmo spheric 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 remove s 1.4-1.9 Tg S/yr and 0.5-0.8 Tg N/yr, and deposition to the ocean acc ounts for 5.2-15.7 Tg S/yr and 1.6-5.7 Tg N/yr. The main input terms f or sulfur are flow from North America, followed by marine dimethylsulf ide emissions and flow from Africa; for nitrogen, North American and A frican 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 gener ally consistent with known sources and flow regimes except for high va lues which occur near the European west coast and off the east coast o f the Americas south of 30 degrees N. The spatial distribution of tota l nitrogen deposition flux is more consistent with current knowledge, with the exception of high values across the 0-10 degrees latitude ban d. The molar sulfur to nitrogen ratio of total deposition exceeds 2 no rth of 30 degrees N but is close to or below 1 to the south. Both sulf ur and nitrogen outputs exceed inputs in the northeastern and southwes tern parts of the region, indicating that either inputs from adjacent continents are underestimated or that the deposition is overestimated.