Contribution of Gulf Area Natural Sulfur to the North American Sulfur Budget

To evaluate the contribution of natural sulfur compounds from the Gulf of Mexico to the overall North American sulfur budget, two series of air sampling flights were performed over the gulf area. Total aerosol mass load and sulfate concentration data indicate, in agreement with our previous findings on gas-phase products, that these observations can be divided into two categories. One group of measurements was taken under offshore airflow and the other under onshore flow conditions. From the measurements performed under “clean” (onshore) flow, average inside boundary layer SO₄^2-concentrations were evaluated. Using these data, together with our previously reported dimethyl sulfide levels, we developed a simple model to estimate the sulfur flux transported northward from the gulf area. Upper and lower limits of this contribution are estimated at 0.25 and 0.04 Tg (S) year^-1, respectively. Although this quantity is relatively low compared with the national U.S. anthropogenic emission, it has significance for the global sulfur cycle, and it can cause a significant acidification of cloud water.