Atmospheric sulfur cycle simulated in the global model GOCART: Comparison with field observations and regional budgets

Abstract

Abstract. We present a detailed evaluation of the atmospheric sulfur cycle simulated in the Georgia Tech/Goddard Global Ozone Chemistry Aerosol Radiation and Transport (GOCART) model. The model simulations of SO2, sulfate, dimethylsulfide (DMS), and methanesulfonic acid (MSA) are compared with observations from different regions on various timescales. The model agrees within 30% with the regionally averaged sulfate concentrations measured over North America and Europe but overestimates the SO2 concentrations by more than a factor of 2 there. This suggests that either the emission rates are too high, or an additional loss of SO2 which does not lead to a significant sulfate production is needed. The average wintertime sulfate concentrations over Europe in the model are nearly a factor of 2 lower than measured values, a discrepancy which may be attributed largely to the sea-sak sulfate collected in the data. The model reproduces the sulfur distributions observed over the oceans in both long-term surface measurements and short-term aircraft campaigns. Regional budget analyses show that sulfate production from SO2 o:•idation is 2 to 3 times more efficient and the lifetimes of SO2 and sulfate are nearly a factor of 2 longer over the ocean than over the land. This is due to a larger free tropospheric fraction of SO2 column over the ocean than over the land, hence less loss to the surface. The North Atlantic and northwestern Pacific regions are heavily influenced by anthropogenic activities, with more than 60% of the total SO2 originating f•orn anthropogenic sources. The average production efficiency of' SO2 from DMS oxidation is estimated at 0.87 to 0.91 in most oceanic regions.

Aerosol loading in the Southeastern United States: reconciling surface and satellite observations

“…Simulated summertime enhancements in AOD through the Eastern US range from 15-40 %. While the model does show a summertime maximum in AOD over the Ohio River Valley and Northeastern US associated with increases in sulfate via SO 2 oxidation (Chin et al, 2000) and stagnation events, it does not reproduce the strong observed seasonality in column AOD over the SEUS.…”

Changing concentrations of CO, CH 4 , C 5 H 8 , CH 3 Br, CH 3 I, and dimethyl sulfide during the Southern Ocean Iron Enrichment Experiments

“…It is estimated that a net flux of 2.9 Tg of S per year from DMS oxidation originates from the Southern Ocean south of 40°S (M. Chin, personal communication; ref. 53). If this entire region were to respond as observed during SOFeX, the additional flux of DMS would result in a total emission of 14 Tg of S per year from the Southern Ocean region.…”

Biogenic carbon and anthropogenic pollutants combine to form a cooling haze over the southeastern United States

“…Second, the observed AOT changes seasonally by a factor of 6-7 (summer(JJA)/winter(DJF), AERONET Walker Branch) whereas the sulfate changes seasonally by a smaller factor (Ϸ3) as observed in the eastern U.S. by the Interagency Monitoring of Protected Visual Environments (IMPROVE) network. The IMPROVE sulfate seasonality is generally attributed to faster summertime oxidation of SO 2 through aqueous reactions with peroxides (20). The main source of peroxides is isoprene oxidation in the SE U.S. (21), so we infer that the sulfate seasonality must be linked to BVOC emission and oxidation, but this seasonality is still insufficient to explain the observed AOT changes.…”