Journal of Geophysical Research: Atmospheres

Sulfate over the North Atlantic and adjacent continental regions: Evaluation for October and November 1986 using a three-dimensonal model driven by observation-derived meteorology

Authors

  • Carmen M. Benkovitz,

  • Carl M. Berkowitz,

  • Richard C. Easter,

  • Seth Nemesure,

  • Richard Wagener,

  • Stephen E. Schwartz


Abstract

A high-resolution three-dimensional Eulerian transport and transformation model has been developed to simulate concentrations of tropospheric sulfate for specific times and locations; it was applied over the North Atlantic and adjacent continental regions during October and November 1986. The model represents emissions of anthropogenic SO2 and sulfate and of biogenic sulfur species, horizontal and vertical transport, gas phase oxidation of SO2 and dimethylsulfide, aqueous phase oxidation of SO2, and wet and dry deposition of SO2, sulfate, and methanesulfonic acid (MSA). The meteorological driver is the 6-hour output from the forecast model of the European Centre for Medium-Range Weather Forecasts. Calculated sulfate concentrations and column burdens, examined in detail for specific dates, are related to existing weather patterns. These quantities exhibit rich temporal and spatial structure; the characteristic (1/e) autocorrelation time for the sulfate column burdens over the central North Atlantic averages 10 hours; 95% of the values are 25 hours or less. The characteristic distance of spatial autocorrelation over this region depends on direction; the minimum value of the average is 900 km and the minimum values for the 10th and 90th percentiles are 400 and 1700 km. Daily average model sulfate concentrations at the lowest vertical level accurately represent the spatial variability, episodicity, and absolute magnitudes of surface concentrations measured by monitoring stations in Europe, Canada, New York state, and Barbados; over 50% of model concentrations are within a factor of 3 of the observations. Over 50% of weekly model sulfate wet deposition amounts are within a factor of 3 of observations from U.S. monitoring stations. Over the 34-day period modeled, contributions from anthropogenic emissions to the sulfate over the mid North Atlantic Ocean ranged from 44 to 66%, contributions from biogenic emissions were between 6 and 12%. Calculated average yields for sulfate (47 to 72%) and MSA (13%), and turnover times for SO2 (2 to 3 days) and sulfate and MSA (4 to 8 days) are comparable to previous estimates; however, these quantities depend on meteorological conditions and on the geographical and vertical distributions of the material.

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