Ocean-atmosphere interactions in the global biogeochemical sulfur cycle

Workbook of atmospheric dispersion estimates

Nd and Sr isotopic characteristics of Chinese deserts: Implications for the provenances of Asian dust

A three-dimensional model is used to simulate the global tropospheric distributions of dimethylsulfide (DMS), SO2, SO42−, and methanesulfonic acid (MSA). The model uses meteorological input from a general circulation model (GCM) developed at the Goddard Institute of Space Studies (GISS) with 4° × 5° horizontal resolution, nine layers in the vertical, and a time resolution of 4 hours. Model results are compared with observations from surface sites, ships, and aircraft. The model reproduces generally to within 30% the observed SO2 and SO42− concentrations over the United States and Europe; these concentrations are highly sensitive to the supply of H2O2 as an in-cloud SO2 oxidant. Sulfate concentrations and wet deposition fluxes observed at remote marine sites can be accounted for using a global DMS source of 22 Tg S yr−1 in the model. However, this source overestimates DMS air concentrations by a factor of 2 unless we assume the presence of another DMS oxidant besides OH and NO3. Inclusion of another DMS oxidant in our model also improves the simulation of the MSA to SO42− concentration ratio in marine air. Simulated SO42− concentrations in the northern hemispheric free troposphere are much lower than in previous global models and are more consistent with the few observations available. The difference reflects in part our accounting of efficient scavenging of SO2 and SO42− in wet convective updrafts. Global mean tropospheric lifetimes computed in our model are 1.0 days for DMS, 1.2 days for SO2, 3.9 days for SO42−, and 6.2 days for MSA. Fossil fuel combustion and industrial activities represent 68% of global non-sea-salt sulfur emissions. About 50% of SO2 globally is converted to SO42− aerosol (principally by in-cloud oxidation) while the remainder is removed by deposition (30% by dry, 20% by wet). In-cloud oxidation of SO2 represents 85% of the global SO42− source.

/pdf/a-global-three-dimensional-model-of-tropospheric-sulfate-56hj8t6zz5.pdf

A global three‐dimensional model of tropospheric sulfate

Contributing Authors A. Ackerman, P. Adams, P. Austin, R. Boers, O. Boucher, M. Chin, C. Chuang, B. Collins, W. Cooke, P. DeMott, Y. Feng, H. Fischer, I. Fung, S. Ghan, P. Ginoux, S.-L. Gong, A. Guenther, M. Herzog, A. Higurashi, Y. Kaufman, A. Kettle, J. Kiehl, D. Koch, G. Lammel, C. Land, U. Lohmann, S. Madronich, E. Mancini, M. Mishchenko, T. Nakajima, P. Quinn, P. Rasch, D.L. Roberts, D. Savoie, S. Schwartz, J. Seinfeld, B. Soden, D. Tanre, K. Taylor, I. Tegen, X. Tie, G. Vali, R. Van Dingenen, M. van Weele, Y. Zhang

/pdf/aerosols-their-direct-and-indirect-effects-5d3uwy3f9v.pdf

Aerosols, their Direct and Indirect Effects

Hydrogen peroxide and other atmospheric trace gases were measured along the 91°30′ meridian from near the Iowa border to the Gulf of Mexico during February 1987. The measured H2O2 values were within the range of <0.1 to 1.0 ppbv and an increase in concentration from north to south of 0.04-0.05 ppbv per degree of latitude was observed on five of six flights. The concentration of H2O2 appeared to be primarily dependent upon air mass history; concentration discontinuities were observed when the aircraft flew across air mass boundaries. H2O2 measurements during flights in air masses of similar histories during daylight and night showed no significant difference in concentration. Neither was there a consistent dependence of the H2O2 concentration upon altitude.

Hydrogen peroxide in air during winter over the south‐central United States

Sulfur dioxide (SO2) was measured with a pulsed fluorescence analyzer and filter pack system from the instrumented NOAA King Air aircraft. The measurements were part of the GCE/CASE/WATOX project in July 1988 and included a series of eight flights of 4-hour duration each. During the first four flights the atmosphere was sampled over the Atlantic Ocean within 250 km east of Newport News, Virginia; during the remaining four flights the atmosphere in the vicinity of Bermuda was sampled. SO2 data were collected at two elevations: about 750 mbar in the free troposphere (FT), and in the lower part of the boundary layer (BL) at about 1000 mbar. Average BL concentrations were almost 10 times greater near the east coast than near Bermuda (500±800 pptv versus 60±40 pptv). FT concentrations near the east coast also were greater than near Bermuda but by a lesser factor (110±50 pptv versus 70±40 pptv). The data from the continuous analyzer compared favorably with the data obtained from filter samples collected concurrently. SO2 data from this study are somewhat lower (factor of 0.6-0.9) than previous measurements at both sites. Average concentrations of SO2 measured near Bermuda (60 pptv) were in the range of those observed in the remote marine atmosphere, although higher SO2 concentrations (up to 450 pptv) were also detected on occasion. The SO2 removal rate over the western Atlantic Ocean, near the east coast, is estimated empirically at 0.07±0.03 hour−1. Analyses of the known removal mechanisms suggested that the main removal mechanism is dry deposition.

Sulfur dioxide over the western North Atlantic Ocean during GCE/CASE/WATOX

Dimethyl sulfide and anthropogenic pollutants were measured over the western Atlantic Ocean during January and February 1986, 50 to 150 km east of Boston, MA and in the vicinity of Bermuda in June 1986. The highest DMS concentration measured in the vicinity of Boston was 18 pptv; all other values within the mixed layer (ML) were between 0.5 and 12 pptv. The free troposphere (FT) values were 0.5–5.0 pptv. Sea to air fluxes were estimated at 36 to 66 ng m−2 min−1. FT values measured near Bermuda were 1–17 pptv, and most values were <10 pptv. The Bermuda ML values (35–195 pptv) were as much as 10 times greater than those found near Boston. A steep vertical gradient was observed within the ML in the mid-ocean measurements, indicating that DMS removal rates were faster than the ML mixing times. Several variables may be of consequence in the differences observed between the Boston and Bermuda measurements; the most important of these appear to be the air mass travel time over the ocean and the sea surface temperature.

Dimethyl sulfide over the western Atlantic Ocean

A Beechcraft King Air and a Lockheed WP-3D (P-3) Orion aircraft were flown side by side on January 8, 1986 near Boston, Massachusetts, to compare the scientific measurements being made using the two platforms. The King Air was also flown in formation with a Beechcraft Queen Air and Douglas DC-3 on March 1, 1986 near Raleigh, North Carolina, for the same purpose. This paper summarizes the results of these comparison flights and discusses the scientific measurements made by the aircraft. The accuracies and response times of the aircraft instrumentation are estimated.

C. C. Van Valin

Papers

Hydrogen peroxide in air during winter over the south‐central United States

Sulfur dioxide over the western North Atlantic Ocean during GCE/CASE/WATOX

Dimethyl sulfide over the western Atlantic Ocean

In-flight intercomparisons of some aircraft meteorological and chemical measurement techniques

Cloud nucleus formation in a power plant plume