Abstract
Shipboard measurements of atmospheric and seawater DMS were made at 12°S, 135°W for 6 days during March 1992. The mean seawater DMS concentration during this period was 4.1 ± 0.45 nM (1σ, n = 260) and the mean atmospheric DMS mole fraction was 453 ± 93 pmol mol−1 (1σ, n = 843). Consistent atmospheric diel cycles were observed, with a nighttime maximum and daytime minimum and an amplitude of approximately 85 pmol mol−1. Photochemical box model calculations were made to test the sensitivity of atmospheric DMS concentrations to the following parameters: 1) sea‐to‐air flux, 2) boundary layer height, 3) oxidation rate, and 4) vertical entrainment velocities. The observed relationship between the mean oceanic and atmospheric DMS levels require the use of an air‐sea exchange coefficient which is at the upper limit end of the range of commonly used parameterizations. The amplitude of the diel cycle in atmospheric DMS is significantly larger than that predicted by a photochemical model. This suggests that the sea‐to‐air DMS flux is higher than was previously thought, and the rate of daytime oxidation of DMS is substantially underestimated by current photochemical models of DMS oxidation.
Highlights
Introduction variabilityin DMS in the equatorialPacifictropicaltradewindDimethylsulfideis the principlegaseousprecursorfor sulfate aerosoloverthe oceans,and it has been suggestedthat various Ibedbackloops may link DMS emissionsand global climate [Nguyenet al., 1983;Shaw,1983;Chartsonet al., 1987;Bateset al., 1987; Legrand et al, 1988, 1991]
A glasstee containingsilanized theMAGE station.A temperaturienversioncanbe seenat 2200 glasswoolwasfittedwith a septurn.The standardwasinjected m alongwith a sharpdecreasien relativehumidityi,ndicating ontothe glasswool,anda streamof zeroairwaspassedthrough thetopof the cloud-containinlagyerandthebottomofthetrade the tee,wheretheDMS wasentrainedandanalyzedasdescribed wind inversion
- 4, I, I, I, I, I, I, I, The magnitudeof the oceanicsourceof DMS at the MAGE station can be estimated from the observed sea surface concentrationwsin, dfield,andtemperatureW. e usethegeneral
Summary
Dimethylsulfideis the principlegaseousprecursorfor sulfate aerosoloverthe oceans,and it has been suggestedthat various Ibedbackloops may link DMS emissionsand global climate [Nguyenet al., 1983;Shaw,1983;Chartsonet al., 1987;Bateset al., 1987; Legrand et al, 1988, 1991]. DMS e'xhibitsdiel cyclesof considerablaemplitude Experimental Methods becauseof its relatively shortlifetime and photochemicaslink These diel cycleshave been observedby severalinvestigators AtmosphericDMS (RosenstielSchoolof Marine and [Maroulis and Bandy, 1977; Andreae and Raemdonck,1983; AtmosphericScience) Andreaeet al., 1985,'Saltzmanand Cooper,1988; Cooperand. Parameterizationsof its air-sea fluxes and atmospheric The oxidantfree air was drawnIn:stthrougha Teflontube at reactivity In this studywe presentmeasurementsof the diel -20øCcontainingTeflonwoolto removewaterandthenthrough anothertube containingTenax at -20øCto trap DMS. A glasstee containingsilanized theMAGE station.A temperaturienversioncanbe seenat 2200 glasswoolwasfittedwith a septurn.The standardwasinjected m alongwith a sharpdecreasien relativehumidityi,ndicating ontothe glasswool,anda streamof zeroairwaspassedthrough thetopof the cloud-containinlagyerandthebottomofthetrade the tee,wheretheDMS wasentrainedandanalyzedasdescribed wind inversion. This layer is highlystratifiedand actsas a above. SST27 significantdiel variabilityin the sea-to-airflux estimatesas discussed below
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