Department of Earth System Science

Measurements of atmospheric dimethylsulfide (DMS), hydrogen sulfide (H₂S), and carbon disulfide (CS₂) were made over the North and South Atlantic Ocean as part of the Global Tropospheric Experiment/Chemical Instrumentation Test and Evaluation (GTE/CITE 3) project. DMS and CS₂ samples were collected and analyzed using an automated gas chromatography/flame photometric detection system with a sampling frequency of 10 min. H₂S samples were collected using silver nitrate impregnated filters and analyzed by fluorescence quenching. The DMS data from both hemispheres have a bimodal distribution. Over the North Atlantic this reflects the difference between marine and continental air masses. Over the South Atlantic it may reflect differences in the sea surface source of DMS, corresponding to different air mass source regions. The median boundary layer H₂S and CS₂ levels were significantly higher in the northern hemisphere than the southern hemisphere, reflecting the higher frequency of samples influenced by pollutant and/or coastal emissions. Composite vertical profiles of DMS and H₂S are similar to each other, and are consistent with a sea surface source. Vertical profiles of CS₂ have maxima in the free troposphere, implicating a continental source. The low levels of H₂S and CS₂ found in the southern hemisphere constrain the role of these compounds in global budgets to significantly less than previously estimated.