Vertical variability of seawater DMS in the South Pacific Ocean and its implication for atmospheric and surface seawater DMS

Shipboard measurements of atmospheric dimethylsulfide (DMS) and sea surface water DMS were performed aboard the R/V Onnuri across the South Pacific from Santiago, Chile to Fiji in February 2000. Hydrographic profiles of DMS, dissolved dimethylsulfoniopropionate (DMSP(d)), and particulate DMSP(p) in the upper 200m were obtained at 16 stations along the track. Atmospheric and sea surface water DMS concentrations ranged from 3 to 442pptv and from 0.1 to 19.9nM, respectively; the mean values of 61pptv and 2.1nM, respectively, were comparable to those from previous studies in the South Pacific. The South Pacific Gyre was distinguished by longitudinal-vertical distributions of DMS, DMSP(d), and DMSP(p), which was thought to be associated with the characteristic modification of biological activities that occurs mainly due to significant change in water temperature. The averaged DMS maximum appeared at 40m depth, whereas DMSP(p) and DMSP(d) maxima coincided with that of dissolved oxygen content at 60-80m. The sea-to-air fluxes of DMS were estimated to be 0.4-11.3micromold(-1)m(-2) (mean=2.8micromold(-1)m(-2)). A fairly good correlation between atmospheric DMS and sea-to-air DMS flux indicated that atmospheric DMS concentration was more sensitive to change in physical parameters than its photochemical removal process or surface seawater DMS concentrations.

A review of methods for the determination of reduced sulfur compounds (RSCs) in air

The importance of reduced sulfur compounds (RSCs) in air is well-known for its significant effect on global atmospheric chemistry and malodor and quality of life. In this review, methodological approaches commonly employed for the analysis of RSCs such as hydrogen sulfide, methane thiol, dimethyl sulfide, carbon disulfide, and dimethyl disulfide in air are described. To this end, we focus on gas chromatography (GC) because it is the most feasible, frequently used, and widely accepted approach for the analysis of RSC in air. The advantages and possible limitations related to sampling and/or preconcentration methods are also discussed. The relative performance of different GC-based detection methodologies is evaluated in terms of basic quality assurance. Some alternative methods (i.e., other than GC) that deal with the determination of RSCs in air matrices are also discussed briefly. Finally, this review addresses the methodological developments of RSC analysis by highlighting current limitations and future developments.

Dimethylsulfide and its oxidation products in coastal atmospheres of Cheju Island

The concentrations of dimethylsulfide (DMS) in air and its oxidation products in aerosols were measured from the coastal atmospheres of Cheju Island, Korea, during three exploratory field experiments conducted over September 1997 through April 1998. According to our measurements, there were large fluctuations in the distribution of DMS and relevant species in the coastal atmospheres; the magnitude of variations was significant both within each measurement period and across different measurement periods. The mean mixing ratios of atmospheric DMS from the whole data sets were found within the range of 19 to 1140 pptv (n=84) with the grand mean value of 100 pptv. Like DMS, large variations in the data distribution were consistently seen from other species investigated concurrently. The concentrations of aerosol ions including non-seasalt sulfate (NSSS), seasalt sulfate (SSS), and methane sulfonate (MSA) spanned over two orders of magnitude such as 0.24-88 (mean 32), 0.08-17.2 (mean 3.70), and 0.01-0.78 (mean 0.16) nmol m(-3), respectively. The molar ratios of those ions were measured as: (1) NSSS/SSS in 1.26-95 (mean 44); (2) MSA/NSSS in 0.0002-0.063 (mean 0.009); and (3) NSSS/NO(3) in 0.21-9.5 (mean 2.35). Examinations of our measurement data indicated that the concentrations of DMS and relevant ions varied significantly across day/night periods and across different seasons. It was also seen that there are strong differences in seasonal distribution patterns between fall, winter, and spring. Detailed analysis of the data sets revealed that changes in their distribution patterns were in strong compliance with changes in meteorological conditions. Especially, large fluctuations in magnitudes and amplitudes of springtime DMS concentrations were coinciding with the intrusion of southeasterly winds, suggesting the possibility that the DMS-rich air masses were brought into the study area from the productive waters of the southeast coastal area of Cheju. Similarly to the case of DMS, the occurrence of unusual wind patterns during spring contributed to changes in the content and composition of aerosol ions. Although the introduction of southeasterly winds during spring helped maintain high DMS and MSA levels, the concentrations of aerosol ions dropped significantly because of depositional loss during the passage of air mass over land area. According to the procedures of Wylie and De Mora, we reached the conclusion that the magnitude of annual DMS emissions in the western Korean sea were in the range of 5 to 18 Gg S.