Assessment of reduced sulfur compounds in ambient air as malodor components in an urban area

Long-term monitoring of reduced sulfur compounds (RSCs: hydrogen sulfide (H2S), methanethiol (CH3SH), dimethyl sulfide (DMS), and dimethyl disulfide (DMDS)) in ambient air was made using an on-line GC system at an odor monitoring station in the city of Ansan, South Korea (August 2005–December 2007). The results were examined to assess the status of RSC pollution, its relative contribution to malodor, and the controlling factors of its occurrence. H2S (mean of 0.27 ppb) was eminent in terms of both magnitude and occurrence frequency, while others were not with mean values of 0.11 (DMDS), 0.10 (DMS), and 0.07 ppb (CH3SH). Unlike others, the temporal trends of H2S were best represented by the combined effects of its source processes and meteorological conditions. The results of correlation analysis indicate strong correlations between RSCs and water-related parameters (e.g., rainfall, dew point, and relative humidity). The role of RSCs as malodor component appears to be pronounced during nighttime, especially in summer. If the relative contribution of RSCs to malodor is assessed by means of the sum of odor intensity (SOI), its impact is relatively low, with an SOI value of 1.22 (weak odor strength). Consequently, a more deliberate approach may be needed to effectively assess odor occurrence patterns in ambient air.