Continuous measurement of atmospheric reduced sulphur compounds as key tracers between odour complaints and source apportionment.

Odour complaints are frequent nowadays, particularly nearby industrial facilities emitting odorous compounds. Among all compounds susceptible of causing odour annoyance, reduced sulphur compounds (RSC) were studied, due to their unpleasant odour and low odour threshold. RSC ambient air mixing ratios, meteorological conditions and population complaints were analysed in an area of complex topography in order to identify their potential sources. Mixing ratios of three compounds, dimethyl sulphide (DMS), carbon disulphide (CDS) and dimethyl disulphide (DMDS), were continuously monitored using an online gas chromatograph coupled with a mass spectrometer detector (GC-MSD), which was placed in a mobile air quality monitoring unit. Measurement campaigns were performed during 2012 and 2013 for periods of 7-25 days in an urban area (four campaigns, N = 1368) and an urban area surrounded by industrial activities (three campaigns, N = 564). During such campaigns, RSC mixing ratios were frequently above their odour thresholds, which did not always involve citizen complaints. Average RSC ambient air mixing ratios tended to be lower in the urban area (DMS 0.06-0.33, CDS 0.05-0.10, DMDS 0.07-0.30 μg m-3) than in the industry surrounded one (DMS 0.30-2.39, 0.05-0.18, DMDS 0.09-0.62 μg m-3). The DMS/DMDS mixing ratio was frequently above 1, being a paper mill one of the main sources of RSC in the area. DMS/DMDS ratios below 1 were also recorded, suggesting a waste treatment plant as the RSC source or older air masses coming from the paper mill.