Fate of volatile sufur compounds in odour bags

Abstract

Complaints due to odours are a major issue for many industrial as well as agricultural facilities. Repeated release of unpleasant odours from these facilities can constitute both a public nuisance and a possible regulatory violation. Amongst the most common odorous emissions, volatile sulfur compounds (VSCs) are the most malodorous, have very low odour threshold values, and in many cases are the dominant odorants. For odour assessment, VSC containing air samples are commonly collected using plastic bags. However, VSC odorants are unstable and often suffer losses during storage in the sample bags. The degree of VSCs losses depends on many factors such as storage time, bag materials, temperature, sample relative humidity, light exposure, and the presence of volatile organic compounds (VOCs). To assess the impact of storage factors on the stability of VSC odorants, laboratory-based experiments were performed according to a factorial experimental design. Linear mixed-effects models of the storage recoveries for 10 VSC odorants in 3 different bag materials were constructed. The 10 VSCs included hydrogen sulfide, methanethiol, ethanethiol, dimethyl sulfide, tert-butylthiol, ethyl methyl sulfide, 1-butanethiol, dimethyl disulfide, diethyl disulfide, and dimethyl trisulfide. The 3 bag materials chosen in this work were Tedlar, Mylar, and Nalophan. Analyses of the results suggested Tedlar as the material of choice for the storage of VSC odorants. This material is superior over Mylar and Nalophan in maintaining the stability of all the 10 VSCs as well as the integrity of the VSC compositions. Based on the outcome of the recovery projection from the mixed models, recommendations for the handling/storage of VSC containing air sample bags are produced. It is recommended that VSC containing samples in plastic bags should not be stored at a temperature higher than 20oC and be covered from light. Under those conditions, VSC samples in Tedlar bags can be stored up to 18 hours whereas in Mylar and Nalophan, the storage time should not exceed 12 hours.