Evaluation of Background Odour in Tedlar and Nalophan Sample Bags

Tedlar sample bags are commonly used in North America for collection of odour samples and are a regulatory requirement in some jurisdictions. Experience has shown the residual or background odour in Tedlar bags can influence odour measurements, and that odour concentration of field blanks commonly ranges up to 60 odour units per cubic metre (ou/m3). Background odour of up to 100 ou/m3 in new Tedlar bags has been reported in the literature.Field dilution of odour samples is often required to prevent condensation in the sample bag and, in some jurisdictions (i.e. Ontario, Canada) field dilution ratios as high as 100:1 are needed to meet prescribed pre-dilution requirements. When field dilution is used, the sample evaluated by olfactometry is at a much lower concentration than the original source, and is therefore particularly susceptible to influence of background odour in the sample bag. If unaccounted for, elevated background odour in sample bags could lead to incorrect conclusions that result in unnecessary and costly odour abatement.Nalophan, an alternative sample bag material, has been reported to have lower levels of background odour, and is widely used for odour studies in Europe. Preconditioning procedures have also been reported to reduce the background odour from Tedlar bags. This project was undertaken to investigate the relative performance of Nalophan and Tedlar odour sample bags with respect to background odour. The effects of preconditioning procedures and common labeling methods on background odour were also investigated.The results lead to the conclusion that, with adequate pre-conditioning procedures, both Tedlar and Nalophan sample bags can provide similarly low background odour levels. Tedlar bags must be preconditioned at elevated temperature to minimize background odour. Nalophan bags may be stored in an odour free environment for a period of time to minimize background odour, but this is not always necessary as some batches have minimal background odour on receipt. Without these precautions, there is a potential for excessive background odour to adversely influence the analysis of low level odours.