Studies of the effect of humidity and other factors on some different filter materials used for gravimetric measurements of ambient particulate matter

The results from studies of the effects of several factors on the accurate measurement of particulate matter (PM) mass collected on ambient air monitoring filters are described. The main investigation quantifies the effect of humidity on the mass of blank filters of some commonly used materials in Europe, namely quartz fibre, glass fibre and PTFE-bonded glass fibre. Supplementary work investigates the effect of humidity on the mass of sampled PM, and effects of storage and transport are also reported.A number of fundamental problems associated with the weighing of filters are quantified and, for the materials and factors studied, we conclude that quartz filters are less well suited to high accuracy determinations of PM mass than glass fibre filters, while PTFE-bonded glass fibre filters are better than both. Though other factors also have an important role in the choice of filter material, we believe that the results form a useful addition to the limited amount of information available in this area.