Determination of irreversible absorption of water by cellulose filters

Abstract

Using cellulose filters instead of glass fiber for the determination of the total suspended particulates by the “High-Vol” method may cause significant positive errors. Because of their hygroscopic nature, cellulose filters absorb a large quantity of water during sampling which is not entirely lost on equilibration at constant humidity. For short period samples, the amount of water irreversibly absorbed, strongly depends on the atmospheric humidity. For a 1-h filter taken on a foggy day, this amount of water may be of the same order or even higher as an average particulate load obtained by commercial “High-Vol” samplers in urban areas. For 24-h sampling periods, a mean correction factor was determined during various atmospheric conditions. This value amounted to 4.2 ± 2.4 mg on the average for an 11 cm dia. Whatman 41 filter (0.8 g of cellulose) at a mean atmospheric humidity of 90 per cent.