Abstract
Conventional denuders made of glass or metal are too heavy and bulky to be used in personal sampling systems. In this study, a portable Porous Membrane Denuder (PMD) was developed for personal sampling. The PMD utilizes the porosity of the membrane material and a configuration of multiple parallel flow channels to reduce the size and weight of the device, while increasing the gas collection efficiency. Four types of PMDs (PMD I, II, III and IV) with increasing numbers of channels and smaller channel openings were constructed and tested. Using 10% sodium carbonate coating and a feed concentration of 1 ppm, PMD Ia's collection efficiency for sulfur dioxide over 8 hours was higher than 99.9%. For a feed concentration of 10 ppm, the 5-hr time-weighted-average collection efficiency for sulfur dioxide was 73.1%, 82.8%, 90.9%, 97.2% for PMD Ib, II, III and IV, respectively, compared with 96.6% of the Glass Honeycomb Denuder (GHD), which has similar structure to PMD IV. However, the weight of PMD IV is only one-tenth of that of the GHD. It is clear that with a similar physical structure, PMDs have similar capacities to traditional Glass Honeycomb Denuders, yet are much lighter and less expensive. This study demonstrates the great potential of this new type of denuder for many applications in the field of environmental and industrial hygiene monitoring. Particle loss fractions of the four types of PMDs in the size range of 1 to 10 μm were also measured and were 2.9%, 5.2%, 5.7% and 7.3%, respectively.
Highlights
Diffusion denuders are well established devices to remove gases from ambient air (Dasch et al, 1989; Huang et al, 2004; Tsai et al, 2004; Acker et al, 2005; Hayami 2005; Pathak and Chan, 2005)
The low exhaust concentration means that the denuder has collection efficiency higher than 99.9% for the entire eight hours
Our results demonstrate that the Porous Membrane Denuder (PMD) has a capacity that is high enough to be used for ambient SO2 sampling
Summary
Diffusion denuders are well established devices to remove gases from ambient air (Dasch et al, 1989; Huang et al, 2004; Tsai et al, 2004; Acker et al, 2005; Hayami 2005; Pathak and Chan, 2005). The inner surface of the flow path is coated with a material that absorbs a particular gas or vapor. When air passes through the denuder, gas molecules diffuse to the surface of the flow path and get absorbed on the coated surface. Because of the gas removal capability, denuders have been used to measure the concentrations of gases in sampled air. They have been used to remove gases or vapors from an aerosol stream to prevent their interference in aerosol measurement that can cause positive or negative sampling artifacts (Hinds, 1999; Keck and Wittmaack, 2006).
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