Comparison of Sampling Resistance for One to Three Sheets of Membrane Type Passive Sampler

Field measurements were conducted using one to three sheets of a poly-tetrafluoroethylene (PTFE) membrane resistance-type passive sampler (N type sampler) and diffusion length resistance-type sampler (O type sampler) to compare sampling resistance. Acidic gases such as nitric acid (HNO₃), hydrochloric acid (HCl), sulfur dioxide (SO₂), ozone (O₃), ammonia (NH₃), nitrogen dioxide (NO₂), and nitrogen oxides (NO X ) were sampled using five types of capturing filter paper: plain polyamide filter ([Greek Phi symbol]47 mm) and cellulose filters ([Greek Phi symbol]14.5 mm) impregnated with NaNO₂ + K₂CO₃, H₃PO₄, triethanolamine (TEA), and TEA + 3-oxo-2-phenyl-4,4,5,5-tetramethylimidazolin-1-oxyl (PTIO). Four sets of the samplers were exposed to the atmosphere for 4 or 5 weeks through four seasons in FY 2006. The amount of gas components captured occurred in the order of NO X > O₃ > NO₂ > NH₃ > SO₂ > HCl > HNO₃ for all of the filters in spring and autumn. However, the amount of NH₃ captured was large in summer and the amount of NO X was large in winter. The relative standard deviations (RSDs) were less than 10% except for NH₃ with the O type sampler in spring and autumn, and for HCl of both type samplers in winter. The RSDs were not dependent on the numbers of PTFE sheets for gas species and season. When the N type sampler mounted on one PTFE sheet was normalized to unit, the resistance values of two and three PTFE sheets for HNO₃ were 2.3-2.4 and 4.2-6.1, respectively, while the values of two and three sheets for SO₂, O₃, HCl, and NH₃, were 1.1-1.5 and 1.3-1.9, respectively. There was little variation in resistance for NO₂ and NO X , as shown by the values of 1.0-1.1 and 0.9-1.2, respectively. For comparison with the O type sampler, the resistances values for SO₂, O₃, HCl, NH₃, NO₂ and NOX were 4.9-5.8, 2.5-3.2, 2.7-4.5, 4.1-12.6, 1.4-1.9, and 1.2-2.4, respectively. The resistance values of the O type sampler were larger than those of the N type samplers. The collection of HNO₃ was decreased 25% per PTFE sheet, while the decreases for SO₂, O₃, HCl and NH₃ were moderate at 12-17%. In contrast, collection of NO₂ and NO X was minimally affected by the number of PTFE sheets. The concentration of HNO₃, SO₂, HCl and NH₃ in the N type passive sampling method was compared with that of the four-stage filter pack method. The passive method for HNO₃, SO₂ and HCl was in fair agreement with the filter pack method. For NH₃, the concentration by passive method was lower than that by the active method.