Difference in the Use of a Quartz Filter and a PTFE Filter as First-Stage Filter in the Four-Stage Filter-Pack Method

摘要

We evaluated the differences in the use of a quartz filter and a polytetrafluoroethylene (PTFE) filter as a first (F0)-stage filter in a four-stage filter-pack method. A four-stage filter-pack method can completely collect sulfur species (SO₂ and SO₄2−), nitrate species (HNO₃ and NO₃−), and ammonium species (NH₃ and NH₄+) with little or no leakage irrespectively of the first-stage filter used. On the other hand, a seasonal variation was observed in the efficiency of collection between the quartz filter and the PTFE filter depending on the material to be collected. There was no seasonal variation in the efficiency of collection in sulfur species; in contrast, a clear seasonal variation was observed for the nitrate and ammonium species. As for NO₃−, the PTFE filter was more vulnerable than the quartz filter at air temperatures below 21°C, while the quartz filter was more vulnerable than the PTFE filter at air temperatures exceeding 21°C. A similar vulnerability for air temperature was observed for NH₄+, although the threshold air temperature was 23°C for NH₄+. Consequently, the evaporation loss of NO₃− would be mainly attributable to the volatilization of NH₄NO₃, although it is also partially due to the volatilization of NH₄Cl.