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 (FO)-stage filter in a four-stage filter-pack method. A four-stage filter-pack method can completely collect sulfur species (SO_2 and SO_4~(2-)), nitrate species (HNO_3 and NO_3), and ammonium species (NH_3 and NH_(4+)) 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 NO_3, the PTFE filter was more vulnerable than the quartz filter at air temperatures below 21℃, while the quartz filter was more vulnerable than the PTFE filter at air temperatures exceeding 21℃. A similar vulnerability for air temperature was observed for NH_4~+, although the threshold air temperature was 23℃ for NH_4~+. Consequently, the evaporation loss of NO_3 would be mainly attributable to the volatilization of NH_4NO_3, although it is also partially due to the volatilization of NH_4C1.