Development of Beta Attenuation PM2.5 Hourly Monitoring Method Equipped with Unheated Dryer and Its Association with Reference and Equivalent Methods

• Published in: Journal of Japan Society for Atmospheric Environment / Taiki Kankyo Gakkaishi Vol. 56; no. 5; pp. 85 - 95
• Main Authors: Takahashi, Katsuyuki, Takami, Akinori, Tanabe, Kiyoshi, Fushimi, Akihiro
• Format: Journal Article
• Language: Japanese
• Published: Japan Society for Atmospheric Environment 28.07.2021; 公益社団法人 大気環境学会
• Subjects: beta attenuation monitor; dehumidification; federal reference method (FRM); ionic species; particle mass; PM2.5 automated monitor
• ISSN: 1341-4178; 2185-4335
• DOI: 10.11298/taiki.56.85

Hourly PM2.5 monitoring throughout Japan is performed using PM2.5 automated monitors that are designated as equivalent to the reference method (FRM: federal reference method) which is based on the daily average filter weights in the dry state. However, the equivalence of the hourly PM2.5 data has not been approved. Therefore, PM2.5 monitors, which can accurately measure 1-h PM2.5 values, are required. We have developed an unheated dryer-based PM2.5 monitor (NIES-PM25). Our instrument consists of an unheated beta attenuation monitor and a drying system of either a dryer-method (60-min sampling, 1-h value), 3-fold dilution method (120-min sampling, 2-h value), or after-drying method (40-min sampling, 1-h value). We have evaluated the NIES-PM25 through parallel measurements of the atmosphere with FRM and an equivalent (control) PM2.5 monitor in four seasons. The NIES-PM25 was able to always maintain the sample air in the dry state, and neither a significant loss of volatile components nor insufficient dehumidification, which are the concerns with equivalent heated PM2.5 monitors, occurred. The measured values of NIES-PM25 with three drying systems agreed with each other, however, the values were about 16% higher than those of the FRM and the equivalent monitor on average. This is likely due to evaporation of volatile components during a one-day sampling in the FRM and the equivalent monitor is adjusted to the FRM. The dryer method seems to be the best because it can measure 1-h values, but the 3-fold dilution method and after-drying method have size and cost advantages. The NIES-PM25 may contribute to improving the accuracy of 1-h the PM2.5 measurements and to evaluate and improve the accuracy of conventional equivalent monitors.