Effects of Temperature and Relative Humidity on Laboratory Air Filter Loading Test by Hygroscopic Salts

Abstract Air filters are common control technologies of the atmosphere pollutant, which could be operated under different environments. The operating conditions include different temperatures, relative humidities, and particle states. However, typical filter testing conditions do not strictly regulate the aforementioned parameters; hence there is always a discrepancy between the lab filter testing and the real operating conditions. Air filter loading results are valuable to predict the filter life, whereas it could be affected by testing conditions. In this study, the effects of temperature and relative humidity on the air filter loading by hygroscopic salts were studied. Potassium chloride, ammonium sulfate, and ammonium nitrate are used to represent the dry solid particles and wet particles in the atmosphere. The testing temperature covers from 5 ℃ to 50 ℃ and the testing RH covers from 30% to 75%. Importantly, the absolute humidity is considered in this study, which depends on both temperature and RH. Besides the experiments, the possible reasons that could affect the filter loading were also discussed. Based on the experiment results and theories discussed, it could be concluded that the testing RH is a major factor while the testing temperature is a minor factor, which affects the hygroscopic particle filter loading, regardless of the particle state(dry/wet). This article not only suggests the need of revising current filter testing standards by considering the air filter operating temperature and relative humidity but also offers an insight into how the atmospheric particles hygroscopicity can be linked with ambient particulate matter mitigation technologies.