Removal efficiency of bimodal PM_2.5 and PM₁₀ by electret respirators and mechanical engine intake filters

As China is receiving an economic boom, PM (particulate matter) pollutions not only have become a serious regional problem but also frequently impacted its neighboring counties, e.g., Korea and Japan. In addition to its adverse effects on human health, the on- and off-road engines operated in ambient can also be affected. In this study, a simple system for generating simulated ambient bimodal PMs comprising fine (PM_2.5), coarse (PM_2.5–10) particles was developed for evaluating the initial efficiency of seven respirator and four engine intake filters. In addition to the size fractional efficiency curves for each filter media determined from the SMPS (scanning mobility particle sizer) and APS (aerodynamic particle sizer), both number and mass based efficiency of these filters for PM_2.5, PM_2.5–10 and PM₁₀ were also obtained to evaluate their performances against ambient PM pollutions. Data showed that the engine intake filters had a low efficiency for both mass and number based PM_2.5, which was only about 25–30%. However, there was a large difference between their number and mass based PM₁₀ efficiency. The former was much lower than the latter because these filters are with high efficiency only for coarse particles. Besides, the most of particles in number was resided in the fine size range while the mass was in coarse size range. For the respirator filtration tests, results showed that most of them can effectively remove both PM_2.5 and PM₁₀, in which the mass efficiency was always higher than that of number. The PM_2.5 number efficiency results showed there are three out of seven respirator filters are with N-95 rated level, in which the efficiency of their most penetrating particle size is higher than 95%. The current simple experimental system could be applied to examine different purpose filters which protect human health and outdoor engines against ambient PM_2.5 and PM₁₀.