Fig. 2 summarized the average removal efficiency (RE) of PM2.5. The graph included the RE of the cross-check periods. All RE of these pre-testing are close to zero and this is important to ensure that the two sensors were consistent in measuring PM2.5. The solid bar indicated the standard deviation (SD). The length of each bar is equal to 2 units of SD. The overall RE of used masks was 74 ± 10%. The RE of washed masks was 82 ± 12%. The REs of washed and used masked are smaller than the new masks of the same brands about 10% to 20% as presented in Fig. 3.
With unit mounting the mask had the fan speed variable. Fig. 3 presented the RE of AQBlue masks with new, used, and washed conditions in four fan duty cycles with 100% as the maxium speed and so that flow rate through each mask. With each condition, the higher flowrate showed a slight improvement to remove PM2.5. These improvement is only moderate in compared with the efficiency with different PM2.5 concentration. One obvious limitation to analyze fan duty in this experiment is unrealistic to the human breath in the flow and the rhythm. According to Wikipedia, an average person takes 12 breaths a minutes with 0.5L each. This study only be able to evaluate relative flowrate to RE and not able to measure the real flowrate and the effect of rhythm or breath cycle to the RE.
Alternatively, RE of masks were compared with the same flowrate in 4 modes as shown in Fig. 5. The Re of new masks shown a better removal than washed and used one with the PM2.5 in range of 0 to 200 µg/m3.
In addition, comparing used masks from two main brands supplying dedicated PM2.5 masks: AQBlue and Airphin, the RE was a mixed with a larger range of RE by AQBlue and overlaping with Airphine's. These could be an artifact that more AQBlue masks are tested (3) than Airphin (2).