The setup for testing used massk were identical to this experiment. In summary, two low-cost PM2.5 PMS7003 (Plantower) monitored the background and after filtering PM2.5 concentration. Before testing, the two sensors were both measuring the background concentration for a cross-check. The removal efficiency (RE) was calculated in percent of PM2.5 removed in filtered air in compared to the background concentration.
The masks are mainly from AQBlue brand with one Airphin masks. This mask showed efficacy to removal PM2.5 and in par with Airphin's, another brand supplied a dedicated facemasks against fine particulates. The masks were used for 2-3 weeks before testing for RE and then washed, air-dried and testing again.
Each test lasted about 2 days with fan duty varied from 25% to 100% by automating a target fan duty with the up-time counter by a NodeMCU, a popular microcontroller used in Internet of Things (IoT) projects. Each level of fan duty lasted 3 hours.
Three used AQBlue masked were tested in used conditions, and washed by tap water, hang dry before testing again. The one with Airphin was tested with new, washed, and second washed.