Effectiveness of Facemasks to Reduce Particulate Matter Exposure: A Case Study of Kathmandu Valley, Nepal

Abstract:

Facemasks are widely used to reduce airborne particle exposure as well as used extensively to avert the risk of current outbreak of novel Corona virus (COVID-19) disease, albeit limited scientific data on the efficacy of facemask exists. In this study, a custom experimental set-ups (sealed condition at the airflow rate of 150L/min and mannequin head to mimicry real human at the airflow rate of 50L/min) was fabricated to examine the efficiency of twenty-nine types of facemasks (eighteen types of cloth masks (CMs), seven types of surgical masks (SMs), three types of standard N95 masks, and one type of NIOSH N95 Respirator) samples collected from street vendors. This experiment was conducted extracting ambient aerosol comprising particulate matter of 2.5 μm or less (PM_2.5) and 10 μm or less (PM₁₀) measured in concentration (μg/m³) with the calibrated portable hand-held detector consecutively. A digital microscope (0.3m CMOS image sensor) was used to image and measure the pore size of all samples in the field of view (FOV) of 4.5 mm². From the sealed condition set-up, efficiency for PM_2.5 ranges from 67-72% in SMs, 45-73% in CMs, 75-78% in N95 facemasks, and 80% in NIOSH N95 respirator whereas efficiency for PM₁₀ ranges from 79-83% in SMs, 58-85% in CMs, 86-89% in N95 facemasks, and 91% in NIOSH N95 respirator respectively. Similarly from the mannequin head set-up, efficiency for PM_2.5 ranges from 33-49% in SMs, 14-59% in CMs, 60-63% in N95 facemasks, and 65% in NIOSH N95 respirator whereas efficiency for PM₁₀ ranges from 42-59% in SMs, 23-68% in CMs, 70-75% in N95 facemasks, and 75% in NIOSH N95 respirator respectively. Negative significant correlation (r = -0.80, p < 0.05) in sealed and (r = -0.94, p < 0.05) in mannequin head experimental set-ups were found between efficiency and pore size of facemasks. Positive significant correlation (r = 0.50, p <0.05) in sealed and (r = 0.68, p <0.05) in mannequin head experimental set-ups were found between efficiency and costs of facemasks. For PM_2.5 and PM₁₀ under investigation, unambiguously the best performance was found in N95 facemasks from both experimental set-ups, CMs found to have poor exposure reduction potential and are marginally beneficial in protecting human health from particles of 2.5 μm compared to SMs which are more effective in reducing particulate exposure.