Table 2.

Detailed information of the PFRs used by the participants in the included studies.

Study	Types of PFRs used by participants (did the used PFR had an exhalation valve?)	Time use of the PFRs by the participants in each intervention period	Have the efficiency/ penetration of PFRs been measured by the included studies?	Have the participants been instructed to wear PFRs accurately for ensuring a perfect fit with their face to minimize the penetration of PM through the gaps between the face and the PFRs?	Have the fit testing of PFRs been measured in the studies?	Were the participants ask to complete symptom questionnaire or data collection form on the respiration resistance, headache, difficulty in breathing when using the PFRs, comfortability/ intolerability of PFRs or other symptoms? If yes, what were their responses?
Han et al. (2021a)	N95 (8210 N95 Respirator, 3M Science, MN, United States) without exhalation valve	2 h	No (They reported that “ The N95 mask we used in this study was bought online, with the filtration efficiency on particles no less than 95%”).	No	No	No
Faridi et al. (2021)	Biomask (without exhalation valve)	The PFR intervention group was asked to wear their PFRs at all times while awake as much as possible when in the dormitory and when they were outdoors. The participants have reported that they wore the PFR between 10.2 and 11.1 h while awake during the interventions.	Yes (The efficiency of PFR used by the participants has been measured based on experimental set-up developed by the study against ambient PM1, PM2.5 and PM10 in a traffic-affected urban site in Tehran). The average filtering effectiveness of the used PFR was 83.5%, 68.1%, 46.1% and 32.2% in terms of ambient particle number concentration, PM10, PM2.5 and PM1 mass concentrations, respectively. This PFR reduced exposure to ambient PM10 in the range of 51.7–100.3 μg m−3, with a mean value of 94.6 μg m−3. The PFR reduced ambient PM2.5 and PM1 by 25.7–43.5 μg m−3 and 14.7–21.8 μg m−3, with mean values of 29.0 and 18.2 μg m−3, respectively.	Yes	No	Yes (More than 80% of participants reported increased respiratory resistance while wearing the PFR due to a lack of an exhalation valve. Of 26 participants, 22 and 23 subjects reported very high to moderate respiratory resistance and difficulty in breathing when using the PFR. In addition, 23 of participants stated that the PFR was very high to moderate intolerable due to its rigid ear loop clamps. Nine college students also reported very high to moderate headache while wearing the PFR.
Lim et al. (2020)	Disposable particulate respirators (PNTD, Mungyeong, Korea) (There is no information on whether PFR had the exhalation valve in the article.)	The participants wore PFRs for six consecutive days (excluding time spent eating, sleeping, and bathing).	No (They reported that “These particulate respirators are capable of filtering more than 80% of 0.6 μm nonoil particulates, meeting the Korea Food and Drug Administration KF80 standards”)).	Yes	Yes (Mask Fitting Tester MT-03 (SIBATA Science Technology, Saitama, Japan) was used. Out of 21 participants, only 14.3% (n = 3), 19% (n = 4) and 29% (n = 6) of participants showed less than 50% of leaking rate or passed each fitting test in the first, second and third leak tests.	No (One participant reported that she did not wear the PFR one morning while heading to the health examination for the experimental period. Another subject reported that she could not wear the respirator all the time because of intolerance to wearing the particulate respirator at home.)
Morishita et al. (2019)	N95 respirator (a new Dettol SiTi shield Protect Plus Smart Mask) with a micro- fan to lessen the buildup of heat, moister, and CO2 inside the respirator in the breathing zone	2 h	No (It has been reported that the PFR used by the participants validated and approved by the National Institutes of Occupational Safety and health (NIOSH)).	Yes	No	No
Yang et al. (2018b)	3M respirator (9002V), the used PFR had an exhalation valve.	4 h	No	Yes	Yes (Before the study, PFRs fit tests were conducted by using the TSI PortaCount Pro+8038 (TSI Inc., USA)), in accordance with the Occupational Safety and Health Administration (OSHA). The participants with the integrated fit factor >100 were included to participate in the study.	No
Shi et al. (2017)	Disposable particulate respirators (8210V; 3M™), the used PFR had an exhalation valve.	The participants were equally randomized into two groups and wore particulate- filtering respirators for 48 h The intervention group was required to wear their PFRs for all the time they were outdoors and as much as possible when they were indoors. It has been reported that the participants wore their respirators for more than 90% of their time outdoors and 82% of their time indoors, on average.	No (It has been reported that the PFR used by the participants validated and approved by the National Institutes of Occupational Safety and health (NIOSH)).	Yes	Yes (Before the intervention study, qualitative respirator fit testing on the face-to- respirator seal was performed using the 3M™ Qualitative Fit Test Apparatus FT-30 (3M™, USA). Additionally, the subjects positioned the respirators and then placed the professional testing hood on their heads. A bitter-tasting agent was sprayed into the hood. If the subject did not taste the bitter agent at all, the respirators were worn correctly. No detection of bitter taste in any test was considered as formally accepted.	Yes (The scores reported by the participants for the comfortability of respirators during the study period was 5 on average (on a scale from 0 to 10 referring to the worst comfort to the best)).
Langrish et al. (2012)	Dust Respirator 8812; 3M, St. Paul, MN, USA The used PFR had an exhalation valve.	Subjects were asked to wear the PFRs for 24 h before the PFRs study day, in addition to wearing it during the 24 h study day, and were given instructions to wear the PFRs at all times while outdoors and as much as possible when indoors.	No (It has been reported that the PFR used by the participants validated and approved by the EN149:2001 FFP1 European Standard (British Standards Institute, 2001)).	Yes	No	Yes (All subjects have stated that they tolerated the PFR intervention well, scoring the comfort of the PFR as 0.64 ± 1.06 on a 0–10 scale (0 represents completely comfortable, and 10, intolerable)).
Langrish et al. (2009b)	Dust Respirator 8812; 3M, St. Paul, MN, USA The used PFR had an exhalation valve.	When randomized to wear the PFRs, subjects were asked to wear the PFRs for 24 h prior to the study day and 24 h of the study day. Subjects were asked to wear the PFRs at all times when outside, and as much as possible whilst indoors.	Yes (It has been reported that the penetration of PFR has been measured using an experimental set-up against fresh diesel exhaust particulate (a mass concentration of 75 ± 12 μg m−3 (as measured by gravimetric analysis) and a particle number concentration equal to 500,000 particles/cm3)). The penetration for the used PFR was approximately 3.5%.	Yes	No	Yes (The participants have reported that the PFR was generally well tolerated with an average score of 24.8% (95% CI, 16.2–33.3%); 0% being completely tolerable and 100% being intolerable). Additionally, the subjects did report slightly greater difficulty breathing (increased resistance to respiration) whilst walking although this did not reduce the level of exercise undertaken by the subjects.