Rapid review: Evaluating the effectiveness of masks and respirators against wildfire smoke

Executive Summary

Background

Short- and long-term exposure to gaseous and particulate matter (PM) air pollution is associated with a broad range of acute and chronic health outcomes across the life course. Air pollution can affect all organ systems in the body, inducing inflammation and oxidative stress. Most studies examining the health impacts of air pollution exposures have focused on air pollution generated in urban environments by traffic or industrial processes. However, large-scale fires (e.g., landscape and wildland-urban interface fires) can cause local, regional and widespread episodes of poor air quality. Such events are becoming more frequent and intense under climate change, leading to periods where large populations can be exposed to the resulting pollutants for days, weeks or months. As one of many strategies to reduce personal exposures to PM from wildfire smoke, Health Canada currently recommends wearing disposable respirators (e.g., N95). The aim of this rapid review is to assess the effectiveness of masks or respirators in reducing non-occupational exposures to gaseous and PM pollutants, specifically during combustion-derived air pollution episodes, including those caused by wildfires.

Research Questions

This rapid review seeks to identify, appraise and summarize available scientific research to support evidence-informed decision making in public health.

This rapid review includes evidence available up to April 23, 2025, to answer the questions:

1. What effect does wearing a mask or respirator have on reducing exposure to combustion-derived air pollutants?
    
2. What effect does wearing a mask or respirator during combustion-derived air pollution episodes have on human health endpoints?

This rapid review was produced through a collaboration between the National Collaborating Centre for Environmental Health (NCCEH) and the National Collaborating Centre for Methods and Tools (NCCMT).

Definitions

Mask: Unless specified, refers to a covering worn over the mouth and nose made of natural or synthetic materials. This includes both natural and synthetic cloth masks and surgical and procedural medical masks.

Respirator: Refers to a well-fitting disposable respirator or filtering facepiece respirator (e.g., N95, KN95, FFP, R95, P95, etc.). This term does not include elastomeric half- or full-face respirators that use disposable cartridges or powered air-purifying or supplied-air respirators.

Combustion-derived air pollution episode: Refers to unusual episodes of air pollution caused by combustion events such as wildland fires, coal mine fires, interface fires, agricultural fires, prescribed burns, industrial fires, landfill fires, tire fires, multi-day structural fires or urban conflagration, and residential wood combustion. This definition does not include air pollution generated from the combustion of fossil fuels (e.g., traffic-related air pollution (TRAP) or industrial processes).

Wildfire air pollution episode: Refers to unusual episodes of air pollution caused by combustion events such as wildland, forest, peat fires, interface fires, landscape fires, agricultural fires and prescribed burns.

Key Points

Overall

• The effectiveness of masks and respirators in mitigating non-combustion-derived exposures is well-supported by existing literature and has previously been systematically reviewed in previous reports. A summary of several key considerations and findings related to the performance of masks and respirators has been included to provide context for the results specific to combustion-derived air pollution episodes presented in this rapid review (see page 6).
• The evidence on the effect of wearing a mask or respirator on pollutant exposure and human health endpoints during combustion-derived air pollution episodes is limited. This review identified three studies that examined the effect of masks and/or respirators on reducing concentrations of combustion-derived air pollutants. No studies were found that examined the effect of wearing a mask or respirator on health endpoints during combustion-derived air pollution episodes.
• This rapid review used the Grading of Recommendations, Assessment, Development and Evaluation (GRADE) approach to assess the quality of the evidence with respect to specific effect estimates. Based on factors that affect the quality of evidence (e.g., limitations in study designs), the GRADE rating reflects how likely the reported effect estimate is to match the true effect.

Concentration reduction of Combustion-Derived Pollutants

• N95 respirators are effective at filtering PM derived from wood, paper and plastic combustion; the certainty of evidence, specifically with respect to the magnitude of the effect, is moderate (GRADE). Three quasi-experimental chamber studies reported > 94 per cent reduction in total PM ranging from 0.02 to 0.9 µm in diameter (PM_02-0.9) at a range of flow rates (15 to 85 L/min) simulating typical respiratory workloads. Only one study focused specifically on wood combustion, reporting a 97.7 per cent reduction in PM ranging from 0.02 to 0.9 µm in diameter. Another study examining Douglas fir pine needle combustion reported a 98.6 per cent reduction in PM ranging from 0.1 to 15 µm in diameter. All three studies used perfect-fit laboratory apparatuses that negate any leakage around the edges of the mask.
• R95 and P95 (oil-resistant and oil-proof) respirators may be effective at filtering PM from wood, paper and plastic combustion (> 99 per cent reduction in PM_02-0.9) at a high flow rate (85 L/min) that simulates strenuous respiratory workloads. The certainty of evidence, specifically with respect to the magnitude of the effect, is low (GRADE) due to high risk of bias stemming from limitations in study design and lack of corroborating studies.
• One quasi-experimental study reported that surgical masks may be effective at filtering PM from pine needle combustion (> 81 per cent reduction in PM_1-15) at a flow rate of 2.94 L/min (equivalent to a respiration rate of 41 L/min). The certainty of evidence, specifically with respect to the magnitude of the effect, is low (GRADE) due to high risk of bias stemming from limitations in study design and lack of corroborating studies.
• One quasi-experimental study reported that surgical masks and N95 respirators may be effective at reducing concentrations of pine needle combustion gases. This included volatile organic compounds (VOCs) such as acrolein (no mask: 250.6 ± 38.8 ppm, surgical mask: 129.1 ± 8.0 ppm, N95: 142.5 ± 10.3 ppm), and formaldehyde (no mask: 55.4 ± 5.8 ppm, surgical mask: 3.4 ± 0.5 ppm, N95: not detectable. The certainty of evidence, specifically with respect to the magnitude of the effect, is very low (GRADE) due to high risk of bias stemming from limitations in study design, lack of statistical analysis and lack of corroborating studies.

Human Health Endpoints

• No studies meeting the inclusion criteria for this rapid review were identified.

Overview of Evidence and Knowledge Gaps

Concentration reduction of Combustion-Derived Pollutants

• This rapid review includes three high-quality quasi-experimental studies.
• In two studies, N95 filtration rates were lower for PM from combustion of plastic (94.7 and 96.5 per cent reduction in PM_02-0.9) compared with wood (97.7 per cent) or test aerosols (e.g., NaCl, 98 per cent). This suggests that N95 filtration rates may be marginally lower during combustion-derived air pollution episodes involving synthetic materials (e.g., as derived from burnt structures during interface fires).
• In one study, penetration of N95 respirators by PM from plastic combustion increased significantly (p<0.05) when ambient relative humidity increased from 20 to 80 per cent (5.27 to 6.56 per cent in PM_02-0.9). This suggests that N95 respirators may be more effective in low-humidity environments for some pollutants. Furthermore, breathing adds humidity to air, and exhaled air saturated with water vapor may impact N95 respirator performance.
• In two studies, N95 respirator penetration was predominantly observed in the ultrafine range (particles < 0.1 µm in diameter), and in one study, 0.046 µm was reported to be the most penetrating wood combustion particle size. US National Institute for Occupational Safety and Health (NIOSH) standards for N95-type respirators are > 95 per cent filtration of test aerosol (i.e., NaCl) particles 0.3 µm in diameter. Because wildfire-related particle number and mass concentration size distributions are predominantly in the ultrafine range, and N95 respirators are less effective for ultrafine particles (Adhikari et al. 2018), the NIOSH rating may overestimate the effectiveness of respirators for combustion-derived pollution episodes (Sakamoto et al. 2015; Sparks & Wagner 2021).
• One study compared the effectiveness of a cloth mask (single-layer cotton bandana), a surgical mask, and an N95 respirator for blocking particles from Douglas fir pine needle combustion. This study reported statistically significant PM_1-15 filtration for the surgical mask (81.3 ± 5.1 per cent) and N95 respirator (98.6 ± 0.4 per cent), but not for the cloth mask (8.9 ± 1.7 per cent). The study did not account for any differences in bypass rates.
• One study compared the effectiveness of a cloth mask, a surgical mask and an N95 respirator at reducing Douglas fir pine needle combustion gases. Reductions (no statistical analysis reported) were observed for known respiratory irritants including acrolein and formaldehyde in the surgical mask and N95 respirator conditions, but not the bandana. However, the short duration of the test (15 minutes) may not accurately represent the filtering or blocking effectiveness of these masks on combustion gases, because the loading rates and capacities of the materials may be exceeded over longer durations.
• There is limited research on how the physiochemical properties of combustion-derived particles (e.g., hydrophobicity) may alter mask efficiency (e.g., degrade or chemically modify the filter material). One study hypothesized that combustion particles may degrade N95 respirators when depositing on filter fibres due to the presence of hydrophobic organic compounds and/or reduce the charge on electrostatic filter material from charged particle deposition. This study examined the effectiveness of R95 and P95 respirators (oil-resistant and oil-proof), based on their design to filter hydrophobic particles, and observed increased PM filtration compared with N95 respirators (> 99 per cent vs. > 96 per cent PM_02-0.9 reduction, no statistical analysis reported). This small increase may not be relevant in the context of public health.
• There were no studies that examined the effectiveness of masks and/or respirators in a typical use setting (e.g., accounting for realistic bypass rates and user compliance). All three studies used methods that provided a perfect mask or respirator fit or seal in a model system, simulating a best-possible use scenario. For example, it has been reported that poorly fitted respirators can decrease the effectiveness of particle filtration to 60 per cent in the context of manufacturing emissions (e.g., welding, casting, and asphalt production) (Mitra et al., 2021). Furthermore, surgical masks are known to have a higher particle bypass rate compared with N95 respirators in ideal fit conditions (Wang et al., 2023).

Human Health Endpoints

This rapid review identified no published, peer-reviewed research on the effects of wearing a mask or respirator during combustion-derived air pollution episodes on human health endpoints (e.g., any direct or indirect acute or long-term health outcome, use of emergency services or hospitalizations, and cellular-level outcomes). As a result, public health authorities must rely on indirect evidence of mask use in other contexts to inform decisions regarding their use during wildfires. Future research is needed to explore these effects among both the general population and those for whom social and structural inequities apply.

Introduction

Masks and respirators are known to be effective infection control devices and have been extensively reviewed elsewhere (O’Keeffe et al. 2021). In the context of non-biological exposures, current evidence suggests that masks and respirators can decrease acute exposure to air pollutants and related adverse health effects (Laumbach et al. 2022). However, evidence on their effectiveness in reducing non-occupational exposures to pollutants from events like wildfires remains less clear. This rapid review aims to fill this important knowledge gap and identify areas for further study. There is a relatively large body of evidence on the general effectiveness of masks and respirators, which is summarized below to provide context for the results reported in this rapid review specific to combustion-derived air pollution episodes. Select information on occupational wildfire exposures is also included.

Background

The term “mask” can refer to many different coverings worn over the mouth and nose that block the inhalation or release of particles in the air. These devices prevent inhalation of particles by removing them from air by interception, inertial impaction on a surface, electrostatic attraction, diffusion or other physical removal mechanisms. These devices can include non-medical masks (e.g., cloth), medical masks (e.g., surgical or procedure masks), and disposable respirators or filtering facepiece respirators (e.g., N95, KN95) (Health Canada 2024). Non-medical masks are often made from two to three layers of cloth that cover the nose and mouth. The degree of protection can vary widely for these masks depending on their material (e.g., synthetic or natural fibres) and fit, which can be defined by the mask itself (e.g., elastic ear loops, straps, nose bridge) or user-specific factors (e.g., facial hair, facial shape, behaviour). No performance standards for non-medical masks exist. Procedure or surgical masks also vary in construction and materials, but they must meet minimum standards for inward and outward particle and droplet filtration to be classified as medical masks. For instance, the ASTM F2100 Level 3 standard requires ≥ 98 per cent bacterial filtration efficiency and 0.1 micron particulate filtration efficiency (Health Canada 2021). Surgical and procedural masks are intended to block the passage of infectious material and bodily fluids, but are less effective at filtering airborne particles due to their loose fit (Lee et al. 2016). Disposable respirators, when fit tested, are certified to meet specific performance standards (e.g., NIOSH or CAN/CSA Z94.4-18) for filtering particles. For instance, a NIOSH-certified N95 respirator filters at least 95 per cent of particles with a 0.3-micron diameter.

Using a mask or respirator to reduce personal exposures is governed by several key factors that include filtration efficiency, bypass rate, and compliance rate (O’Keeffe et al. 2021). Filtration efficiency refers to the percentage of particles the mask material can block, whereas bypass rate refers to the quantity of particles that flow around mask edges. Compliance rate refers to the actual time worn in a polluted environment. When comparing the performance of masks and respirators, respirators are known to be more effective at blocking or filtering particles than non-medical cloth masks or surgical or procedural masks (Wang et al. 2023). Using a 0 per cent bypass rate model, one laboratory study comparing non-medical natural material mask, surgical mask and N95 respirator efficiency reported the percentage of test aerosol particles ranging from 0.01 to 10 µm in diameter blocked to be 21, 91, and 97 per cent, respectively (Kodros et al. 2021). When accounting for mask fit, surgical and N95 masks have protection factors, defined as NaCl test aerosol concentration out/in, ranging from 1.5 to 1.8 and 15.9 to 31.9, respectively, for particles in the 0.093 to 1.61 µm size range (Lee et al. 2016). For context, the median particle diameter in boreal wildfire smoke plumes was estimated to be between 0.059 and 0.094 µm (Sakamoto et al. 2015). Similar differences in protection between surgical masks and N95 respirators have been reported for surgical smoke with peak particle sizes between 0.06 and 0.15 µm diameter (Gao et al. 2016). For wildfire smoke particles specifically, a modelling study estimated mask collection efficiencies accounting for filtration efficiency and fit reported values of 0.33, 0.68 and 0.9 for cloth masks, surgical masks and respirators, respectively (Wagner et al. 2022).

Based on current evidence, public health authorities often recommend using well-fitted (e.g., fit-tested) disposable respirators (e.g., N95, KN95, FFP) to reduce personal exposures to air pollution, including wildlife smoke (Laumbach et al. 2022). A recent systematic review and meta-analysis of eight studies examining the impact of respirator use to reduce ambient air pollution exposure on markers of cardiorespiratory health found significant improvements ranging from 2.2 to 18.84 per cent in heart rate variability (Liu et al. 2022). Another systematic review and meta-analysis of eight studies and 312 participants found that reducing PM exposures via respirator use (2 to 48 h intervention periods) resulted in a significant reduction of mean arterial pressure (Faridi et al. 2022). Significant improvements in markers of systemic inflammation were also reported in participants wearing actual N95 respirators while walking for two hours along a busy traffic road compared with those wearing a sham respirator (Guan et al. 2018).

Although current evidence indicates that wearing an N95 respirator in a polluted environment can protect health, the effect of non-medical cloth masks or surgical or procedural masks is less clear. One modelling study using data from the 2012 Washington state wildfire season estimated that natural cloth masks, surgical masks or N95 respirators used at a 2/3 compliance rate would have reduced wildfire smoke-attributable respiratory hospitalizations by 2 to 11, 9 to 24, and 22 to 39 per cent, respectively. This study accounted for differences in bypass rates and filtration efficiency in the particle size range typical of wildfire smoke (Kodros et al. 2021). Another modelling study estimated 57,937 people in the United States would need to wear an N95 respirator over a two-week exposure to 200 µg/m³ PM_2.5 to prevent one atherosclerotic cardiovascular disease event (fatal or nonfatal myocardial infarction or stroke) assuming 75 per cent respirator efficiency to account for fit and compliance (Brook et al. 2024).

Several studies have also examined the effectiveness of wearing masks in occupational contexts, such as in protecting wildland firefighters. One study examining the use of fit-tested N95 respirators by 19 firefighters during the 2021 fire season in Alberta and British Columbia (BC) reported significantly fewer cough, nose and throat symptoms among respirator wearers compared with a control group (Cherry et al. 2022). Two other studies have examined the use of masks and respirators for protection against the harmful effects of polycyclic aromatic hydrocarbon (PAH, a component of woodsmoke) exposure as measured by urinary 1-Hydroxypyrene (1-HP) levels. When natural fibre cloth masks and mesh carbon filter masks were compared with a no mask condition, end of shift 1-HP was significantly lower only for those wearing carbon filter masks. These differences were only statistically significant on above-average PAH concentration days in mask-fit-tested and beardless BC firefighters (Broznitsky et al. 2024). In the second study on 86 firefighters from Alberta and BC, a non-significant decrease in end-of-shift 1-HP (post–pre) from 76.1 ± 101.3 to 27.0 ± 44.4 ng g⁻¹ creatinine (p=0.461) was observed when comparing those wearing with those not wearing an N95 respirator (Cherry et al. 2021).

In summary, current evidence suggests that masks and respirators can decrease exposure to air pollutants and related adverse health effects. Yet, in non-occupational exposures to pollutants from events like wildfires, the effectiveness of wearing a mask or respirator is less defined.

Methods

A description of the development of the NCCMT’s Rapid Evidence Service, including an overview of the rapid review process and rationale for methodological decisions, has been published (Neil-Sztramko et al. 2021).

Research Question

This rapid review addresses the following research question, developed in collaboration with public health decision makers:

1. What effect does wearing a mask or respirator have on reducing exposure to combustion-derived air pollutants?
    
2. What effect does wearing a mask or respirator during combustion-derived air pollution episodes have on human health endpoints?

The study protocol was registered in PROSPERO (CRD42024592977).

Search

Information specialists from the NCCEH and McMaster University were involved in developing and conducting the search.

On April 23, 2025, the following databases were searched using key terms, including: “wildfire,” “smoke,” “masks,” “respiratory protective devices”:

• MEDLINE
• Embase
• CINAHL
• Environment Complete

A special issue of Environmental Science & Technology – Emissions, Chemistry, and the Environmental Impacts of Wildland Fire – and four other journals, not indexed in the databases above, were hand searched for relevant studies. The reference lists of related systematic reviews were screened and subject matter experts in the field were consulted.

This search builds upon the previous search (November 21, 2024) conducted in the first version of this rapid review. A copy of the full search strategy is available in Appendix 1.

Study Selection Criteria     

This rapid review included a comprehensive search of the peer-reviewed literature and manual searches of relevant special issues. However, it did not include evidence from the grey literature. Subsequent review updates could consider expanded search strategies and inclusion criteria (e.g., unpublished, non-peer-reviewed sources).

The titles and abstracts of a proportion of results (10 per cent) were screened in duplicate to confirm reviewer agreement; disagreements were resolved through consensus or consulting with a third reviewer. The remaining results were screened by a single reviewer. The full texts of results included in title and abstract screening were retrieved and screened by a single reviewer. Continuous artificial intelligence (AI) reprioritization was used to sort results during both levels of screening, but all references were screened manually.

English-language, peer-reviewed sources were eligible for inclusion; sources published ahead of print, before peer review, and surveillance sources and mathematical modelling studies that exclusively used estimated data were excluded.

1. What effect does wearing a mask or respirator have on reducing exposure to combustion-derived air pollutants?

2. What effect does wearing a mask or respirator during combustion-derived air pollution episodes have on human health endpoints?

*Cellular-level outcomes, as indirect subclinical effects, were originally excluded; they were included after it became clear that the data on more direct health outcomes was limited.

Data Extraction and Synthesis

When reported in the included studies, data relevant to the research question, including study design, interventions and outcomes, were extracted by one reviewer and verified by a second.

The results were synthesized narratively due to the variation in methodology and outcomes for the included studies.

Appraisal of Evidence Quality and Certainty

The quality of included evidence was evaluated using critical appraisal tools, as indicated by the study design below. Quality assessment was completed in duplicate by two independent reviewers; conflicts were resolved through discussion or by a third reviewer.

Completed quality assessments for each included study are available on request.

The Grading of Recommendations, Assessment, Development and Evaluations (GRADE) (Schünemann et al. 2013) approach provides a framework for assessing health care questions and, importantly, clearly separates rating the confidence in an effect estimate of an intervention from rating the strength of a recommendation on using the intervention. It should be noted that strong recommendations can be formed from low quality evidence and vice versa. The GRADE approach was used to assess the certainty in the findings in quantitative research based on eight key domains. 

In the GRADE approach to quality of evidence, observational studies, as included in this review, provide low quality evidence, and this assessment can be further reduced based on:

• High risk of bias
• Inconsistency in effects
• Indirectness of interventions/outcomes
• Imprecision in effect estimate
• Publication bias

and can be upgraded based on:

• Large effect
• Dose-response relationship
• Accounting for confounding

The overall certainty in the evidence for each outcome was determined, considering the characteristics of the available evidence (observational studies, some not peer-reviewed, unaccounted-for potential confounding factors, different tests and testing protocols, lack of valid comparison groups). A judgement of “overall certainty is very low” means that the findings are very likely to change as more evidence accumulates.

In addition to considering the quality and certainty of the included evidence, the findings from this rapid review should be interpreted in the context of the methodological restrictions inherent in a rapid review process (Garritty et al. 2024). For example, limited database searching and single reviewer screening may result in missed studies.

Findings

Summary of Evidence

1. What effect does wearing a mask or respirator have on reducing exposure to combustion-derived air pollutants?

This rapid review included three single studies. The certainty of the key findings included in this review is as follows:

Abbreviations: PM_x-y: particulate matter ranging from x-y µm in diameter.

*Values exceed the total number of studies (n=3) as some studies contributed to multiple key findings.

¹In the GRADE approach to certainty of evidence, experimental studies, as included in this review, provide moderate certainty evidence; this was downgraded due to risk of bias due to limitations in study designs and then upgraded to moderate based on the consistent large magnitude of effect.

²In the GRADE approach to certainty of evidence, experimental studies, as included in this review, provide moderate certainty evidence; this was downgraded to low due to high risk of bias due to limitations in the study design.

³In the GRADE approach to certainty of evidence, experimental studies, as included in this review, provide moderate certainty evidence; this was downgraded to very low due to high risk of bias due to limitations in the study design.

2. What effect does wearing a mask or respirator during combustion-derived air pollution episodes have on human health endpoints?

This rapid review did not identify any studies that met the inclusion criteria for the above question.

Please see PDF for full results table.

References

Adhikar, A., Mitra, A., Rashidi, A., Ekpo, I., Schwartz, J., & Doehling, J. (2018). Field evaluation of N95 filtering facepiece respirators on construction jobsites for protection against airborne ultrafine particles. International Journal of Environmental Research and Public Health, 15(9), 1958.

Brook, R.D., Rajagopalan, S., & Al-Kindi, S. (2024). N95 respirators for cardiovascular protection during wildfire smoke events. Journal of the American Heart Association, 13(2), e032422.

Broznitsky, N., Shum, M., Kinniburgh, D., Lichty, D., Tiu, S., Toic, T., … Cherry, N. (2024). A field investigation of 3 masks proposed as respiratory protection for wildland firefighters: a randomized controlled trial in British Columbia, Canada. Ann Work Expo Health. 68(9):906-918.

Cherry, N., Galarneau, J-M., Kinniburgh, D., Quemerais, B., Tiu, S., & Zhang, X. (2021). Exposure and absorption of PAHs in wildland firefighters: A field study with pilot interventions. Annal of Work Exposures and Health, 65(2), 148-161.

Cherry, N., Broznitsky, N., Fedun, M., & Zadunayski, T. (2022). Respiratory tract and eye symptoms in wildland firefighters in two Canadian provinces: Impact of discretionary use of an N95 mask during successive rotations. International Journal of Environmental Research and Public Health, 19(20), 13658.

Faridi, S., Brook, R.D., Yousefian, F., Sadegh Hassanvand, M., Nabizadeh Nodehi, R., Shamsipour, M., … Naddafi, K. (2022). Effects of respirators to reduce fine particulate matter exposures on blood pressure and heart rate variability: A systematic review and meta-analysis. Environmental Pollution, 303, 119109.

Gao, S., Kim, J., Yermakov, M., Elmashae, Y., He, X., Reponen, T., & Grinshpun, S.A. (2015).  Penetration of combustion aerosol particles through filters of NIOSH-certified filtering facepiece respirators (FFRs). Journal of Occupational & Environmental Hygiene, 12(10), 678.

Gao, S., Kim, J., Yermakov, M., Elmashae, Y., He, X., Reponen, T., … Grinshpun, S.A. (2016).  Performance of N95 FFRs against combustion and NaCl Aerosols in dry and moderately humid air: Manikin-based study. Annals of Occupational Hygiene, 60(6), 748.

Gao, S., Koehler, R.H., Yermakov, M., & Grinshpun, S.A. (2016). Performance of facepiece respirators and surgical masks against surgical smoke: Simulated workplace protection factor study. The Annals of Occupational Hygiene, 60(5), 608–618.

Garg, P., Wang, S., Oakes, J.M., Bellini, C., & Gollner, M.J. (2023). The effectiveness of filter material for respiratory protection worn by wildland firefighters. Fire Safety Journal, 139, 103811.

Garritty, C., Hamel, C., Trivella, M., Gartlehner, G., Nussbaumer-Streit, B., Devane, D., … King, V.J. (2024). Updated recommendations for the Cochrane rapid review methods guidance for rapid reviews of effectiveness. BMJ, 384:e076335.

Guan, T., Hu, S., Han, Y., Wang, R., Zhu, Q., Hu, Y., … Zhu, T. (2018). The effects of facemasks on airway inflammation and endothelial dysfunction in healthy young adults: A double-blind, randomized, controlled crossover study. Particle and Fibre Toxicology, 15(30).

Health Canada. (2021). Guidance for transparent medical mask technical specifications: Technical requirements for manufacturers. Accessed May 22, 2025.

Health Canada. (2024). Masking: Types of masks. Accessed May 22, 2025.

Kodros, J.K., O’Dell, K., Samet, J.M., L’Orange, C., Pierce, J.R., & Volckens, J. (2021). Quantifying the health benefits of face masks and respirators to mitigate exposure to severe air pollution. GeoHealth, 5(9), e2021GH000482

Laumbach, R.J., & Cromar, K.R. (2022). Personal interventions to reduce exposure to outdoor air pollution. Annual Review of Public Health. 43, 293-309

Lee, S-A., Hwang, D-C., Li, H-Y., Tsai, C-F., Chen, C-W., & Chen, J-K. (2016). Particle size-selective assessment of protection of European standard FFP respirators and surgical masks against particles-tested with human subjects. Journal of Healthcare Engineering, 8572493.

Liu, S., Wu, R., Zhu, Y., Wang, T., Fang, J., Xie, Y., … Huang, W. (2022). The effect of using personal-level indoor air cleaners and respirators on biomarkers of cardiorespiratory health: A systematic review. Environment International, 158, 106981.

Mitra, A., Adhikari, A., Martin, C., Dardano, G., Wagemaker, P., & Adeoye, C. (2021). Evaluation of a filtering facepiece respirator and a pleated particulate respirator in filtering ultrafine particles and submicron particles in welding and asphalt plant work environments. International Journal of Environmental Research and Public Health, 18(12), 6437.

Neil-Sztramko, S.E., Belita, E., Traynor, R.L., Clark, E., Hagerman, L., & Dobbins, M. (2021). Methods to support evidence-informed decision-making in the midst of COVID-19: creation and evolution of a rapid review service from the National Collaborating Centre for Methods and Tools. BMC Medical Research Methodology, 21(231).

O’Keeffe, J. (2021) Masking during the COVID-19 pandemic - an update of the evidence. National Collaborating Centre for Environmental Health.

Sakamoto, K.M., Allan, J.D., Coe, H., Taylor, J.W., Duck, T.J., & Pierce, J.R. (2015). Aged boreal biomass-burning aerosol size distributions from BORTAS 2011. Atmospheric Chemistry and Physics, 15, 1633–1646.

Schünemann, H., Brożek, J., Guyatt, G., & Oxman, A. (2013). Handbook for grading the quality of evidence and the strength of recommendations using the GRADE approach.

Sparks, T.L., & Wagner, J. (2021). Composition of particulate matter during a wildfire smoke episode in an urban area. Aerosol Science and Technology, 55(6), 734-747.

Wagner, J., Macher, J.M., Chen, W. & Kumagai, K. (2022). Comparative mask protection against inhaling wildfire smoke, allergenic bioaerosols, and infectious particles. International Journal of Environmental Research and Public Health, 19(23), 15555.

Wang, A-B., Zhang, X., Gao, L-J., Zhang, T., Xu, H-J., & Bi, Y-J. (2023). A review of filtration performance of protective masks. International Journal of Environmental Research and Public Health, 20(3), 2346.

Appendix 1: Search Strategy

On April 23, 2025, the following four databases were searched using the search terms and parameters below.

A special issue of Environmental Science & Technology – Emissions, Chemistry, and the Environmental Impacts of Wildland Fire – and the following four journals were also hand searched, from 2004 (or journal’s inception) to current issue:

• Journal of Exposure Science & Environmental Epidemiology
  • Volumes 14 (2004) to 35 (2025)
• Current Pollution Reports
  • Volumes 1 (2015) to 11 (2025)
• Aerosol and Air Quality Research
  • Volumes 4 (2004) to 24 (2024)
• International Journal of Disaster Risk Reduction
  • Volumes 1 (2012) to 123 (2025)

The reference lists of related systematic reviews were screened and subject matter experts in the field were consulted.

This search builds upon the search conducted in the first version of this rapid review (date limit: January 1, 2004 to November 21, 2024). An archived copy of the previous search strategy is available.
 

MEDLINE

Embase

CINAHL

Environment Complete