Effectiveness of Inexpensive Cloth Facemasks and Their Amendments to Reduce Ambient Particulate Exposures: A Case of Kathmandu, Nepal

Inexpensive cloth masks are widely used to reduce particulate exposures, but their use became ubiquitous after the outbreak of COVID-19. A custom experimental setup (semiactive at 5.1 m/s airflow rate) was fabricated to examine the efficiency of different types of commercial facemasks collected randomly from street vendors. The sample (N = 27) including (n = 16) cloth masks (CMs), (n = 7) surgical masks (SMs), and (n = 4) N95 filtering facepiece respirators (FFRs), of which SMs and N95 FFRs taken as a standard for efficiency comparison were all tested against ambient aerosols (PM2.5 and PM10 μg/m3). The prototype cloth masks (PTCMs) (N = 5) design was tailored, and their performance was assessed and compared with that of standard commercial masks. The filtering efficiency tested against ambient coarse particulates (PM10) ranged from (5% to 34%) for CMs with an average of 16%, (37% to 46%) for SMs with an average of 42%, (59% to 72%) for PTCMs with an average of 65%, and (70% to 75%) for N95 FFRs with an average of 71%, whereas against fine particulates (PM2.5), efficacy ranged from (4% to 29%) for CMs with an average of 13%, (34% to 44%) for SMs with an average of 39%, (53% to 68%) for PTCMs with an average of 60%, and (68% to 73%) for N95 FFRs with an average of 70%, respectively. The efficiency followed the order N95 FFRs > PTCMs > SMs > CMs showing poor exposure reduction potential in CMs and high exposure reduction potential in N95 FFRs and PTCMs. Amendment in existing CMs using eco-friendly cotton fabric with better facial adherence can protect human health from exposure to fine particulates <2.5 μm and can reduce the risk of micro-plastic pollution caused by polypropylene (PP) facemasks.


Introduction
Te bowl-shaped topographic structure in Kathmandu Valley is surrounded by mountains that are impediments to wind movement that retains particulates in ambient air [1,2], which is a key indicator of air pollution [3]. Trafcrelated particulate matter (PM) is considered a major contributor to overall ambient air pollution in Nepal [4,5], causing adverse impacts on the health of commuters and pedestrians due to their proximity to vehicular emissions [6,7] and also being responsible for an alteration of climate and visibility [8]. Particulate matter (PM) exposure is associated with respiratory and cardiovascular health efects [9][10][11] along with premature mortality [12,13], which refects global health concerns [14,15]. In Nepal, 24,000 premature annual deaths are expected to happen by 2030 due to ambient air pollution [16].
Long-term policies such as shifting to clean energy and short-term policies such as population-level interventions such as the use of respiratory protective devices (RPDs) might be the two efective approaches to reduce particulate exposures and other harmful airborne contaminants [5,17,18]. Application of RPDs has played a signifcant role as a frst-hand transmission controlling agent throughout history such as in the cases of acute respiratory syndrome coronavirus-1 (SARS-CoV-1) in 2003 [19], infuenza H191 in 2009 [20], avian H5N1 in 2003 [21], Ebola virus in 2014 [22], and Middle East respiratory syndrome coronavirus (MERS-CoV) in 2012 [23], respectively. Te surge in the use of facemasks took place after the outbreak of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) also known as COVID-19 from China [24,25] and was recognized as a pandemic by the WHO on 11 March, 2020 [26,27]. Facemasks were the only precaution taken during the COVID-19 pandemic [28][29][30] due to the limited supply of vaccines to meet global demand [31], resulting in global shortages of commercial facemasks and personal protective equipment (PPE) for healthcare workers (HCWs) [32][33][34].
Anecdotal evidence showed that during the Manchurian epidemic, handmade masks of cotton gauze became useful for military barracks and healthcare workers when quality commercial masks were inaccessible [35,36]. Simple, locally made, washable cloth masks (CMs) are suggested for use as an alternative when deprived of commercial masks [37,38]. Te researchers advocated for the public's use of CMs as a complementary countermeasure to the current COVID-19 pandemic [39][40][41] and they are being embraced worldwide [42]. Although limited scientifc data existing on the efcacy of CMs [43], people are using them because they are reusable and cheaper than surgical masks (SMs) and N95 fltering facepiece respirators (FFRs) [44,45]. Te efcacy of commercial facemasks certifed to local or international standards such as N95 FFRs and SMs are considered superior compared to that of CMs [28,46,47], but in some cases, their performance may not meet the exposure reduction potential that is marketed commercially [48]. Te efciency of facemasks against aerosols (viral or pollution particles) varies due to the diferent sizes, shapes, and properties of the particles [17]. Te efciency of facemasks is also afected by factors such as the charge of the aerosol, types of mask material, pollutant concentration, airfow rate, size and shape of the human face, facial hair, and way of wearing [48][49][50].
Very few studies have been done in Nepal regarding evaluating the efcacy of facemasks. Te study carried out by Shakya et al. [43] evaluated three CMs and one SM, and Neupane et al. [5] evaluated twenty CMs and seven SMs, which resulted in the efcacy of CMs being inferior. However, their study lacks providing insights regarding the improvement in CMs whose performance can be equivalent to that of standard commercial masks. Tis study gives an overview of the efcacy of CMs and the efcacy of their amended version known as prototype cloth masks (PTCMs) in this study as well as makes a comparison with the efcacy of SMs and N95 FFRs, which are taken as standards in this study. Te motivation for developing PTCMs in this study is to encourage people to use eco-friendly cotton facemasks with a better facial ft that have similar exposure reduction potential as polymer-based standard commercial facemasks that are a source of microplastic pollution.

Materials and Methods
Tis experiment was conducted in 2020 from February to March and August to November, consecutively, at the open ground of North Valley School, Kathmandu. As humans are naturally exposed to the ambient atmosphere, the experiment was conducted by extracting natural ambient aerosols in sealed setups ( Figure 1).
Tis experimental setup was fabricated using a normal plyboard, polyvinyl chloride (PVC) pipe, computer fan, revolutions per minute (RPM) controller, and a 12 V (volt) direct current (DC) charger. Ambient fne particulates (PM 2.5 ) and coarse particulates (PM 10 ) in real-time concentration (μg/m 3 ) were extracted at 5.1 m/s (stagnant air fow rate) and tested with two calibrated portable hand-held detectors (BR-Smart series model with an inbuilt light scattering measurement method, resolution: 1 μg/m 3 , and accuracy: ±10) simultaneously between fltrate air (with facemask) and nonfltrate air (without a facemask).
where "no mask" is the particles measured without wearing a mask, and "with mask" is the particles measured while wearing a mask on a human mannequin head.

Stitching of Prototype Cloth Masks (PTCMs).
Five different designs of cloth masks were conceptualized and stitched with the collaboration of a local garment factory in Kathmandu, Nepal (Table 1). Te PTCMs were stitched using a few varieties of cotton fabrics in all fve designs with the addition of a few accessories such as adjustable ear straps and nose pin for better facial adherence, pockets for inserting flters made of either polypropylene (PP) fabric or tissue paper as per the user's convenience.

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Journal of Environmental and Public Health Te average fltering efcacy of SMs against ambient PM 2.5 was found to be 39%. Te fltering efcacy of tested CMs against PM 10 ranged from 5% to 34%, with the lowest efcacy found on CM13 (5%) and the highest efcacy found on CM14 (34%) ( Table 4). Te highest fltering efciency in CM 14 was found to reduce PM 10 concentration from 61.48 ± 5.79 μg/m 3 to 40.3 ± 8.47 μg/m 3 with a total inward leakage (TIL) of 66%. Te average fltering efcacy of CMs against ambient PM 10 was found to be 16%.     Te fltering efcacy of tested cloth masks against PM 2.5 ranged from 4% to 29% with the lowest efcacy found on CM 13 (4%) and the highest efcacy found on CM 14 (29%) ( Table 5). Te highest fltering efciency in CM 14 was found to reduce PM 2.5 concentration from 49.64 ± 5.75 μg/m 3 to 35.15 ± 5.58 μg/m 3 with a total inward leakage (TIL) of 71%. Te average fltering efcacy of CMs against ambient PM 2.5 was found to be 13%.
Te more was efciency found the lesser the total inward leakage (TIL) for particulate fltration at the stated airfow rate. Te efciency followed the order N95 FFRs > PTCMs > SMs > CMs showing poor exposure reduction potential in CMs and high exposure reduction potential in N95 FFRs and PTCMs.
One-way analysis of variance (ANOVA) test showed that the efciency of all face masks against PM 10 and PM 2.5 are found to be signifcantly diferent from each other (p < 0.01), which rejected the null hypothesis of this study.

Discussion
Te efcacy of nasopharyngeal masks was estimated using diferent methods and techniques in previous studies, which contradict each other because diferent studies used diferent methods and experimental approaches whose fndings varied from study to study although studied for the same subject [7]. Te applied nasopharyngeal masks were found slightly better in efciency for ambient PM 10 aerosols than PM 2.5 due to the size and shapes of the aerosols [17]. Poor facial ft increases the particulate penetration level known as total inward leakage (TIL) [48,52] at diferent breathing frequencies [50] and particle penetration level decreases with increasing particle size [53,54]. Te TIL values were found to be low in SMs and N95 FFRs compared to CMs in our study and previous studies [55,56]. It is found that the efcacy of CMs widely varied from each other due to large pore size in CMs allowing particulates to pass easily, however, it performed well for larger particles >300 nm [42] and is believed to impede droplets and aerosols transmission [57]. Te fltering efciency of CMs ranging from 5% to 34% in our study has a close agreement with the efcacy range of 5% to 25% [58], 7% to 66% [48], 5% to 57% [43], and 34% to 66% [59], respectively. Te variation in efcacy can be attributed to the factors such as facial adherence, fabric material, airfow rate [48][49][50]60], and the sizes, shapes, and properties of aerosols [17].
Te efcacy of SMs was found better than that of CMs because it has similar surface characteristics as N95 FFRs embedded with a complex network of polypropylene (PP) nanofbers forming web-like structures interconnected with each other [5] and is triboelectrically charged to enhance the fltering efcacy by 6% to more than 10% [58]. However, its performance can decline in high airfow rate conditions due to its poor facial adherence (a gap between the nasal bone and face) [48,52], but can be improved if modifed with a better facial ft [61]. N95 FFRs, characterized by a complex network of multiple layers of nanofbers forming a web-like structure, melt-blown flters, and better facial adherence over the face [37,47,62] stand superior in reducing particulate exposures in our studies as well as in the previous study [46,63,64] that showed it is more capable of preventing nanoparticles from penetrating through its fabrics [65]. Te efcacy of N95 FFRs for coarse particulate matter ranging from 70% to 75% in our study has a close agreement with the efcacy range of 3.5% to 68.1% [46], whereas for fne particulate matter ranging from 68% to 73% in our study has a close agreement with the efcacy range of 14% to 96% [6].
Te fltering efcacy of PTCMs against fne particulates ranging from 53% to 68% in our study has a close agreement with the fltering efcacy ranged from 20% to 60% against fne NaCl particles [28]. Te average fltering efciency of PTCMs against fne particulates 60% in our study, which is in close agreement with the 45% average efcacy of layered fabrics [66]. Te stacking of diferent fabric layers in PTCMs played a signifcant role in reducing incoming particulates through fabrics in our study, as suggested by the study, of Drewnick et al., Zangmeister et al., and O'Kelly et al. [66][67][68]. Te better fltering efciency shown by N95 FFRs and SMs against various sizes of particulate matter [28,46,69] are sources of plastic pollution [70][71][72] because they are polymer products [73,74]. Such PP facemasks harm the environment, human health, and aquatic life and can jeopardize global food safety [75][76][77]. N95 FFRs are costly and cannot be reused multiple times. Te PTCMs in this study are made of cotton fabrics and are purely eco-friendly.
Tese modifed reusable CMs featured adjustable ear loops, pockets for installing replaceable flters, a nose pin for better facial ft, and some fabric layers for better fltration of particulate exposures, resulting in an efcacy almost

Conclusions
Te fltering performance of CMs was found to have poor exposure reduction potential and is marginally benefcial to human health compared to SMs and N95 FFRs. However, few amendments in inexpensive cloth mask materials and design that fts replaceable flters inside, whether PP flter or tissue paper as per that user's convenience, with the installation of a few accessories like a nose pin and adjustable ear straps for better adherence to the human face resulted in efcacy almost equivalent to standard N95 FFRs. Te fndings suggest that PTCMs can be potential alternatives to expensive standard masks and can play a pivotal role in reducing harmful ambient particulate exposures. Te fndings of this study can be helpful for the government to formulate policies and guidelines for better use of eco-friendly facemasks as well as it can also help the public regarding the proper selection of facemasks. Eco-friendly facemasks with better efcacy should be brought into mass production to replace plasticbased facemasks to protect both the environment and human health.

Limitations.
In the semiactive measurement experiment setup (Figure 1), the air inlet was maintained at 5.1 m/s, but an air outlet was not made, as well as the setups were not fully sealed, on the other hand the facemask sample testing zone was such that it stretched the fabric in some extent, which these all conditions favors the leakage of incoming PM particulates from both the fabric and the experimental setups. Te leakage source other than from fabric which acted as a confounding factor in this experiment was not measured. Because of these conditions, the efciency values were underestimated even for standard N95. More detailed studies are required to justify confounding factors that infuence the efcacy of facemasks.

Data Availability
Te data used to support the fndings of this study are available from the corresponding author upon request.

Ethical Approval
Tis study follows the ethical norms of scientifc research study and has been acknowledged by college research board members.

Disclosure
Tis study is a part of the M. Sc. dissertation completed by Mr. Prasidha Raj Neupane which is approved by the college research committee board. Tis study does not include any illicit experiment related to humans or any objects whatsoever.

Conflicts of Interest
Te authors declare that they have no conficts of interest.

Authors' Contributions
Mr. Prasidha Raj Neupane carried out the experiment, prepared the draft manuscript, and performed the data curation. Dr. Iswor Bajracharya conceptualized the research problem, devised the methodology, fabricated the experimental setup, supervised the entire research work, helped to draft the proposal for the research grant, and edited the draft manuscript. Mr. Sunil Babu Khatry helped during the experimentation, preparation of the draft, and checking of the language of the manuscript and experiment.