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Article

Efficacy of Acid-Treated HEPA Filters for Dual Sequestration of Nicotine and Particulate Matter

by
Toluwanimi M. Oni
,
Changjie Cai
and
Evan L. Floyd
*
Department of Occupational and Environmental Health, Hudson College of Public Health, University of Oklahoma Health Sciences Center, Oklahoma City, OK 73104, USA
*
Author to whom correspondence should be addressed.
Air 2025, 3(1), 8; https://doi.org/10.3390/air3010008
Submission received: 18 October 2024 / Revised: 10 February 2025 / Accepted: 17 February 2025 / Published: 4 March 2025
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Abstract

:
Tobacco smoking and electronic cigarette (EC) use are associated with elevated levels of particulate matter (PM) and nicotine in indoor environments. This study assessed filtration and nicotine capture efficiency of untreated and citric acid-treated high efficiency particulate air (HEPA) filters from two manufacturers, “on-brand” (original) and “off-brand” (replacement). When challenged with salt aerosol, the filtration efficiency (FE) (Mean ± RSD) of original HEPA filters (99.9% ± 0.1) was significantly higher than replacements (94.4% ± 1.7), but both were significantly below the HEPA designation of 99.97%. No significant differences in FE were observed between treated and untreated HEPA filters. All filters had lower FE for EC aerosol compared to salt aerosol, especially among replacement filters. Nicotine capture efficiency was significantly higher in citric acid-treated HEPA filters for originals (99.4% ± 0.22) and replacements (99.0% ± 1.07) compared to untreated originals (57.4% ± 2.33) and replacements (42.0% ± 14.20). This study demonstrated that our citric acid treatment of HEPA filters was effective and efficient at capturing airborne nicotine and did not affect the FE for PM. Use of citric acid-treated HEPA filters would be an effective exposure reduction strategy for both nicotine and PM in indoor settings.

1. Introduction

Secondhand exposures to tobacco smoke and electronic cigarette (EC) aerosol may adversely impact vulnerable populations such as pregnant women, children, immune compromised and those with respiratory diseases. Many health problems such as respiratory illnesses [1,2,3,4,5], molecular and genetic damage in children [6], cardiovascular disease [7,8,9], cancer [10] and death [5,9,11] have been associated with secondhand tobacco smoke exposures [1,2,3,4,5,6,10]. Similarly, secondhand EC aerosol exposure has been linked to adverse fetal health [12], respiratory challenges among adolescents and young adults [13,14,15,16] and cardiovascular effects [17]. Secondhand tobacco smoke is a combination of smoke from burning tobacco products such as cigarettes or cigars and exhaled smoke [18] and consists of thousands of chemicals, many of which are toxic [18,19]. Secondhand electronic cigarette aerosols also contain toxins such as formaldehyde [20,21] and heavy metals [22,23,24]. Although elimination of indoor smoking and EC use is the ideal strategy for reducing secondhand exposures [25], there is need to develop and evaluate hazard control strategies to improve indoor air quality in environments with tobacco smoke and EC use.
Portable air purifiers (PAPs) with High Efficiency Particle Air (HEPA) filters have been commonly and effectively deployed for the removal of air pollutants in indoor environments [26,27,28,29]. HEPA is a technical term for an air filter capable of removing at least 99.97% of all particles in the air that pass through it [30,31,32,33] when used as intended. HEPA filters are designed to remove particulate matter, not gases and vapors. It is only through incidental absorption that gases and organic vapors are removed from the air by HEPA filters [34,35]. To increase their capacity and efficacy for organic vapors, often a layer of granular activated carbon is added after the HEPA filter element [35,36].
The application of PAPs equipped with HEPA filters to reduce EC emissions in indoor settings has been demonstrated [37] but that study only examined the impact of air purification on PM levels, not nicotine. The present study was aimed at modifying HEPA filters so that they can be efficient for the removal of both particles and nicotine vapor arising from tobacco smoke or EC emissions. We modified HEPA filters by treating them with an acid, similar to the analytical approach developed by Hammond et al. [38], and adapted by Oni et al. [39] for combination with real-time aerosol monitoring. A similar approach was previously explored by Aquilina et al. [40] for high volume ambient air sampling in an urban environment to determine source apportionment of urban particulates, with particular interest in tobacco smoke contribution.

2. Materials and Methods

2.1. Summary

In this study, filters were treated with an acid particulate through an aerosolization process instead of the wet treatment approach used by others [38,39,40]. This approach was selected for multiple reasons: (1) wetting a commercial HEPA filter might impact the structural cardboard components of the filter that are essential to providing good fit within the PAP; (2) wetting an electret filter can dissipate the charge on the fibers and may reduce the filtration efficiency; (3) wet filter fibers may clump together during drying due to the high surface tension of water; (4) the geometry of the HEPA filters are complex and ensuring an even acid loading, wetting and drying was uncertain; and (5) depositing acid as an aerosol would ensure the acid treatment is deposited in a similar manner as particles in the air.
This study compared particle filtration efficiency and nicotine capture efficiency of acid-treated and untreated HEPA filters using a salt aerosol, and nicotine-containing EC aerosol. We also compared two types of filters, those that were the same brand as the PAP and low-cost “off-brand” filters that were marketed as being compatible replacements and had packaging that clearly claimed HEPA filtration quality. All comparison tests were performed using four PAP units of the same make and model to account for practical differences in manufacturing and fit of HEPA filters within each PAP unit.

2.2. Materials

The PAP selected for this study was a Levoit Core 400S Smart Air Purifier. Four of these PAPs were used to conduct this study. The filters used in this study were Levoit Core 400S 3-Stage replacement filters (UPC: 810043372893), subsequently referred to as “original” HEPA filters and Kaulolado Core 400S replacement for Levoit (UPC: 738157595789), subsequently referred to as “replacement” HEPA filters. Both the original and replacement HEPA filters were 24.5 cm × 24.5 cm × 26.5 cm (Length × Width × Thickness) in dimensions and consisted of a preliminary filter, pleated main filter and activated carbon final layer. The only observable difference between the filter types was in the color of their foam gaskets for sealing airflow; with the originals being grey and the replacements being black (See Figure 1).
Each air purifier was assessed for flowrate with the different treated and untreated HEPA filter brands at the lowest fan setting using a balometer (TSI ALNOR Air Flow Capture Hood; model EBT731, TSI, Shoreview, MN, USA) with these values shown in Table 1. Replacement filters had small but significantly higher flowrates than the original filters (6.3% greater, p < 0.001). There was no difference in air flowrates due to treatment (original p = 0.263; replacement p = 0.890). Filter weight was also measured to investigate observed performance differences between the original and replacement filters. These masses are shown in Table 2. Replacement filters had significantly greater mass than original filters (p < 0.001), but there was no difference in filter mass due to treatment (original p = 0.613; replacement p = 0.060). The number of filter pleats were counted for 4 original and 4 replacement filters (Table 3). Replacement filters had significantly higher number of pleats compared to the original filters (p < 0.001).
Citric acid (USP grade, Aroma Depot) was used to treat the HEPA filters in this study. Citric acid was selected for use for two main reasons: (1) Oni et al. [39] observed that citric acid had ~7x the holding capacity of sodium bisulfate, the acid used in previous analytical applications [38,40]. This is likely because citric acid is a tri-protic, organic acid whereas sodium bisulfate is a mono-protic inorganic acid with minimal affinity for nicotine other than the acid-base interaction. (2) Oni et al. also observed low nicotine recovery rates from citric acid at low nicotine loading levels, indicating citric acid does not release nicotine even when neutralized and extracted with an organic solvent. Therefore, citric acid seemed to be more favorable for long-term, high capacity sequestration of nicotine from the air than sodium bisulfate.

2.3. Study Design

This study assessed the FE of two brands of filters (original and replacement) and treatment status of filters (untreated and citric acid treated). Reference FE was assessed using a salt aerosol instead of dispersed oil particulate (DOP) aerosols (EN 1822-1:2019 testing protocol for HEPA filters [41]). This was to avoid coating of the HEPA filters’ fibers with oil which may impact FE of the HEPA filters when evaluated against other challenge agents [42]. Real-world FE performance was assessed using EC aerosol. Nicotine capture efficiency was assessed using EC aerosol. Comparisons were made between original and replacement filters to determine if there was a difference between the HEPA filter brands. Comparisons were made between treated and untreated filters to test for the effect of citric acid treatment on HEPA filter FE. Comparisons were made between the four unique filter-treatment combinations to assess the effect of citric acid treatment on nicotine capture efficiency. For all experiments involving original filters there were four replicates (n = 4), for all experiments involving replacement filters there were eight replicates (n = 8).

2.4. HEPA Filter Treatment

A citric acid solution was aerosolized using an ultrasonic humidifier (HiLIFE HF4) operated at the highest setting, which we found to consume 300 mL/h. The citric acid droplets were drawn into a 1 m3 chamber, mixed with chamber air and draw through a HEPA filter installed in a PAP. Each PAP was operated at its lowest fan setting (see Table 1) and connected to an exhaust duct so that all air passing through the PAP was expelled from the chamber. This was to prevent humidity buildup in the chamber and ensure maximum evaporation of citric acid droplets before depositing on the HEPA filter. Each HEPA filter received a deposition of 10 g of citric acid on its surface, which was 3 times the amount required (3.26 g) to capture nicotine during EC aerosol challenge. Additionally, following the citric acid deposition, lab air was drawn through each citric acid-treated HEPA filter for an hour to ensure the filter was fully dry.

2.5. Filtration Efficiency and Nicotine Capture Efficiency Evaluation

The performance evaluation setup is illustrated in Figure 2. An air purifier was placed into the environmental chamber with its air exit connected to an exhaust duct. Both particulate matter (PM) and nicotine were measured within the chamber (upstream) and within the exhaust duct (downstream). PM was measured using GRIMM portable aerosol spectrometers (GRIMM, PAS 1.108, Durag Group, Hamburg, Germany). Nicotine was collected for measurement on 47 mm GF/A filters (Whatman, Grade GF/A, Cytiva, MA, USA) treated with sodium bisulfate, sampled at 2.0 L/min and analyzed by GCMS using the method described by Oni et al. [39].
Each HEPA filter was challenged with (1) salt aerosol to assess the filtration efficiency and (2) nicotine containing EC aerosol to assess real world performance against EC aerosol and nicotine capture efficiency. The salt challenge was used to determine baseline FE. Tap water was aerosolized into the environmental chamber using a small ultrasonic humidifier (Pure Enrichment MistAireTM, PEHUMSML). The salt aerosol produced had a geometric mean particle size of 113 nm and GSD of 1.68, as measured by a surface mobility particle sizer (TSI 3080, Electrostatic Classifier, Condensation Particle Counter Model 3775). The PAP was set to the lowest setting, and the exhaust was connected to the chamber exhaust duct so that air passed through the PAP only once, preventing water vapor buildup within the chamber and filter wetting. This setup was designed to promote evaporation of the water droplets and EC aerosol.
After the salt challenge, EC aerosol was manually puffed into the chamber for 15 min at approximately three puffs per minute. To start the EC challenge, three puffs were administered as rapidly as possible, then the nicotine sampling cassettes were turned on at 2 L/min. Each EC challenge puff was approximately 500 mL over 3 s at 50 watts with a lab-prepared e-liquid solution at 34.2 mg/mL freebase nicotine. EC aerosol was generated with a “Mod” type EC (Smok R200 TC, SMOK Tech, Shenzhen Bay Tech-Eco Park, Nanshan District, Shenzhen, China) and Aspire Triton atomizer. The relatively high concentration of nicotine in the e-liquid was to ensure analytical detection capability at the downstream sample location over a 15-min sample time at 99% capture efficiency. After the 15-min sample period, the nicotine samplers and PM monitors were turned off, and the nicotine samplers were removed as quickly as possible. Nicotine was extracted and analyzed using the method developed by Oni et al. [39]. Nicotine collected and PM monitored within the chamber (upstream) and within the exhaust duct (downstream) were compared to determine nicotine capture efficiency (Equation (1)) and FE. This procedure was performed for treated and untreated HEPA filters for both original and replacement filter types. For particulate FE, the total count concentration values were used. The source data are provided in the supplementary materials.
F E   o r   C E = 1 − P M   o r   N i c o t i n e   C o n c e n t r a t i o n   w i t h i n   t h e   c h a m b e r P M   o r   N i c o t i n e   C o n c e n t r a t i o n   w i t h i n   t h e   e x h a u s t   h o o d × 100
where:
FE = filtration efficiency, corresponds to particulate matter
CE = capture efficiency, corresponds to nicotine measurement
PM = particulate matter expressed as count concentration.

3. Results

3.1. Filtration Efficiency (FE) for Salt Aerosols

Mean FE (RSD) of untreated, original HEPA filters was 99.9% (0.06) and was significantly higher (p < 0.001) than that of untreated, replacement HEPA filters (94.4% (1.68)) (See Figure 3). Because the FE of original and replacement filters were significantly different, they were explored separately throughout the rest of the experimental design.
Mean FE (RSD) of untreated and citric acid-treated original HEPA filters were 99.8% (0.2) and 99.8% (0.1) respectively. The data was normally distributed (Shapiro-Wilks, W = 0.952, p = 0.73). There was no significant difference between treated and untreated filters (p = 0.84). Among the replacement HEPA filters, mean FE (RSD) for untreated and citric acid-treated HEPA filters was 89.8% (5.0) and 93.9% (3.8), respectively. This data was also normally distributed (Shapiro-Wilks, W = 0.889, p = 0.053). There was no significant difference in FE between the treated and untreated filters (p = 0.062). There was a significant difference between the treated original (99.8%) and treated replacement (93.9%) filters (t = 4.65, p = 0.002) and untreated original (99.8%) and untreated replacement (89.8%) filters (t = 6.31, p < 0.001) (See Table 4).

3.2. Filtration Efficiency for Electronic Cigarette Aerosols

Among the original HEPA filters, mean FE (RSD) for untreated HEPA filters was 96.4% (0.8) and for citric acid-treated HEPA filters was 94.7% (2.0). The data was normally distributed (Shapiro-Wilks, W = 0.869, p = 0.149) but there was no statistically significant difference between the untreated and citric acid-treated filters (t = −1.67, p = 0.172). However, among the replacement HEPA filters, mean FE (RSD) for untreated HEPA filters was 58.9% (14.9) and 75.4% (15.3) for citric acid-treated HEPA filters. The data was normally distributed (Shapiro-Wilks, W = 0.925, p = 0.230) and there was a statistically significant difference between the untreated and citric acid-treated filters (t = 3.09, p = 0.010). There was a statistically significant difference between the treated original (94.7%) and treated replacement (75.4%) filters (t = 4.74, p = 0.002). Similarly, there was a statistically significant difference between untreated original (96.4%) and untreated replacement (58.9%) filters (t = 11.99, p < 0.001) (See Table 4).

3.3. Nicotine Capture Efficiency

Original, untreated HEPA filters had mean nicotine capture efficiencies (RSD) of 57.4% (2.3) and original, treated HEPA filters were 99.4% (0.2). The data was not normally distributed (Shapiro-Wilks, W = 0.691, p = 0.002). There was a statistically significant difference between the untreated and citric acid-treated filters (Wilcoxon, W = 16, p = 0.029). Replacement, untreated HEPA filters had mean nicotine capture efficiencies (RSD) of 42.0% (14.2) and treated replacement HEPA filters had 99.0% (1.1). The data was also not normally distributed (Shapiro-Wilks, W = 0.737, p < 0.001) and there was also a statistically significant difference between the untreated and acid-treated filters (Wilcoxon, W = 64, p < 0.001). There was no statistically significant difference between the treated original (99.4%) and replacement (99.0%) filters (t = 1.19, p = 0.269). The untreated original filters (57.4%) were also not significantly different from the nicotine capture efficiency than the replacement (42.0%) filters (t = 3.78, p = 0.007) (See Table 4).

4. Discussion

HEPA filters are designed to have a 99.97% particle removal efficiency [43]. However, in this study, none of the air purifier filters attained this level of performance using our test setup. The challenge aerosol used in this study (salt aerosol challenge) was different from the standard EN 1822-1:2019 testing method for HEPA filters [41] which requires the use of dispersed oil particulate (DOP) aerosols. This difference is likely to overestimate the FE of the tested HEPA filters because salt does not coat fibers and neutralize charge to the degree that an oil particulate will. A noticeable difference was observed in the FE between the original and replacement filters, with the original filters coming close to the expected 99.97% FE, but falling short by ~0.07%. The replacement filters fell short by approximately 5%. The non-attainment of original filters to the true HEPA criteria could be due to minor air leakage around the filter element within the PAP unit, however the approximately 5% deficiency of replacement filters is likely due to lower quality of filter material. Each HEPA filter had a foam gasket to assist in sealing airflow, but none of the filters seemed to fit tightly when the PAP unit was fully assembled, if this were a source of major leakage then both the FE and nicotine capture efficiency would be limited proportional to the leakage and neither filter type would have performed close to the HEPA criteria.
The apparent differences in the original and replacement filters were also observed in a different brand, different style of PAP that was explored during scoping experiments. Although, replacement filters were “compatible” with the PAP unit and claimed to be HEPA, in our experience 2 out of 2 “off brand” replacement “HEPA” filters fell well short of the original “on-brand” FE. This implies that off-brand replacement filters marketed as “true HEPA” and “HEPA replacement” may be of inferior quality compared to on-brand filters and may not attain the level of air purification expected. Furthermore, the replacement filters were found to have higher air flowrates and larger masses, and more pleats than the original filters. The higher airflow rate is in-line with greater mass and number of pleats in the replacement filters. Interestingly, the proportion of additional pleats (1.11) was similar to the proportion of excess mass (1.13), which strongly suggests that the increase in mass is primarily due to more filter media present in the replacement filters. If the filter material in the replacement filters was equivalent to that in the original filters, these differences are expected to result in lower resistance to flow, greater PAP flowrate, lower face velocity and greater filtration efficiency. However, the FE of the replacements was significantly lower than originals which strongly suggests that the quality of the filtration media is different and inferior. Two possible explanations for these differences are larger fiber diameters and lower electrostatic properties in the replacement filters compared to the original filters. These differences would explain the poorer collection efficiency even with lower face velocity and greater residence time within the filter media. However, we were unable to perform tests to verify this. Lastly, it was also observed that the variability in mass was significantly greater in the replacement filters. We suspect this was caused by greater variation in quantity of glue used in the filters’ construction and weight of activated carbon mesh added.
Interestingly, it was observed that none of the tested “HEPA” filters met true HEPA specifications of 99.97% FE. This may be due to methodological differences in our evaluation and the manufacturers, specifically; (1) Differences in our salt aerosol and the aerosol used to evaluate the HEPA filters by the manufacturer and (2) Low level leakage between the filter and the PAP housing. Although we observed the FE of on-brand filters to be significantly lower than the HEPA criteria, these filters are nonetheless expected to provide efficient reduction of airborne particulates. Off-brand, replacement filters had significantly lower FE for salt aerosol (~5%) and substantially poor FE for EC aerosol (~50%) revealing a greater disparity in quality if applied to capture EC aerosol.
Interestingly, the FE for replacement filters was significantly improved for EC aerosol when treated with citric acid. This is likely due to absorption of nicotine by the citric acid as aerosol droplets pass through the filter matrix. However, the negative impact of EC aerosol on filtration efficiency of HEPA filters remains to be understood.
Most notably, both the original and replacement HEPA filters treated with citric acid successfully removed ≥99% nicotine from the airstream passing through them. Although all the HEPA filters used in this study had an inner mesh layer of activated carbon, untreated HEPA filters could only remove approximately 50% of nicotine passing through them.

Limitations

Filtration efficiency tests were not performed in accordance with EN 1822-1:2019 testing method for HEPA filters. This study was designed to evaluate the real-world performance of HEPA filters when used in a PAP and when treated with citric acid. Using DOP to challenge these filters could have impacted the citric acid treatment and would not supply nicotine for the determination of nicotine capture efficiency. This study was focused on assessing a low-cost, novel approach to reducing both particulate and nicotine exposure and therefore sought to use a representative aerosol for assessments, electronic cigarette aerosol. Salt aerosol was used as an internal reference and is not suitable for determining true HEPA performance.
Only one brand of original and replacement HEPA filters was evaluated in this study. Although preliminary trials with a different brand PAP and HEPA filter resulted in similar findings, these results may not apply to all PAP brands nor to all replacement filters.
Filtration accuracy and flow resistance were not measured in this study because these parameters were not crucial to the main objective of this study. In this study, the loading of citric acid on HEPA filters was minimal and not expected to impact flow resistance.
Loading citric acid on HEPA filters to increase their nicotine absorption capacity may increase the resistance to flow which could decrease the flow rate of the HEPA filter when used in the PAP designed by the manufacturer. However, the degree of loading used in this study did not cause a significant change in flow rate for either filter type.
The performance of the HEPA filters against tobacco cigarette smoke was not assessed in this study. Although we expect similar or better performance, this should be verified. It is noteworthy that elimination of indoor smoking is the best way to reduce the harms from tobacco smoking. However, we recognize that many persons exposed to secondhand smoke are unable to prevent smoking by other occupants in indoor settings and this study’s approach provides a means of protection in such instances.
Nicotine absorption capacity of acid-treated HEPA filters may be reduced in the presence of other sources of basic gases and vapors such as ammonia.

5. Conclusions

The citric acid treatment technique used in this study was highly effective at capturing nicotine (≥99%) even among HEPA filters with poor EC aerosol FE (42%, replacement filters). EC aerosol is more challenging to capture than salt aerosol. Replacement filters marketed as “equivalent” and “compatible” may have substantially lower FE than original, on-brand filters. Findings from this study demonstrate that citric acid-treated HEPA are likely to be an effective, efficient and practical strategy for reducing both PM and nicotine exposures in indoor settings.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/air3010008/s1, Table S1. Filtration Efficiency between Untreated Original and Replacement HEPA Filters with Salt Aerosol; Table S2. Filtration Efficiency of HEPA Filters challenged with Salt Aerosol; Table S3. Filtration Efficiency of HEPA Filters for Electronic Cigarette Aerosol; Table S4. Nicotine Capture Efficiency of HEPA Filters.

Author Contributions

Conceptualization, T.M.O. and E.L.F.; Methodology, T.M.O., C.C. and E.L.F.; Formal analysis, T.M.O. and E.L.F.; Investigation, T.M.O.; Resources, C.C. and E.L.F.; Data curation, T.M.O.; Writing—original draft, T.M.O.; Writing—review & editing, T.M.O., C.C. and E.L.F.; Supervision, E.L.F.; Funding acquisition, T.M.O. and E.L.F. All authors have read and agreed to the published version of the manuscript.

Funding

Research reported in this publication was supported by the Southwest Center for Occupational and Environmental Health (SWCOEH), the Centers for Disease Control and Prevention (CDC)/National Institute for Occupational Safety and Health (NIOSH) Education and Research Center (grant # T42OH008421) at The University of Texas Health Science Center at Houston (UTHealth) School of Public Health.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The raw data supporting the conclusions of this article will be made available by the authors on request.

Acknowledgments

The authors appreciate the staff of the Department of Occupational and Environmental Health, Hudson College of Public Health, University of Oklahoma Health Sciences Center for their support during this study.

Conflicts of Interest

The authors declare no conflict of interest relating to the material presented in this Article. Its contents, including any opinions and/or conclusions expressed, are solely those of the authors.

References

  1. Chilmonczyk, B.A.; Salmun, L.M.; Megathlin, K.N.; Neveux, L.M.; Palomaki, G.E.; Knight, G.J.; Pulkkinen, A.J.; Haddow, J.E. Association between exposure to environmental tobacco smoke and exacerbations of asthma in children. N. Engl. J. Med. 1993, 328, 1665–1669. [Google Scholar] [CrossRef] [PubMed]
  2. Charoenca, N.; Kungskulniti, N.; Tipayamongkholgul, M.; Sujirarat, D.; Lohchindarat, S.; Mock, J.; Hamann, S.L. Determining the burden of secondhand smoke exposure on the respiratory health of Thai children. Tob. Induc. Dis. 2013, 11, 7. [Google Scholar] [CrossRef]
  3. Håberg, S.E.; Stigum, H.; Nystad, W.; Nafstad, P. Effects of pre-and postnatal exposure to parental smoking on early childhood respiratory health. Am. J. Epidemiol. 2007, 166, 679–686. [Google Scholar] [CrossRef] [PubMed]
  4. Duijts, L.; Jaddoe, V.W.; Hofman, A.; Steegers, E.A.; Mackenbach, J.P.; de Jongste, J.C.; Moll, H.A. Maternal smoking in prenatal and early postnatal life and the risk of respiratory tract infections in infancy. The Generation R study. Eur. J. Epidemiol. 2008, 23, 547–555. [Google Scholar] [CrossRef]
  5. Best, D.; Committee on Environmental Health; Committee on Native American Child Health and Committee on Adolescence. Secondhand and prenatal tobacco smoke exposure. Pediatrics 2009, 124, e1017–e1044. [Google Scholar] [CrossRef]
  6. Tang, D.; Warburton, D.; Tannenbaum, S.R.; Skipper, P.; Santella, R.M.; Cereijido, G.S.; Crawford, F.G.; Perera, F.P. Molecular and genetic damage from environmental tobacco smoke in young children. Cancer Epidemiol. Biomark. Prev. 1999, 8, 427–431. [Google Scholar]
  7. Barnoya, J.; Glantz, S.A. Cardiovascular effects of secondhand smoke: Nearly as large as smoking. Circulation 2005, 111, 2684–2698. [Google Scholar] [CrossRef]
  8. Glantz, S.A.; Parmley, W.W. Passive smoking and heart disease. Epidemiology, physiology, and biochemistry. Circulation 1991, 83, 1–12. [Google Scholar] [CrossRef]
  9. Öberg, M.; Jaakkola, M.S.; Woodward, A.; Peruga, A.; Prüss-Ustün, A. Worldwide burden of disease from exposure to second-hand smoke: A retrospective analysis of data from 192 countries. Lancet 2011, 377, 139–146. [Google Scholar] [CrossRef]
  10. Naeem, Z. Second-hand smoke–ignored implications. Int. J. Health Sci. 2015, 9, V. [Google Scholar] [CrossRef]
  11. Barnoya, J.; Navas-Acien, A. Protecting the world from secondhand tobacco smoke exposure: Where do we stand and where do we go from here? Nicotine Tob. Res. 2012, 15, 789–804. [Google Scholar] [CrossRef]
  12. Mescolo, F.; Ferrante, G.; La Grutta, S. Effects of e-cigarette exposure on prenatal life and childhood respiratory health: A review of current evidence. Front. Pediatr. 2021, 9, 711573. [Google Scholar] [CrossRef] [PubMed]
  13. Kim, S.Y.; Sim, S.; Choi, H.G. Active, passive, and electronic cigarette smoking is associated with asthma in adolescents. Sci. Rep. 2017, 7, 17789. [Google Scholar] [CrossRef]
  14. Schweitzer, R.J.; Wills, T.A.; Tam, E.; Pagano, I.; Choi, K. E-cigarette use and asthma in a multiethnic sample of adolescents. Prev. Med. 2017, 105, 226–231. [Google Scholar] [CrossRef]
  15. Cho, J.H.; Paik, S.Y. Association between electronic cigarette use and asthma among high school students in South Korea. PLoS ONE 2016, 11, e0151022. [Google Scholar] [CrossRef]
  16. Islam, T.; Braymiller, J.; Eckel, S.P.; Liu, F.; Tackett, A.P.; Rebuli, M.E.; Barrington-Trimis, J.; McConnell, R. Secondhand nicotine vaping at home and respiratory symptoms in young adults. Thorax 2022, 77, 663–668. [Google Scholar] [CrossRef] [PubMed]
  17. Lee, M.-S.; Rees, V.W.; Koutrakis, P.; Wolfson, J.M.; Son, Y.-S.; Lawrence, J.; Christiani, D.C. Cardiac autonomic effects of secondhand exposure to nicotine from electronic cigarettes: An exploratory study. Environ. Epidemiol. 2019, 3, e033. [Google Scholar] [CrossRef]
  18. National Cancer Institute. Secondhand Tobacco Smoke (Environmental Tobacco Smoke). 13 June 2024. Available online: https://www.cancer.gov/about-cancer/causes-prevention/risk/substances/secondhand-smoke#:~:text=What%20is%20secondhand%20tobacco%20smoke,involuntary%20smoke%2C%20and%20passive%20smoke (accessed on 24 July 2024).
  19. Gatlin, C.G. IARC classifies formaldehyde as carcinogenic. Oncol. Times 2004, 26, 72. [Google Scholar]
  20. Logue, J.M.; Sleiman, M.; Montesinos, V.N.; Russell, M.L.; Litter, M.I.; Benowitz, N.L.; Gundel, L.A.; Destaillats, H. Emissions from electronic cigarettes: Assessing vapers’ intake of toxic compounds, secondhand exposures, and the associated health impacts. Environ. Sci. Technol. 2017, 51, 9271–9279. [Google Scholar] [CrossRef]
  21. Offermann, F.J. Chemical emissions from e-cigarettes: Direct and indirect (passive) exposures. Build. Environ. 2015, 93, 101–105. [Google Scholar] [CrossRef]
  22. Kapiamba, K.F.; Hao, W.; Owusu, S.Y.; Liu, W.; Huang, Y.-W.; Wang, Y. Examining metal contents in primary and secondhand aerosols released by electronic cigarettes. Chem. Res. Toxicol. 2022, 35, 954–962. [Google Scholar] [CrossRef] [PubMed]
  23. Saffari, A.; Daher, N.; Ruprecht, A.; De Marco, C.; Pozzi, P.; Boffi, R.; Hamad, S.H.; Shafer, M.M.; Schauer, J.J.; Westerdahl, D. Particulate metals and organic compounds from electronic and tobacco-containing cigarettes: Comparison of emission rates and secondhand exposure. Environ. Sci. Process. Impacts 2014, 16, 2259–2267. [Google Scholar] [CrossRef]
  24. Ting, C.Y.; Ahmad Sabri, N.A.; Tiong, L.L.; Zailani, H.; Wong, L.P.; Agha Mohammadi, N.; Anchah, L. Heavy metals (Cr, Pb, Cd, Ni) in aerosols emitted from electronic cigarettes sold in Malaysia. J. Environ. Sci. Health Part A 2020, 55, 55–62. [Google Scholar] [CrossRef] [PubMed]
  25. United States Environmental Protection Agency. Secondhand Smoke and Electronic-Cigarette Aerosols. 13 December 2024. Available online: https://www.epa.gov/indoor-air-quality-iaq/secondhand-smoke-and-electronic-cigarette-aerosols (accessed on 8 February 2025).
  26. Cooper, E.; Wang, Y.; Stamp, S.; Nijsen, T.; de Graaf, P.; Hofman, J.; Inki, T.; Driessen, R.; Liebmann, J.; Geven, I.T. Why do people use portable air purifiers? Evidence from occupant surveys and air quality monitoring in homes in three European cities. Build. Res. Inf. 2022, 50, 213–229. [Google Scholar] [CrossRef]
  27. Zhan, Y.; Johnson, K.; Norris, C.; Shafer, M.M.; Bergin, M.H.; Zhang, Y.; Zhang, J.; Schauer, J.J. The influence of air cleaners on indoor particulate matter components and oxidative potential in residential households in Beijing. Sci. Total Environ. 2018, 626, 507–518. [Google Scholar] [CrossRef]
  28. Aldekheel, M.; Altuwayjiri, A.; Tohidi, R.; Jalali Farahani, V.; Sioutas, C. The role of portable air purifiers and effective ventilation in improving indoor air quality in university classrooms. Int. J. Environ. Res. Public Health 2022, 19, 14558. [Google Scholar] [CrossRef]
  29. Chen, R.; Zhao, A.; Chen, H.; Zhao, Z.; Cai, J.; Wang, C.; Yang, C.; Li, H.; Xu, X.; Ha, S. Cardiopulmonary benefits of reducing indoor particles of outdoor origin: A randomized, double-blind crossover trial of air purifiers. J. Am. Coll. Cardiol. 2015, 65, 2279–2287. [Google Scholar] [CrossRef]
  30. Christopherson, D.A.; Yao, W.C.; Lu, M.; Vijayakumar, R.; Sedaghat, A.R. High-efficiency particulate air filters in the era of COVID-19: Function and efficacy. Otolaryngol.–Head Neck Surg. 2020, 163, 1153–1155. [Google Scholar] [CrossRef]
  31. White, E. HEPA and ULPA filters. J. Valid. Technol. 2009, 15, 48. [Google Scholar]
  32. Bennett, A. Standards and testing: Meeting standards in filter media. Filtr. Sep. 2012, 49, 22–25. [Google Scholar] [CrossRef]
  33. Lowther, S.D.; Deng, W.; Fang, Z.; Booker, D.; Whyatt, D.J.; Wild, O.; Wang, X.; Jones, K.C. How efficiently can HEPA purifiers remove priority fine and ultrafine particles from indoor air? Environ. Int. 2020, 144, 106001. [Google Scholar] [CrossRef] [PubMed]
  34. Shaughnessy, R.J.; Levetin, E.; Blocker, J.; Sublette, K.L. Effectiveness of portable indoor air cleaners: Sensory testing results. Indoor Air 1994, 4, 179–188. [Google Scholar] [CrossRef]
  35. Agranovski, I.; Moustafa, S.; Braddock, R. Performance of activated carbon loaded fibrous filters on simultaneous removal of particulate and gaseous pollutants. Environ. Technol. 2005, 26, 757–766. [Google Scholar] [CrossRef] [PubMed]
  36. Kim, S.; Yoon, Y.; Kim, K. Performance of activated carbon-impregnated cellulose filters for indoor VOCs and dust control. Int. J. Environ. Sci. Technol. 2016, 13, 2189–2198. [Google Scholar] [CrossRef]
  37. Zhang, L.; Lin, Y.; Zhu, Y. Transport and mitigation of exhaled electronic cigarette aerosols in a multizone indoor environment. Aerosol Air Qual. Res. 2020, 20, 2536–2547. [Google Scholar] [CrossRef]
  38. Hammond, S.K.; Leaderer, B.P.; Roche, A.C.; Schenker, M. Collection and analysis of nicotine as a marker for environmental tobacco smoke. Atmos. Environ. 1967 1987, 21, 457–462. [Google Scholar] [CrossRef]
  39. Oni, T.M.; Gamagedara, S.; Floyd, E.L. Desorption efficiency and holding capacity of acid-treated filters for nicotine sampling in vape shops. Ann. Work Expo. Health 2024, 69, 104–108. [Google Scholar] [CrossRef]
  40. Aquilina, N.J.; Havel, C.M.; Harrison, R.M.; Ho, K.-F.; Benowitz, N.L.; Jacob, P., III. Determination of 4-(Methylnitrosamino)-1-(3-Pyridyl)-1-Butanone (NNK) arising from tobacco smoke in airborne particulate matter. Environ. Int. 2022, 158, 106992. [Google Scholar] [CrossRef]
  41. EN 1822-1:2019; High Efficiency Air Filters (EPA, HEPA and ULPA)—Part 1: Classification, Performance Testing, Marking; German Version. iTeh Standards: Etobicoke, ON, Canada, 2019.
  42. Mead-Hunter, R.; King, A.J.; Mullins, B.J. Aerosol-mist coalescing filters—A review. Sep. Purif. Technol. 2014, 133, 484–506. [Google Scholar] [CrossRef]
  43. USEPA. What Is a HEPA Filter? 2024. Available online: https://www.epa.gov/indoor-air-quality-iaq/what-hepa-filter (accessed on 12 March 2024).
Air 03 00008 g001
Figure 1. HEPA filter types used in this study left panel shows original filter and right panel shows replacement filter. Filter components; (a) Pre-filter screen and pleated filter (b) Gasket (c) Activated carbon filter.
Figure 1. HEPA filter types used in this study left panel shows original filter and right panel shows replacement filter. Filter components; (a) Pre-filter screen and pleated filter (b) Gasket (c) Activated carbon filter.
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Air 03 00008 g002
Figure 2. Environmental chamber set-up for treating filters with citric acid, testing their filtration efficiency, and nicotine capture efficiency.
Figure 2. Environmental chamber set-up for treating filters with citric acid, testing their filtration efficiency, and nicotine capture efficiency.
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Figure 3. Filtration Efficiency (%) between Untreated Original and Replacement HEPA Filters with Salt Aerosol.
Figure 3. Filtration Efficiency (%) between Untreated Original and Replacement HEPA Filters with Salt Aerosol.
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Table 1. Flowrates of air purifiers with the different HEPA filters on the lowest fan setting.
Table 1. Flowrates of air purifiers with the different HEPA filters on the lowest fan setting.
Air PurifierHEPA Filter NumberAir Flowrate (m3/min)
Untreated HEPA FiltersTreated HEPA Filters
OriginalReplacementOriginalReplacement
114.645.014.795.10
214.535.074.625.04
314.624.874.705.01
414.704.874.645.13
12 4.98 4.67
22 4.84 4.67
32 4.70 4.87
42 4.96 4.90
Average4.624.914.694.92
SD0.070.120.070.18
Table 2. Mass of HEPA Filters.
Table 2. Mass of HEPA Filters.
HEPA Filter NumberMass (Grams)
Untreated HEPA FiltersTreated HEPA Filters
OriginalReplacementOriginalReplacement
1748.5859.9703.9796.4
2733.3775.2746.5864.5
3737.9796.9724859.4
4734.7841754.5873.7
5 823.7 910.5
6 844.8 868.9
7 817 896.6
8 836.3 805.5
Average739824732859
SD6.8827.5822.8839.98
Table 3. Number of HEPA Filter Pleats.
Table 3. Number of HEPA Filter Pleats.
HEPA FilterNumber of Pleats
OriginalReplacement
1152177
2160177
3158179
4159178
Average157178
SD3.590.96
Table 4. Filtration/Capture Efficiencies of HEPA Filters for Salt Aerosol, EC Aerosol and Nicotine Vapor.
Table 4. Filtration/Capture Efficiencies of HEPA Filters for Salt Aerosol, EC Aerosol and Nicotine Vapor.
Filtration/Capture Efficiency
Challenge
Agent		Filter TypeUntreatedCitric Acid-Treatedp-Value
Mean (%)RSDMean (%)RSD
Salt AerosolOriginals99.80.299.80.10.840
Replacements89.85.093.93.80.062
EC AerosolOriginals96.40.894.72.00.172
Replacements58.914.975.415.30.010 *
Nicotine VaporOriginals57.42.399.40.20.029 *
Replacements42.014.299.01.1<0.001 *
* p < 0.05.
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MDPI and ACS Style

Oni, T.M.; Cai, C.; Floyd, E.L. Efficacy of Acid-Treated HEPA Filters for Dual Sequestration of Nicotine and Particulate Matter. Air 2025, 3, 8. https://doi.org/10.3390/air3010008

AMA Style

Oni TM, Cai C, Floyd EL. Efficacy of Acid-Treated HEPA Filters for Dual Sequestration of Nicotine and Particulate Matter. Air. 2025; 3(1):8. https://doi.org/10.3390/air3010008

Chicago/Turabian Style

Oni, Toluwanimi M., Changjie Cai, and Evan L. Floyd. 2025. "Efficacy of Acid-Treated HEPA Filters for Dual Sequestration of Nicotine and Particulate Matter" Air 3, no. 1: 8. https://doi.org/10.3390/air3010008

APA Style

Oni, T. M., Cai, C., & Floyd, E. L. (2025). Efficacy of Acid-Treated HEPA Filters for Dual Sequestration of Nicotine and Particulate Matter. Air, 3(1), 8. https://doi.org/10.3390/air3010008

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