The Mila Definitive Guide to IAQ Efficacy and Application of Air Purifiers

4.5 — Air Purifiers vs. Outdoor-Origin Pollutant Sources

Air purifiers provide critical protection from outdoor pollution that infiltrates indoors. By filtering smoke from fires and exhaust from traffic, they reduce exposure when outdoor air is unsafe, helping maintain healthier indoor environments.

Outdoor pollution readily enters buildings, driving short-term spikes and prolonged episodes of poor IAQ. These sources release fine and ultrafine particles along with harmful gases that infiltrate through leaks, cracks, and ventilation openings, exposing occupants even when doors and windows are closed. Air purifiers serve as a practical line of defense, supplementing building envelopes and HVAC filtration by capturing outdoor-derived pollutants indoors.

Controlled and field research consistently shows that portable air cleaners protect against indoor pollution from wildfire smoke. Chamber experiments demonstrate that both HEPA and well-constructed do-it-yourself units effectively remove particles generated from wildfire smoke proxies, though performance can decline as filters load. Field campaigns across homes, offices, and community facilities confirm similar real-world performance. In wildfire-impacted residences, HEPA-based devices cut indoor PM2.5 by 48–78% in Seattle and 30–74% in Australia, while data from Canada found infiltration factors falling by roughly half when air purifiers operated. Office trials reported 73–92% PM2.5 reductions, and community facilities serving vulnerable groups observed 63–89% less time spent in “unhealthy” air quality ranges. Modeling and review analyses reinforce these results: national and regional assessments identify portable air cleaners as among the most effective interventions for wildfire smoke, capable of preventing up to 63% of hospitalizations and 39% of deaths linked to PM2.5.

Air purifiers lower indoor exposure to traffic-related air pollution, removing PM that infiltrates from nearby roadways. Laboratory testing confirms that they effectively capture diesel exhaust aerosols, achieving higher removal efficiency than when tested with standard particles. In a field study including 46 near-roadway homes, median indoor PM2.5 decreased from 7.6 µg/m³ to 3.4 µg/m³ and black carbon from 0.6 µg/m³ to 0.1 µg/m³ when air cleaners were deployed, while in a bus maintenance workshop, portable devices cut PM2.5 and PM10 by roughly 45–53% and elemental carbon by 46%, demonstrating consistent mitigation across residential and occupational environments.

Air purifiers meaningfully limit indoor exposure to wildfire smoke and traffic-related emissions. Combined with measures such as sealing, filtration, and ventilation control, they offer one of the most effective and accessible ways to maintain cleaner air during severe outdoor pollution events.

References

Aldekheel, M., Altuwayjiri, A., Tohidi, R., Jalali Farahani, V., & Sioutas, C. (2022). The Role of Portable Air Purifiers and Effective Ventilation in Improving Indoor Air Quality in University Classrooms. International Journal of Environmental Research and Public Health, 19(21), 14558. https://doi.org/10.3390/ijerph192114558

Alvarenga, M. O. P., Dias, J. M. M., Lima, B. J. L. A., Gomes, A. S. L., & Monteiro, G. Q. M. (2023). The implementation of portable air-cleaning technologies in healthcare settings – a scoping review. Journal of Hospital Infection, 132, 93–103. https://doi.org/10.1016/j.jhin.2022.12.004

Ardkapan, S. R., Afshari, A., & Bergsøe, N. C. (2015). Performance and effectiveness of portable air cleaners in an office room: An experimental study. Journal of Civil Engineering and Architecture, 9(7), 757–766.

Arıkan, İ., Genç, Ö., Uyar, C., Tokur, M. E., Balcı, C., & Perçin Renders, D. (2022). Effectiveness of air purifiers in intensive care units: An intervention study. Journal of Hospital Infection, 120, 14–22. https://doi.org/10.1016/j.jhin.2021.10.011

Azevedo, A., Liddie, J., Liu, J., Schiff, J. E., Adamkiewicz, G., & Hart, J. E. (2022). Effects of portable air cleaners and A/C unit fans on classroom concentrations of particulate matter in a non-urban elementary school. PLOS ONE, 17(12), e0278046. https://doi.org/10.1371/journal.pone.0278046

Bard, R. L., Rubenfire, M., Fink, S., Bryant, J., Wang, L., Speth, K., Zhou, N., Morishita, M., & Brook, R. D. (2020). Reduced Fine Particulate Matter Air Pollution Exposures Using In-Home Portable Air Cleaners: PILOT RESULTS OF THE CARDIAC REHABILITATION AIR FILTER TRIAL (CRAFT). Journal of Cardiopulmonary Rehabilitation and Prevention, 40(4), 276. https://doi.org/10.1097/HCR.0000000000000516

Barn, P., Gombojav, E., Ochir, C., Laagan, B., Beejin, B., Naidan, G., Boldbaatar, B., Galsuren, J., Byambaa, T., Janes, C., Janssen, P. A., Lanphear, B. P., Takaro, T. K., Venners, S. A., Webster, G. M., Yuchi, W., Palmer, C. D., Parsons, P. J., Roh, Y. M., & Allen, R. W. (2018). The effect of portable HEPA filter air cleaners on indoor PM2.5 concentrations and second hand tobacco smoke exposure among pregnant women in Ulaanbaatar, Mongolia: The UGAAR randomized controlled trial. Science of The Total Environment, 615, 1379–1389. https://doi.org/10.1016/j.scitotenv.2017.09.291

Barn, P. K., Elliott, C. T., Allen, R. W., Kosatsky, T., Rideout, K., & Henderson, S. B. (2016). Portable air cleaners should be at the forefront of the public health response to landscape fire smoke. Environmental Health, 15(1), 116. https://doi.org/10.1186/s12940-016-0198-9

Buising, K. L., Schofield, R., Irving, L., Keywood, M., Stevens, A., Keogh, N., Skidmore, G., Wadlow, I., Kevin, K., Rismanchi, B., Wheeler, A. J., Humphries, R. S., Kainer, M., Monty, J., McGain, F., & Marshall, C. (2022). Use of portable air cleaners to reduce aerosol transmission on a hospital coronavirus disease 2019 (COVID-19) ward. Infection Control & Hospital Epidemiology, 43(8), 987–992. https://doi.org/10.1017/ice.2021.284

Cai, J., Yu, W., Li, B., Yao, R., Zhang, T., Guo, M., Wang, H., Cheng, Z., Xiong, J., Meng, Q., & Kipen, H. (2019). Particle removal efficiency of a household portable air cleaner in real-world residences: A single-blind cross-over field study. Energy and Buildings, 203, 109464. https://doi.org/10.1016/j.enbuild.2019.109464

Castellini, J. E., Faulkner, C. A., Zuo, W., Lorenzetti, D. M., & Sohn, M. D. (2022). Assessing the use of portable air cleaners for reducing exposure to airborne diseases in a conference room with thermal stratification. Building and Environment, 207, 108441. https://doi.org/10.1016/j.buildenv.2021.108441

Cheng, Y. S., Lu, J. C., & Chen, T. R. (1998). Efficiency of a Portable Indoor Air Cleaner in Removing Pollens and Fungal Spores. Aerosol Science and Technology, 29(2), 92–101. https://doi.org/10.1080/02786829808965554

Cortellessa, G., Canale, C., Stabile, L., Grossi, G., Buonanno, G., & Arpino, F. (2023). Effectiveness of a portable personal air cleaner in reducing the airborne transmission of respiratory pathogens. Building and Environment, 235, 110222. https://doi.org/10.1016/j.buildenv.2023.110222

Cox, J., Isiugo, K., Ryan, P., Grinshpun, S. A., Yermakov, M., Desmond, C., Jandarov, R., Vesper, S., Ross, J., Chillrud, S., Dannemiller, K., & Reponen, T. (2018). Effectiveness of a portable air cleaner in removing aerosol particles in homes close to highways. Indoor Air, 28(6), 818–827. https://doi.org/10.1111/ina.12502

Dubey, S., Rohra, H., & Taneja, A. (2021). Assessing effectiveness of air purifiers (HEPA) for controlling indoor particulate pollution. Heliyon, 7(9). https://doi.org/10.1016/j.heliyon.2021.e07976

Duill, F. F., Schulz, F., Jain, A., van Wachem, B., & Beyrau, F. (2023). Comparison of Portable and Large Mobile Air Cleaners for Use in Classrooms and the Effect of Increasing Filter Loading on Particle Number Concentration Reduction Efficiency. Atmosphere, 14(9), 1437. https://doi.org/10.3390/atmos14091437

Ebrahimifakhar, A., Poursadegh, M., Hu, Y., Yuill, D. P., & Luo, Y. (2024). A systematic review and meta-analysis of field studies of portable air cleaners: Performance, user behavior, and by-product emissions. Science of The Total Environment, 912, 168786. https://doi.org/10.1016/j.scitotenv.2023.168786

Faridi, S., Allen, R. W., Brook, R. D., Yousefian, F., Hassanvand, M. S., & Carlsten, C. (2023). An updated systematic review and meta-analysis on portable air cleaners and blood pressure: Recommendations for users and manufacturers. Ecotoxicology and Environmental Safety, 263, 115227. https://doi.org/10.1016/j.ecoenv.2023.115227

Gür, M., & Kılıç, M. (2024). Assessment of a Portable Air Cleaning Device Performance in Eliminating Indoor Air Contaminants by Considering Particle Transport Characteristics. Applied Sciences, 14(18), 8362. https://doi.org/10.3390/app14188362

Hansel, N. N., Putcha, N., Woo, H., Peng, R., Diette, G. B., Fawzy, A., Wise, R. A., Romero, K., Davis, M. F., Rule, A. M., Eakin, M. N., Breysse, P. N., McCormack, M. C., & Koehler, K. (2022). Randomized Clinical Trial of Air Cleaners to Improve Indoor Air Quality and Chronic Obstructive Pulmonary Disease Health: Results of the CLEAN AIR Study. American Journal of Respiratory and Critical Care Medicine, 205(4), 421–430. https://doi.org/10.1164/rccm.202103-0604OC

Hart, J. F., Ward, T. J., Spear, T. M., Rossi, R. J., Holland, N. N., & Loushin, B. G. (2011). Evaluating the Effectiveness of a Commercial Portable Air Purifier in Homes with Wood Burning Stoves: A Preliminary Study. Journal of Environmental and Public Health, 2011(1), 324809. https://doi.org/10.1155/2011/324809

Huang, C.-H., Bui, T., Hwang, D., Shirai, J., Austin, E., Cohen, M., Gould, T., Larson, T., Novosselov, I., Tan, S., Fox, J., & Seto, E. (2023). Assessing the effectiveness of portable HEPA air cleaners for reducing particulate matter exposure in King County, Washington homeless shelters: Implications for community congregate settings. Science of The Total Environment, 891, 164402. https://doi.org/10.1016/j.scitotenv.2023.164402

Huang, C.-H., Xiang, J., Austin, E., Shirai, J., Liu, Y., Simpson, C., Karr, C. J., Fyfe-Johnson, A. L., Kronborg Larsen, T., & Seto, E. (2021). Impacts of using auto-mode portable air cleaner on indoor PM2.5 levels: An intervention study. Building and Environment, 188, 107444. https://doi.org/10.1016/j.buildenv.2020.107444

Karam, J., Katramiz, E., Ghali, K., & Ghaddar, N. (2022). Effective mitigation of cross-contamination in classroom conditioned by intermittent air jet cooling with use of portable air cleaners. Building and Environment, 219, 109220. https://doi.org/10.1016/j.buildenv.2022.109220

Li, Y., Kong, B., Cheng, M., Song, C., Jiang, Y., & Shi, H. (2024). Effectiveness of portable air cleaners in mitigating respiratory virus transmission risk. Physica Scripta, 99(4), 045021. https://doi.org/10.1088/1402-4896/ad32b5

Lu, F. T., Laumbach, R. J., Legard, A., Myers, N. T., Black, K. G., Ohman-Strickland, P., Alimokhtari, S., de Resende, A., Calderón, L., Mainelis, G., & Kipen, H. M. (2023). Real-World Effectiveness of Portable Air Cleaners in Reducing Home Particulate Matter Concentrations. Aerosol and Air Quality Research, 24(1), 230202. https://doi.org/10.4209/aaqr.230202

Ma, H., Shen, H., Shui, T., Li, Q., & Zhou, L. (2016). Experimental Study on Ultrafine Particle Removal Performance of Portable Air Cleaners with Different Filters in an Office Room. International Journal of Environmental Research and Public Health, 13(1), 102. https://doi.org/10.3390/ijerph13010102

McIntyre, A. M., Scammell, M. K., Kinney, P. L., Khosla, K., Benton, L., Bongiovanni, R., McCannon, J., & Milando, C. W. (2024). Portable Air Cleaner Usage and Particulate Matter Exposure Reduction in an Environmental Justice Community: A Pilot Study. Environmental Health Insights, 18, 11786302241258587. https://doi.org/10.1177/11786302241258587

Mølgaard, B., Koivisto, A. J., Hussein, T., & Hämeri, K. (2014). A New Clean Air Delivery Rate Test Applied to Five Portable Indoor Air Cleaners. Aerosol Science and Technology, 48(4), 409–417. https://doi.org/10.1080/02786826.2014.883063

Nahian, M. R., & Siegel, J. A. (2025). An in-situ test method for portable air cleaners. Building and Environment, 272, 112659. https://doi.org/10.1016/j.buildenv.2025.112659

Offermann, F. J., Sextro, R. G., Fisk, W. J., Grimsrud, D. T., Nazaroff, W. W., Nero, A. V., Revzan, K. L., & Yater, J. (1985). Control of respirable particles in indoor air with portable air cleaners. Atmospheric Environment (1967), 19(11), 1761–1771. https://doi.org/10.1016/0004-6981(85)90003-4

Park, H.-K., Cheng, K.-C., Tetteh, A. O., Hildemann, L. M., & Nadeau, K. C. (2017). Effectiveness of air purifier on health outcomes and indoor particles in homes of children with allergic diseases in Fresno, California: A pilot study. Journal of Asthma, 54(4), 341–346. https://doi.org/10.1080/02770903.2016.1218011

Qian, H., Li, Y., Sun, H., Nielsen, P. V., Huang, X., & Zheng, X. (2010). Particle removal efficiency of the portable HEPA air cleaner in a simulated hospital ward. Building Simulation, 3(3), 215–224. https://doi.org/10.1007/s12273-010-0005-4

Rodríguez, M., Palop, M. L., Seseña, S., & Rodríguez, A. (2021). Are the Portable Air Cleaners (PAC) really effective to terminate airborne SARS-CoV-2? Science of The Total Environment, 785, 147300. https://doi.org/10.1016/j.scitotenv.2021.147300

Sankhyan, S., K. Witteman, J., Coyan, S., Patel, S., & E. Vance, M. (2022). Assessment of PM 2.5 concentrations, transport, and mitigation in indoor environments using low-cost air quality monitors and a portable air cleaner. Environmental Science: Atmospheres, 2(4), 647–658. https://doi.org/10.1039/D2EA00025C

Sharma, R., & Balasubramanian, R. (2020). Evaluation of the effectiveness of a portable air cleaner in mitigating indoor human exposure to cooking-derived airborne particles. Environmental Research, 183, 109192. https://doi.org/10.1016/j.envres.2020.109192

Stauffer, D. A., Autenrieth, D. A., Hart, J. F., & Capoccia, S. (2020). Control of wildfire-sourced PM2.5 in an office setting using a commercially available portable air cleaner. Journal of Occupational and Environmental Hygiene, 17(4), 109–120. https://doi.org/10.1080/15459624.2020.1722314

Stinson, B. W., Greathouse, E. A., Kapileo, D., & Gall, E. T. (2025). Critical analysis of a school district-wide response to addressing indoor airborne disease transmission. Indoor Environments, 2(3), 100115. https://doi.org/10.1016/j.indenv.2025.100115

Stinson, B. W., Laguerre, A., & Gall, E. T. (2024). Particle and Gas-Phase Evaluation of Air Cleaners Under Indoor Wildfire Smoke Conditions. ACS ES&T Air, 1(6), 492–501. https://doi.org/10.1021/acsestair.3c00083

Sultan, Z., Li, J., Pantelic, J., & Schiavon, S. (2022). Indoor Air Pollution of Outdoor Origin: Mitigation Using Portable Air Cleaners in Singapore Office Building. Aerosol and Air Quality Research, 22(10), 220204. https://doi.org/10.4209/aaqr.220204

Sultan, Z. M., Nilsson, G. J., & Magee, R. J. (2011). Removal of ultrafine particles in indoor air: Performance of various portable air cleaner technologies. HVAC&R Research, 17(4), 513–525. https://doi.org/10.1080/10789669.2011.579219

Villanueva, F., Felgueiras, F., Notario, A., Cabañas, B., & Gabriel, M. F. (2024). Indoor Environmental Quality and Effectiveness of Portable Air Cleaners in Reducing Levels of Airborne Particles during Schools’ Reopening in the COVID-19 Pandemic. Sustainability, 16(15), 6549. https://doi.org/10.3390/su16156549

Ward, M., Siegel, J. A., & Corsi, R. L. (2005). The effectiveness of stand alone air cleaners for shelter-in-place. Indoor Air, 15(2), 127. https://doi.org/10.1111/j.1600-0668.2004.00326.x

Waring, M. S., Siegel, J. A., & Corsi, R. L. (2008). Ultrafine particle removal and generation by portable air cleaners. Atmospheric Environment, 42(20), 5003–5014. https://doi.org/10.1016/j.atmosenv.2008.02.011

Xiang, J., Huang, C.-H., Shirai, J., Liu, Y., Carmona, N., Zuidema, C., Austin, E., Gould, T., Larson, T., & Seto, E. (2021). Field measurements of PM2.5 infiltration factor and portable air cleaner effectiveness during wildfire episodes in US residences. Science of The Total Environment, 773, 145642. https://doi.org/10.1016/j.scitotenv.2021.145642

Yin, H., Li, Z., Zhai, X., Ning, Y., Gao, L., Cui, H., Ma, Z., & Li, A. (2023). Field measurement of the impact of natural ventilation and portable air cleaners on indoor air quality in three occupant states. Energy and Built Environment, 4(5), 601–613. https://doi.org/10.1016/j.enbenv.2022.05.004

Zhang, A., Liu, Y., Ji, J. S., & Zhao, B. (2023). Air Purifier Intervention to Remove Indoor PM2.5 in Urban China: A Cost-Effectiveness and Health Inequality Impact Study. Environmental Science & Technology, 57(11), 4492–4503. https://doi.org/10.1021/acs.est.2c09730

Zhu, X., Lv, M., & Yang, X. (2018). Performance of sorption-based portable air cleaners in formaldehyde removal: Laboratory tests and field verification. Building and Environment, 136, 177–184. https://doi.org/10.1016/j.buildenv.2018.03.030

Zuraimi, M. S., Vuotari, M., Nilsson, G., Magee, R., Kemery, B., & Alliston, C. (2017). Impact of dust loading on long term portable air cleaner performance. Building and Environment, 112, 261–269. https://doi.org/10.1016/j.buildenv.2016.11.001

It’s time to clear the air.

Get your Mila today
Shop Now