Portable Air Cleaners Research Articles

Fine particulate matter infiltration at Western Montana residences during wildfire season

Background/aimsWildfire air pollution is a growing public health concern as wildfires increase in size, intensity, and duration in the United States. The public is often encouraged to stay indoors during wildfire smoke events to reduce exposure. However, there is limited information on how much wildfire smoke infiltrates indoors at residences and what household/behavioral characteristics contribute to higher infiltration. We assessed fine particulate matter (PM2.5) infiltration into Western Montana residences during wildfire season. MethodsWe measured continuous outdoor and indoor PM2.5 concentrations from July–October 2022 at 20 residences in Western Montana during wildfire season using low-cost PM2.5 sensors. We used paired outdoor/indoor PM2.5 data from each household to calculate infiltration efficiency (Finf; range 0–1; higher values indicate more outdoor PM2.5 infiltration to the indoor environment) using previously validated methods. Analyses were conducted for all households combined and for various household subgroups. ResultsMedian (25th percentile, 75th percentile) daily outdoor PM2.5 at the households was 3.7 μg/m3 (2.1, 7.1) during the entire study period and 29.0 μg/m3 (19.0, 49.4) during a 2-week period in September impacted by wildfire smoke. Median daily indoor PM2.5 at the households was 2.5 μg/m3 (1.3, 5.5) overall and 10.4 μg/m3 (5.6, 21.0) during the wildfire period. Overall Finf was 0.34 (95 % Confidence Interval [95%CI]: 0.33, 0.35) with lower values during the wildfire period (0.32; 95%CI: 0.28, 0.36) versus non-wildfire period (0.39; 95%CI: 0.37, 0.42). Indoor PM2.5 concentrations and Finf varied substantially across household subgroups such as household income, age of the home, presence of air conditioning units, and use of portable air cleaners. ConclusionsIndoor PM2.5 was substantially higher during wildfire-impacted periods versus the rest of the study. Indoor PM2.5 and Finf were highly variable across households. Our results highlight potentially modifiable behaviors and characteristics that can be used in targeted intervention strategies.

A Review of Portable Air Cleaner Devices: Purification Processes, Performance Standards, and Effectiveness in Controlling Indoor Air Pollutants

Background and Objective: Indoor air pollutants are among the five most important environmental health risks. In recent years, concerns regarding indoor air quality in buildings have increased. This review has investigated studies conducted on portable air cleaners. Materials and Methods: After determining the keywords, conducting comprehensive searches in the internet databases, and taking into account the inclusion and exclusion criteria, a complete review was conducted to obtain the latest findings and the general trend of the studies. Results: Portable air cleaner devices are very diverse and are divided based on the type of technology used. Many standards have been developed to evaluate the performance of these devices in different countries, but none of them cover all aspects of performance. The effectiveness of these devices in removing VOCs is between 20% and 80%, depending on the type of technology and other influencing factors, and their effectiveness in removing suspended particles is between 70% and 95% on average. Furthermore, their efficiency in controlling COVID-19 is reported to be above 80% in cases where HEPA filters with grades 13 and above are used. Conclusion: Devices equipped with the HEPA filtration process have been found to be very effective in controlling indoor suspended particles. The use of devices equipped with UVGI, plasma, and ozone technologies should be accompanied by caution due to dangerous by-products.

Optimal location and performance prediction of portable air cleaner in composite room shapes using convolutional neural network

Portable air cleaners are commonly used to eliminate hazardous indoor air pollutants such as particulate matters and infectious viruses. The effectiveness of portable air cleaners heavily relies on their installation location, which affects the patterns of airflow carrying the pollutants. Herein, we propose a methodology for optimizing the portable air cleaner placement to maximize its effectiveness using artificial intelligence technology. To build an artificial intelligence model, we obtained the data on airflow patterns for different room shapes and locations of the portable air cleaner through numerical simulations. We utilized floor-plan image data to simplify the handling of complex geometric information related to portable air cleaner placements. The artificial intelligence model extracted geometric features from the floor plan and predicted the effectiveness of the portable air cleaner. The predicted results revealed that the model recommended the location with the highest effectiveness as optimal. The artificial intelligence model achieved a high prediction accuracy of 91.2% and precisely determined the optimal location in rooms with varying shapes. This approach can elucidate the complex relationship between geometric placements and airflow characteristics. Furthermore, the artificial intelligence model can be used as a powerful decision-making tool for indoor air quality management in the building environment.

The application of portable air cleaners in spaces occupied by vulnerable people during wildfire events.

In this study, PM2.5 concentrations were collected and documented during wildfire smoke impacted days using PurpleAir PA-II sensors at three different locations in a community located in the northwestern United States. Each location was comprised of three co-located sensors with one sensor positioned outdoors, one sensor indoors, and one sensor indoors with an air cleaner in the room. The relationship between both indoor and outdoor PM2.5 concentrations provided evidence on the effectiveness of sheltering indoors from wildfire smoke events with and without an air purification system.

Assessing the effectiveness of portable HEPA air cleaners for reducing particulate matter exposure in King County, Washington homeless shelters: Implications for community congregate settings

Over four thousand portable air cleaners (PACs) with high-efficiency particulate air (HEPA) filters were distributed by Public Health - Seattle & King County to homeless shelters during the COVID-19 pandemic. This study aimed to evaluate the real-world effectiveness of these HEPA PACs in reducing indoor particles and understand the factors that affect their use in homeless shelters. Four rooms across three homeless shelters with varying geographic locations and operating conditions were enrolled in this study. At each shelter, multiple PACs were deployed based on the room volume and PAC's clean air delivery rate rating. The energy consumption of these PACs was measured using energy data loggers at 1-min intervals to allow tracking of their use and fan speed for three two-week sampling rounds, separated by single-week gaps, between February and April 2022. Total optical particle number concentration (OPNC) was measured at 2-min intervals at multiple indoor locations and an outdoor ambient location. The empirical indoor and outdoor total OPNC were compared for each site. Additionally, linear mixed-effects regression models (LMERs) were used to assess the relationship between PAC use time and indoor/outdoor total OPNC ratios (I/OOPNC). Based on the LMER models, a 10 % increase in the hourly, daily, and total time PACs were used significantly reduced I/OOPNC by 0.034 [95 % CI: 0.028, 0.040; p < 0.001], 0.051 [95 % CI: 0.020, 0.078; p < 0.001], and 0.252 [95 % CI: 0.150, 0.328; p < 0.001], respectively, indicating that keeping PACs on resulted in significantly lower I/OOPNC. The survey suggested that keeping PACs on and running was the main challenge when operating them in shelters. These findings suggested that HEPA PACs were an effective short-term strategy to reduce indoor particle levels in community congregate living settings during non-wildfire seasons and the need for formulating practical guidance for using them in such an environment.

Standard precautions should include 'safe ventilation' to minimise far-afield airborne transmission in health and social care settings.

Standard precautions should include 'safe ventilation' to minimise far-afield airborne transmission in health and social care settings.

Effectiveness of a portable personal air cleaner in reducing the airborne transmission of respiratory pathogens

The airborne transmission in indoor environments represents the main pathway of respiratory pathogens, and most of the indoor environments do not have adequate ventilation to contain the risk of infection. This is particularly relevant for gathering spaces such as restaurants, schools, offices, etc. due to the long exposure times and high crowding levels.In this paper we investigated the effectiveness of a novel patented personal air cleaner in reducing the airborne transmission of respiratory pathogens both in close proximity (considering a typical face-to-face configuration at a conversational distance) and in shared indoor environments despite maintaining distancing (lecture room). The effectiveness of the portable protection device was investigated using complex transient 3D Computational Fluid Dynamics (CFD) numerical simulations. The mathematical model employed, validated through experimental measurements, is based on a Eulerian-Lagrangian approach, describing the air flow as the continuous phase and infectious respiratory particles as the discrete phase.The CFD analyses revealed that the air cleaner could strongly reduce the inhalation of respiratory pathogens in both the investigated scenarios. The air cleaner effectiveness in the case of a close proximity scenario, expressed as relative reduction of volume of infectious respiratory particles inhaled by the exposed subject, resulted >92%. In the case of use in a shared indoor environment, instead, during a 2-h lesson, the relative reduction of volume concentration of infectious particles in the breathing zone of the exposed subject was >99%.

Experimental study on the control effects of different strategies on particle transportation in a conference room: Mechanical ventilation, baffle, portable air cleaner, and desk air cleaner

To control the spread and transmission of airborne particles (especially SARS-CoV-2 coronavirus, recently) in the indoor environment, many control strategies have been employed. Comparisons of these strategies enable a reasonable choice for indoor environment control and cost-effectiveness. In this study, a series of experiments were conducted in a full-scale chamber to simulate a conference room. The control effects of four different strategies (a ventilation system (320 m3/h) with and without a baffle, a specific type of portable air cleaner (400 m3/h) and a specific type of desk air cleaner (DAC, 160 m3/h)) on the transportation of particles of different sizes were studied. In addition, the effects of coupling the ventilation strategies with five forms of indoor airflow organization (side supply and side or ceiling return, ceiling supply and ceiling or side return, floor supply and ceiling return) were evaluated. The cumulative exposure level (CEL) and infection probability were selected as evaluation indexes. The experimental results showed that among the four strategies, the best particle control effect was achieved by the PAC. The reduction in CEL for particles in the overall size range was 22.1% under the ventilation system without a baffle, 34.3% under the ventilation system with a baffle, 46.4% with the PAC, and 10.1% with the DAC. The average infection probabilities under the four control strategies were 11.3–11.8%, 11.1–11.8%, 9.1–9.5%, and 18.2–19.7%, respectively. Among the five different forms of airflow organization, the floor supply and ceiling return mode exhibited the best potential ability to remove particles.

The impact of automated control of indoor air pollutants on cardiopulmonary health, environmental comfort, sleep quality in a simulated apartment: A crossover experiment protocol

Air pollution makes an impact on cardio-pulmonary health. Since people spend over 90% of their time indoors, exposures to the indoor environment make the most significant impact on health. Among indoor sources, cooking emits the most particles that disperse through the residential indoor environment and expose occupants. We use fully controlled simulated residential modules to conduct exposure experiments. In the pilot study, participants stayed in modules for 1 week, and in the main study, 14 participants will stay in the module for 4 weeks. One module is operated as a classical US house air supply recommendation. The second module has an advanced control system that, alongside the standard air supply, activates air quality interventions: stove hood, portable air cleaners, bathroom exhaust and air flush (increasing air supply ∼3 times) as a function of the PM2.5 levels in the space. Environmental sensors based on Internet of Things technology simultaneously monitored Particulate Matter (PM2.5), CO2, Total Volatile Organic Compounds Relative Humidity and air temperature in all spaces and operated air quality interventions. Participant’s scheduled activities include morning and evening tasks, Monday through Friday. Participants may leave the module during the day. They will be asked to cook breakfast and dinner using lab-provided recipes. We measured each participant’s blood pressure, heart rate, and heart rate variability. Blood and urine samples were collected 3 times per participant in the pilot and will be collected 2 times a week in the main study. Up to 20 ml of blood and a minimum of 30 ml of urine will be sampled per collection. Analysis of blood and urine was performed for 8-hydroxy-2-deoxyguanosine (8-OHdG, urine), von Willebrand Factor (vWF, blood plasma), high sensitivity C-Reactive Protein (hsCRP, blood serum), Interleukin-6 (blood plasma), CD11b (blood), Fibrinogen (blood plasma), and Myeloperoxidase (blood serum). We conducted a Pilot for 2 weeks with 3 participants to test the study protocol and data collection. We adjusted the protocol for the main study based on the pilot results. Results showed that the proposed study protocol could be completed, and the methodology adopted in this study will provide valuable insights into the relationship between exposure to cooking particles and occupants' health.Trial registration: Mayo Clinic IRB 20-007908.

Strategies for reducing airborne disease transmission during breathing using a portable air cleaner in a classroom

In this work, computational fluid dynamics and a factorial study were conducted to analyze the air cleaning capabilities of a portable air cleaner (PAC) in a closed room with 10 thermal manikins and two air distribution system (ADS) speeds. The particles emitted by the breathing of the manikins (1250 particles/manikin) were tracked for 50 min, and their trajectories were analyzed. Factorial analysis was performed to investigate the relevance of the variables studied and their interactions. The results showed that the PAC–ADS configuration was a major factor affecting the transference of particles. A total risk index was defined (RItotal) to identify the total percentage of particles transferred between the occupants in each case. The best case had half the transference of particles compared with the worst case (2.03% vs 3.98%, respectively). Moreover, locating the PAC with a downward flow direction near the emitter significantly reduced the transference of its particles. However, it increased the number of particles that this emitter received from others in the classroom. The factorial analysis showed that PAC speed contributed the most to the transference of particles (24%) and particles filtered by the PAC (25.8%). In comparison, PAC position had the highest impact on particles remaining in the breathable zone of the room (13.7%) and particles leaving the system through the ADS (23.3%). Overall, a configuration in which the PAC is at the center of the classroom with a downward flow was shown to be the most efficient for reducing the spread of airborne diseases.

Use of portable air purifiers to reduce aerosols in hospital settings and cut down the clinical backlog.

SARS-CoV-2 has severely affected capacity in the National Health Service (NHS), and waiting lists are markedly increasing due to downtime of up to 50 min between patient consultations/procedures, to reduce the risk of infection. Ventilation accelerates this air cleaning, but retroactively installing built-in mechanical ventilation is often cost-prohibitive. We investigated the effect of using portable air cleaners (PAC), a low-energy and low-cost alternative, to reduce the concentration of aerosols in typical patient consultation/procedure environments. The experimental setup consisted of an aerosol generator, which mimicked the subject affected by SARS-CoV-19, and an aerosol detector, representing a subject who could potentially contract SARS-CoV-19. Experiments of aerosol dispersion and clearing were undertaken in situ in a variety of rooms with two different types of PAC in various combinations and positions. Correct use of PAC can reduce the clearance half-life of aerosols by 82% compared to the same indoor-environment without any ventilation, and at a broadly equivalent rate to built-in mechanical ventilation. In addition, the highest level of aerosol concentration measured when using PAC remains at least 46% lower than that when no mitigation is used, even if the PAC's operation is impeded due to placement under a table. The use of PAC leads to significant reductions in the level of aerosol concentration, associated with transmission of droplet-based airborne diseases. This could enable NHS departments to reduce the downtime between consultations/procedures.

A Pilot Study on the Combined Multi-domain Impact of Indoor Air Quality and Noise on Office Productivity

As people spend 90% of their time indoors, it was necessary to improve indoor environmental quality to enhance human productivity. Indoor environmental quality consists of indoor air quality (IAQ), thermal, visual, and acoustic comfort. However, only a few studies have investigated the combined effects of IAQ and noise. During and after the COVID-19 pandemic, portable air cleaner is often used in buildings to reduce the concentration of particles in the air, but it also generates noise. The objective of this study is to determine the effects of a portable air cleaner on IAQ and noise level, and more importantly the resulting combined effects on office productivity. For this purpose, we conducted human subject tests in an office and each test lasted for 1.5h. For each case, the air temperature, relative humidity, and supply airflow rate were kept constant while the air cleaner was switched between on and off for various noise levels and IAQ. We recruited 7 participants and collected data on the concentration of CO2, particles, and TVOC every 5 minutes. We used wristbands to measure heart rate and skin electrodermal activity. And we used headbands to measure electroencephalogram (EEG) and facial activity. The questionnaire survey was used to learn the occupants’ responses to the indoor environment. To learn their productivity, occupants also did math addition tasks and typing tasks. We found that when using the portable air cleaner, the noise level raised from 55dB to around 70dB. The particle and TVOC concentrations were reduced by 90% and 20%, respectively. The questionnaire survey showed that the occupants felt unsatisfied due to noise. And the noise dissatisfaction exceeded the improved IAQ. By analyzing the EEG and the number of jaw clenches, the occupants felt more nervous and concentrated when the air cleaner was on. We confirmed the impact of noise and the combined impact of IAQ and noise on office productivity.

Pulsating jet ventilation add-ons performance for reducing the contaminant spread in classrooms: Portable air cleaners vs. upper room UVGI

This paper examines the extent to which “add-on” cleaning devices in a classroom ventilated with a pulsating jet ventilation (PJV) system are able to reduce the contaminant spread risks between students when one of them is infected. Two types of “add-on” devices are investigated: portable air cleaners (PACs) and upper room ultraviolet germicidal irradiation (UR-UVGI) lamps. The cleaning effectiveness of each system is evaluated by comparing the contaminant concentration reduction ratio (CR) within the breathing layer in each group of students and the intake fraction (iF) with their corresponding values of standalone PJV operation under the same conditions. Detailed 3D computational fluid dynamic (CFD) models were developed and validated against published experimental data. A parametric analysis was performed by varying the PJV supply flowrate and its period of intermittency to establish the PJV operating conditions that maximize the cleaning and protection effectiveness of each “add-on” device at acceptable thermal comfort and CO2 levels.It was found that for maximum cleaning effectiveness, the PJV system is recommended to operate with an UR-UVGI system at supply flowrate between 250 l/s and 350 l/s with a range of intermittency periods between 4 min and 5 min. However, for a maximum protection against cross-contamination, the PJV system should operate with PAC devices at 400 m3/h for PJV flowrate ranging between 250 l/s and 350 l/s irrespective of the intermittency period with iFmax values between 1.47×10−4 and 0.67×10−4. The addition of “add-ons” resulted in a maximum of 7% increase in the overall energy consumption.

Evaluation of Interventions to Improve Ventilation in Households to Reduce Risk for Transmission of Severe Acute Respiratory Syndrome Coronavirus 2.

Inadequate ventilation may contribute to the high risk for household transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). We evaluated the effectiveness of several interventions recommended to improve ventilation in households. In 7 residential homes, carbon dioxide monitoring was conducted to assess ventilation in occupied open areas such as family rooms and in bedrooms and/or offices. Carbon dioxide levels above 800 parts per million (ppm) were considered an indicator of suboptimal ventilation for the number of people present. In 1 of the 7 homes, various interventions to improve ventilation or to filter air were assessed in a kitchen area by measuring clearance of aerosol particles produced using an aerosol-based spray system and carbon dioxide generated by cooking with a gas stove. Carbon dioxide levels rose above 800 ppm in bedrooms and offices with 2 occupants when windows and doors were closed and in open areas during gatherings of 5 to 10 people; carbon dioxide levels decreased when windows or doors were opened. Clearance of carbon dioxide and aerosol particles significantly increased with interventions including running fans, operating portable air cleaners, and opening windows, particularly when there was a noticeable breeze or when a window fan was used to blow contaminated air outside. In households, several measures to improve ventilation or air filtration were effective in reducing carbon dioxide accumulation or enhancing clearance of carbon dioxide and aerosol particles. Studies are needed to determine if interventions to improve ventilation can reduce the risk for airborne transmission of SARS-CoV-2 in households.

Optimizing air purification for household particulate matters using sensor-based and time-based intervention strategies

Filtration efficiency of portable air cleaner (PAC) is affected by resident perceptions and adherences to when and how to operate the PAC. Incorporating PAC with smart control and sensor technology holds the promise to effectively reduce indoor air pollutants. This study aims to evaluate the efficiency of a PAC at removing indoor fine particulate matters (PM2.5) exposure under two automated operation settings: (1) a time-based mode in which the operation time is determined based on perceived time periods of indoor pollution by residents; (2) a sensor-based mode in which an air sensor monitor is used to determine the PAC based on the actual PM2.5 level against the indoor air quality guideline. The study was conducted in a residential room for 55 days with a rolling setting on PAC (no filtration, sensor-based, time-based filtrations) and a continuous measurement of PM2.5. We found that the PAC operated with sensor-based mode removed PM2.5 concentrations by 47% and prolonged clean air (<35 μg/m3) period by 23% compared to the purifications with time-based mode which reduced PM2.5 by 29% and increased clean air period by 13%. The sensor-based filtration identified indoor pollution episodes that are hardly detected by personal perceptions. Our study findings support an automated sensor-based approach to optimize the use of PAC for effectively reducing indoor PM2.5 exposure.

Impact of do-it-yourself air cleaner design on the reduction of simulated wildfire smoke in a controlled chamber environment.

During wildfire smoke events public health agencies release advisories to stay indoors, close doors and windows, and operate a portable air cleaner (PAC). The do-it-yourself (DIY) air cleaner consisting of a box fan and a furnace filter is a widely used low-cost alternative to commercial PACs because of its increased accessibility. In this study, we evaluate the clean air delivery rate (CADR) of different DIY air cleaner designs for reducing simulated wildfire smoke and identify operating parameters that may impact their performance and use. The simplest formulation of a DIY air cleaner (box fan with taped on minimum effectiveness reporting value - [MERV] 13 furnace filter) had a CADR of 111.2± 1.3ft3 /min (CFM). Increasing the fan flow by changing the fan type, increasing the fan setting, or reducing the pressure drop across the filtering surface increased the CADR. Large increases in CADR could be obtained by using a shroud (40%), using a 4″ thick filter (123%) using two filters in a wedge shape (137%), or using four filters in a Corsi-Rosenthal (CR) box design (261%). The CADR was greatly reduced with filters heavily loaded with smoke, pointing to the need for frequent filter changes during smoke events.

Impact of Do-It-Yourself and Commercial Air Cleaner Usage on Health and Residential PM2.5

Background and aim: Wildfire smoke can threaten health, necessitating creating cleaner indoor air spaces. Commercially available portable air cleaners (PACs) mitigate smoke impacts indoors but can be expensive or inaccessible. Lower-cost Do-It-Yourself (DIY) PACs (furnace filter attached to box fan) offer an affordable alternative. However, evidence of their effectiveness in real-world settings is limited. This pilot study aimed to 1) evaluate the effect of DIY/commercial PAC usage on indoor PM2.5 and health outcomes during wildfire season among tribal community members in Hoopa, California and 2) assess barriers and facilitators to use of either intervention. Methods: During four one-to-two-week phases (baseline; DIY PAC usage &amp;#x2265;8 hours/day; commercial PAC usage &amp;#x2265;8 hours/day; and air sensor with visual display with optional PAC use), we monitored indoor and outdoor PM2.5 at participants’ homes. We conducted phase-specific phone surveys about participants’ health, behaviors, and perceptions. We analyzed indoor PM2.5 and health outcomes associated with PAC usage using mixed effects multivariate linear regression and tabulated behavioral responses. Results: DIY and commercial PAC usage was significantly associated with reduced infiltrated PM2.5 (n=6). High usage (&amp;#x2265;30% of phase) of either PAC was significantly associated with improved health (measured as a composite score), relative to low usage (&amp;#x3c;10% of phase) (n=10). Noise was the primary barrier to DIY PAC use, while quiet operation and small size of commercial PACs facilitated use. Nonetheless, eight of nine participants who preferred commercial PACs said they would use DIY PACs if the air were very smoky. Conclusions: DIY and commercial PACs were associated with improved indoor PM2.5 and health, but the loudness of DIY PACs hindered use. State, local, and tribal organizations should consider these conclusions in tailoring messaging and allocating resources in preparation for wildfire seasons. Disclaimer: Does not reflect EPA views or policy. Keywords: Indigenous, wildfire smoke, indoor air quality

Efficacy of HEPA Air Cleaner on Improving Indoor Particulate Matter 2.5 Concentration.

High-efficiency particulate air (HEPA) filters is a potential tool used to remove fine particles and improve indoor air quality. This study aims to analyze the real-world efficacy of portable HEPA air cleaners in a household environment. Laser light dispersion PM2.5 sensors are used to continuously monitor the indoor and outdoor PM2.5 level before and after HEPA air cleaner filtration. Overall, HEPA air cleaners significantly reduce the indoor PM2.5 level (33.5 ± 10.3 vs. 17.2 ± 10.7 µg/m3, mean difference (MD) = −16.3 µg/m3, p < 0.001) and indoor/outdoor PM2.5% (76.3 ± 16.8 vs. 38.6 ± 19.8%, MD = −37.7%, p < 0.001). The efficacy to reduce PM2.5 is strongest in three machines with medium-flow setting group (indoor PM2.5 MD: −26.5 µg/m3, indoor/outdoor PM2.5 percentage MD: −56.4%). Multiple linear regression demonstrates that outdoor PM2.5, machine number, airflow speed, and window ventilation are significant factors associated with indoor PM2.5 concentrations (R = 0.879) and percentage of the indoor/outdoor PM2.5 ratio (R = 0.808). HEPA air cleaners can effectively improve indoor PM2.5 air pollution. Adequate air cleaner machine numbers, appropriate airflow, and window ventilation limitations are important to achieve the best efficacy of the HEPA air cleaner.

HEPA filters of portable air cleaners as a tool for the surveillance of SARS-CoV-2.

Studies about the identification of SARS‐CoV‐2 in indoor aerosols have been conducted in hospital patient rooms and to a lesser extent in nonhealthcare environments. In these studies, people were already infected with SARS‐CoV‐2. However, in the present study, we investigated the presence of SARS‐CoV‐2 in HEPA filters housed in portable air cleaners (PACs) located in places with apparently healthy people to prevent possible outbreaks. A method for detecting the presence of SARS‐CoV‐2 RNA in HEPA filters was developed and validated. The study was conducted for 13 weeks in three indoor environments: school, nursery, and a household of a social health center, all in Ciudad Real, Spain. The environmental monitoring of the presence of SARS‐CoV‐2 was conducted in HEPA filters and other surfaces of these indoor spaces for a selective screening in asymptomatic population groups. The objective was to limit outbreaks at an early stage. One HEPA filter tested positive in the social health center. After analysis by RT‐PCR of SARS‐CoV‐2 in residents and healthcare workers, one worker tested positive. Therefore, this study provides direct evidence of virus‐containing aerosols trapped in HEPA filters and the possibility of using these PACs for environmental monitoring of SARS‐CoV‐2 while they remove airborne aerosols and trap the virus.

Portable air cleaner use and biomarkers of inflammation: A systematic review and meta-analysis

Fine particulate matter air pollution (PM2.5) is a major contributor to cardiovascular morbidity and mortality, potentially via increased inflammation. PM2.5 exposure increases inflammatory biomarkers linked to cardiovascular disease, including CRP, IL-6 and TNFα. Portable air cleaners (PACs) reduce individual PM2.5 exposure but evidence is limited regarding whether PACs also reduce inflammatory biomarkers. We performed a systematic review and meta-analysis of trials evaluating the use of PACs to reduce PM2.5 exposure and inflammatory biomarker concentrations. We identified English-language articles of randomized sham-controlled trials evaluating high efficiency particulate air filters in non-smoking, residential settings measuring serum CRP, IL-6 and TNFα before and after active versus sham filtration, and performed meta-analysis on the extracted modeled percent change in biomarker concentration across studies. Of 487 articles identified, we analyzed 14 studies enrolling 778 participants that met inclusion criteria. These studies showed PACs reduced PM2.5 by 61.5 % on average. Of the 14 included studies, 10 reported CRP concentrations in 570 participants; these showed active PAC use was associated with 7 % lower CRP (95 % CI: −14 % to 0.0 %, p = 0.05). Nine studies of IL-6, with 379 participants, showed active PAC use was associated with 13 % lower IL-6 (95 % CI: [−23 %, −3 %], p = 0.009). Six studies, with 269 participants, reported TNF-α and demonstrated no statistical evidence of difference between active and sham PAC use. Portable air cleaners that reduce PM2.5 exposure can decrease concentrations of inflammatory biomarkers associated with cardiovascular disease. Additional studies are needed to evaluate clinical outcomes and other biomarkers.