Evaluation of fixed and adaptive concentration thresholds for particle filter systems.

Particle filtration can effectively reduce indoor concentrations of particulate matter (PM) but may incur high energy use. This study evaluates fixed and adaptive concentration thresholds to automate the operation of filtration systems. Simulated environments were derived from week-long continuous PM measurements from Dylos DC1700 (N = 104) and Alphasense OPC-N2 (N = 100) particle counters deployed in apartments in Toronto. A fixed threshold of 4.0 µg·m-3 resulted in a mean air cleaner runtime of 6.9%-21.0% depending on clean air delivery rate (CADR) and particle sensor, while providing mean concentration reductions of 67%-71% compared to operating the air cleaner constantly (runtime = 100%). In most environments, runtime could be further reduced by raising the fixed threshold while resulting in only a modest decrease in absolute and normalized mean exposure reduction. Using an adaptive threshold derived from a k-means clustering approach generally provided substantial exposure reduction while preventing high runtimes. These results were generally insensitive to cleaning power and the monitor used to measure particle concentrations. Reducing the energy usage of particle filter systems will make them a more viable and sustainable means of improving occupant health.

Assessing the use of portable air cleaners for reducing exposure to airborne diseases in a conference room with thermal stratification.

The COVID-19 pandemic has highlighted the need for strategies that mitigate the risk of aerosol disease transmission in indoor environments with different ventilation strategies. It is necessary for building operators to be able to estimate and compare the relative impacts of different mitigation strategies to determine suitable strategies for a particular situation. Using a validated CFD model, this study simulates the dispersion of exhaled contaminants in a thermally stratified conference room with overhead heating. The impacts of portable air-cleaners (PACs) on the room airflow and contaminant distribution were evaluated for different PAC locations and flow rates, as well as for different room setups (socially distanced or fully occupied). To obtain a holistic view of a strategy's impacts under different release scenarios, we simultaneously model the steady-state distribution of aerosolized virus contaminants from eight distinct sources in 18 cases for a total of 144 release scenarios. The simulations show that the location of the source, the PAC settings, and the room set-up can impact the average exposure and PAC effectiveness. For this studied case, the PACs reduced the room average exposure by 31%-66% relative to the baseline case. Some occupant locations were shown to have a higher-than-average exposure, particularly those seated near the airflow outlet, and occupants closest to sources tended to see the highest exposure from said source. We found that these PACs were effective at reducing the stratification caused by overhead heating, and also identified at least one sub-optimal location for placing a PAC in this space.

Real-time measurements of PM2.5 and ozone to assess the effectiveness of residential indoor air filtration in Shanghai homes.

Portable air cleaners are increasingly used in polluted areas in an attempt to reduce human exposure; however, there has been limited work characterizing their effectiveness at reducing exposure. With this in mind, we recruited forty-three children with asthma from suburban Shanghai and deployed air cleaners (with HEPA and activated carbon filters) in their bedrooms. During both 2-week filtration and non-filtration periods, low-cost PM2.5 and O3 air monitors were used to measure pollutants indoors, outdoors, and for personal exposure. Indoor PM2.5 concentrations were reduced substantially with the use of air cleaners, from 34 ± 17 to 10 ± 8 µg/m3 , with roughly 80% of indoor PM2.5 estimated to come from outdoor sources. Personal exposure to PM2.5 was reduced from 40 ± 17 to 25 ± 14 µg/m3 . The more modest reductions in personal exposure and high contribution of outdoor PM2.5 to indoor concentrations highlight the need to reduce outdoor PM2.5 and/or to clean indoor air in multiple locations. Indoor O3 concentrations were generally low (mean = 8±4 ppb), and no significant difference was seen by filtration status. The concentrations of pollutants and the air cleaner effectiveness were highly variable over time and across homes, highlighting the usefulness of real-time air monitors for understanding individual exposure reduction strategies.

Energy consumption of using HEPA-based portable air cleaner in residences: A monitoring study in Seattle, US.

Portable air cleaners (PACs), offering both auto and manual (adjustable) operation modes, are commonly used in residences. Compared with adjustable mode, auto mode's advantage of reducing indoor PM2.5 has been previously demonstrated. This study examines the energy consumption of such PACs in six residences recruited in Seattle, United States, and compares the power consumption between auto and adjustable modes. Each residence went through a one-week-long PAC filtration session under auto and adjustable modes, respectively. PAC power consumption, indoor PM2.5, temperature, and relative humidity (RH) were measured at 10-second intervals in each residence. A linear mixed-effects regression (LMER) model was used to compare the PAC power consumption between the two modes after adjusting for indoor PM2.5, temperature, and RH. Results show that the mean (standard deviation) PAC power consumption under adjustable and auto modes were 7.0 (3.5) and 6.8 (2.6) W, respectively. The average monthly energy consumption of continuous PAC operation was estimated to be ~5 kWh for both modes. Based on the LEMR model, PAC power consumption under auto mode was approximately 3% larger than that under adjustable mode, after adjusting for living-room PM2.5, temperature, and RH levels. The implications for PAC operation mode selection in residential environments were discussed.

Residential cooking-related PM2.5: Spatial-temporal variations under various intervention scenarios.

Some cooking events can generate high levels of hazardous PM2.5. This study assesses the dispersion of cooking-related PM2.5 throughout a naturally-ventilated apartment in the US, examines the dynamic process of cooking-related emissions, and demonstrates the impact of different indoor PM2.5 mitigating strategies. We conducted experiments with a standardized pan-frying cooking procedure under seven scenarios, involving opening kitchen windows, using a range hood, and utilizing a portable air cleaner (PAC) in various indoor locations. Real-time PM2.5 concentrations were measured in the open kitchen, living room, bedroom (door closed), and outdoor environments. Decay-related parameters were estimated, and time-resolved PM2.5 emission rates for each experiment were determined using a dynamic model. Results show that the 1-min mean PM2.5 concentrations in the kitchen and living room peaked 1-7 min after cooking at levels of 200-1400 µg/m3, which were more than 9 times higher than the peak bedroom levels. Mean (standard deviation) kt for the kitchen, ranging from 0.58 (0.02) to 6.62 (0.34) h-1, was generally comparable to that of the living room (relative difference < 20%), but was 1-5 times larger than that of the bedroom. The range of PM2.5 full-decay time was between 1-10 h for the kitchen and living room, and from 0 to > 6 h for the bedroom. The PM2.5 emission rates during and 5 min after cooking were 2.3 (3.4) and 5.1 (3.9) mg/min, respectively. Intervention strategies, including opening kitchen windows and using PACs either in the kitchen or living room, can substantially reduce indoor PM2.5 levels and the related full-decay time. For scenarios involving a PAC, placing it in the kitchen (closer to the source) resulted in better efficacy.

Primary and secondary consequences of indoor air cleaners.

Air cleaning is broadly applied to reduce contaminant concentrations in many buildings. Although diverse in underlying technology, mode of application, target contaminants, and effectiveness, there are also commonalities in the framework for understanding their primary impact (i.e. concentration reductions) and secondary impacts (e.g. energy use and by-product production). Furthermore, both primary and secondary impacts are moderated by the specific indoor context in which an air cleaner is used. This investigation explores the dynamics of removal efficiency in a variety of air cleaners and combines efficiency and flow rate to put air cleaning in the context of real indoor environments. This allows for the direct comparison to other indoor pollutant loss mechanisms (ventilation and deposition) and further suggests that effective air cleaner use is context and contaminant specific. The concentration reduction impacts of air cleaning need to be contrasted with the secondary consequences that arise from the use of air cleaners. This study emphasizes two important secondary consequences: energy use of the air cleaning process and primary and secondary emissions from air cleaners. This study also identifies current research challenges and areas for large leaps in our understanding of the role of air cleaners in improving indoor environmental quality.

Experimental and Modeled Assessment of Interventions to Reduce PM2.5 in a Residence during a Wildfire Event.

Increasingly large and frequent wildfires affect air quality even indoors by emitting and dispersing fine/ultrafine particulate matter known to pose health risks to residents. With this health threat, we are working to help the building science community develop simplified tools that may be used to estimate impacts to large numbers of homes based on high-level housing characteristics. In addition to reviewing literature sources, we performed an experiment to evaluate interventions to mitigate degraded indoor air quality. We instrumented one residence for one week during an extreme wildfire event in the Pacific Northwest. Outdoor ambient concentrations of PM2.5 reached historic levels, sustained at over 200 µg/m3 for multiple days. Outdoor and indoor PM2.5 were monitored, and data regarding building characteristics, infiltration, and mechanical system operation were gathered to be consistent with the type of information commonly known for residential energy models. Two conditions were studied: a high-capture minimum efficiency rated value (MERV 13) filter integrated into a central forced air (CFA) system, and a CFA with MERV 13 filtration operating with a portable air cleaner (PAC). With intermittent CFA operation and no PAC, indoor corrected concentrations of PM2.5 reached 280 µg/m3, and indoor/outdoor (I/O) ratios reached a mean of 0.55. The measured I/O ratio was reduced to a mean of 0.22 when both intermittent CFA and the PAC were in operation. Data gathered from the test home were used in a modeling exercise to assess expected I/O ratios from both interventions. The mean modeled I/O ratio for the CFA with an MERV 13 filter was 0.48, and 0.28 when the PAC was added. The model overpredicted the MERV 13 performance and underpredicted the CFA with an MERV 13 filter plus a PAC, though both conditions were predicted within 0.15 standard deviation. The results illustrate the ways that models can be used to estimate indoor PM2.5 concentrations in residences during extreme wildfire smoke events.

Real-World Effectiveness of Portable Air Cleaners in Reducing Home Particulate Matter Concentrations.

Portable air cleaners (PACs) equipped with HEPA filters are gaining attention as cost-effective means of decreasing indoor particulate matter (PM) air pollutants and airborne viruses. However, the performance of PACs in naturalistic settings and spaces beyond the room containing the PAC is not well characterized. We conducted a single-blinded randomized cross-over interventional study between November 2020 and May 2021 in the homes of adults who tested positive for COVID-19. The intervention was air filtration with PAC operated with the HEPA filter set installed ("filter" condition) versus removed ("sham" condition, i.e., control). Sampling was performed in 29 homes for two consecutive 24-hour periods in the primary room (containing the PAC) and a secondary room. PAC effectiveness, calculated as reductions in overall mean PM2.5 and PM10 concentrations during the filter condition, were for the primary rooms 78.8% and 63.9% (n = 23), respectively, and for the secondary rooms 57.9% and 60.4% (n = 22), respectively. When a central air handler (CAH) was reported to be in use, filter-associated reductions of PM were statistically significant during the day (06:00-22:00) and night (22:01-05:59) in the primary rooms but only during the day in the secondary rooms. Our study adds to the literature evaluating the real-world effects of PACs on a secondary room and considering the impact of central air systems on PAC performance.

Portable Air Cleaner Usage and Particulate Matter Exposure Reduction in an Environmental Justice Community: A Pilot Study.

Particulate matter (PM) exposure is associated with adverse health outcomes, including respiratory illness. A large fraction of exposure to airborne contaminants occurs in the home. This study, conducted over 5 months in a community with high asthma rates (Chelsea, MA, USA), investigated the use of portable air cleaners (PACs) to reduce indoor PM. Seven asthma-affected households participated, receiving a PAC (Austin Air Health Mate HEPA filter), a QuantAQ sensor to measure PM1, PM2.5, PM10 (µg/m3), and a HOBO plug-load data logger to track PAC usage. Results describe hourly and daily PM concentrations and PAC usage for each household. Hourly average PM concentrations decreased when PACs were turned on (vs. when they were turned off) across households during the study period: PM1 decreased by 0.46 µg/m3, PM2.5 decreased by 0.69 µg/m3, and PM10 decreased by 3.22 µg/m3. PAC usage varied for each household, including constant usage in one household and only usage at certain times of day in others. Higher filtration settings led to lower PM, with significant reductions in some, but not all, homes. Our findings highlight some difficulties in implementing household PAC interventions, yet also provide evidence to support household-level interventions to reduce PM and other indoor sources of air pollution. We also highlight academic-community partnerships as contributing to evidence-based solutions.

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.

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.

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.

The effect of using personal-level indoor air cleaners and respirators on biomarkers of cardiorespiratory health: a systematic review.

BACKGROUND: Emerging studies have investigated potential cardiovascular and respiratory health impacts from the use of personal-level intervention equipment against air pollution exposure. The objective of this systematic review is to assess the efficacy of personal-level air pollution intervention on mitigating adverse health effects from air pollution exposure by using portable air cleaner or wearing respirator. METHODS: In this systematic review, we searched PubMed and Web of Science for published literatures up to May 31, 2020, focusing on personal-level air pollution intervention studies. Among these studies, we investigated the impacts on cardio-respiratory responses to the use of these interventions. The intervention of review interest was the use of personal-level equipment against air pollution, including using portable air cleaner indoors or wearing respirator outdoors. The outcome of review interest was impacts on cardio-respiratory health endpoints following interventions, including level changes in blood pressure, heart rate variability (HRV), lung function, and biomarkers of inflammation and oxidative stress. Weighted mean differences or percent changes were pooled in meta-analyses for these health endpoints. The heterogeneity across studies was assessed using the Cochran's Q-statistic test, and the individual study quality was assessed using the Cochrane risk of bias tool version 2 (RoB 2). We further applied the Grading of Recommendations Assessment, Development, and Evaluation (GRADE) method to evaluate the certainty of evidence. RESULTS: From systematic literature search and screening, we identified 29 related eligible intervention studies, including 21 studies on indoor portable air cleaner use and 8 studies on respirator use. For portable air cleaner intervention, we observed suggestive evidence of beneficial changes on cardio-respiratory health endpoints. Collectively in these studies, we found significantly beneficial changes of 2.01% decreases (95% CI: 0.50%, 3.52%) in systolic blood pressure, as well as non-significantly beneficial changes of 3.04% increases (95% CI: -2.65%, 8.74%) in reactive hyperemia index and 0.24% increases (95% CI: -0.82%, 1.31%) in forced expiratory volume in 1 s. We also observed non-significant reductions in levels of inflammation and oxidative stress biomarkers, including C-reactive protein, interleukin-6, fibrinogen, fractional exhaled nitric oxide and malondialdehyde. For respirator intervention, we observed some beneficial changes on cardiovascular health endpoints, such as significant increases in HRV parameters [SDNN (2.20%, 95% CI: 0.54%, 3.86%)], as well as non-significant decreases in blood pressure [SBP (0.63 mmHg, 95% CI: -0.39, 1.66)]; however, no sufficient data were available for meta-analyses on lung function and biomarkers. RoB 2 assessments suggested that most intervention studies were with a moderate to high overall risk of bias. The certainty of evidence for intervention outcome pairs was graded very low for either portable air cleaner or respirator intervention. The common reasons to downgrade study evidence included loss to follow-up, lack of blinding, lack of washout period, small sample size, and high heterogeneity across studies. CONCLUSIONS: The uses of indoor portable air cleaner and respirator could contribute to some beneficial changes on cardiovascular health, but with much limited evidence on respiratory health. Low certainty of the overall study evidence shed light on future research for larger sample size trials with more rigorous study design.

Is hydrogen peroxide an effective mouthwash for reducing the viral load of SARS-CoV-2 in dental clinics?

BACKGROUND: Previous studies have demonstrated that SARS-CoV-2 is mainly transmitted by inhalation of aerosols and can remain viable in the air for hours. Viruses can spread in dental settings and put professionals and patients at high risk of infection due to proximity and aerosol-generating procedures, and poor air ventilation. OBJECTIVES: The aim of this study was to investigate the effects of a 1% hydrogen peroxide (H2O2) mouth rinse on reducing the intraoral SARS-CoV-2 load. METHODS: Portable air cleaners with HEPA filters exposed for 3 months were analysed to test for virus presence in a waiting room (where patients wore a face mask but did not undergo mouth rinsing) and three treatment rooms (where patients wore no mask but carried out mouth rinsing). As CO2 is co-exhaled with aerosols containing SARS-CoV-2 by COVID-19 infected people, we also measured CO2 as a proxy of infection risk indoors. Specific primer and probe RT-PCR were applied to detect viral genomes of the SARS-CoV-2 virus in the filters. Specifically, we amplified the nucleocapsid gene (Nuclv) of SARS-CoV-2. RESULTS: CO2 levels ranged from 860 to 907 ppm, thus indicating low ventilation and the risk of COVID-19 transmission. However, we only found viral load in filters from the waiting room and not from the treatment rooms. The results revealed the efficiency of 1-minute mouth rinsing with 1% H2O2 since patients rinsed their mouths immediately after removing their mask in the treatment rooms. CONCLUSIONS: Our findings suggest that dental clinics would be safer and more COVID-19 free by implementing mouth rinsing 1 min with 1% H2O2 immediately after the patients arrive at the clinic.

Effects of mechanical ventilation and portable air cleaner on aerosol removal from dental treatment rooms.

OBJECTIVES: To evaluate the mechanical ventilation rates of dental treatment rooms and assess the effectiveness of aerosol removal by mechanical ventilation and a portable air cleaner (PAC) with a high-efficiency particulate air (HEPA) filter. METHODS: Volumetric airflow were measured to assess air change rate per hour by ventilation (ACHvent). Equivalent ventilation provided by the PAC (ACHpac) was calculated based on its clean air delivery rate. Concentrations of 0.3, 0.5 and 1.0 µm aerosol particles were measured in 10 dental treatment rooms with various ventilation rates at baseline, after 5-min of incense burn, and after 30-min of observation with and without the PAC or ventilation system in operation. Velocities of aerosol removal were assessed by concentration decay constants for the 0.3 µm particles with ventilation alone (Kn) and with ventilation and PAC (Kn+pac), and by times needed to reach 95 % and 100 % removal of accumulated aerosol particles. RESULTS: ACHvent varied from 3 to 45. Kn and Kn+pac were correlated with ACHvent (r = 0.90) and combined ACHtotal (r = 0.81), respectively. Accumulated aerosol particles could not be removed by ventilation alone within 30-min in rooms with ACHvent<15. PAC reduced aerosol accumulation and accelerated aerosol removal, and accumulated aerosols could be completely removed in 4 to 12-min by ventilation combined with PAC. Effectiveness of the PAC was especially prominent in rooms with poor ventilation. Added benefit of PAC in aerosol removal was inversely correlated with ACHvent. CONCLUSIONS: Aerosol accumulation may occur in dental treatment rooms with poor ventilation. Addition of PAC with a HEPA filter significantly reduced aerosol accumulation and accelerated aerosol removal. CLINICAL SIGNIFICANCE: Addition of PAC with a HEPA filter improves aerosol removal in rooms with low ventilation rates.

Characterization of cooking-related ultrafine particles in a US residence and impacts of various intervention strategies.

Interventions that improve air exchange or filter the air have the potential to reduce particle exposures from residential cooking. In this study, we evaluated the effect of using a range hood, opening kitchen windows, and using portable air cleaners (PACs) in various home locations on the concentrations of ultrafine particles (UFPs) at different times and in different rooms during and after cooking. All experiments were conducted using a standardized cooking protocol in a real-world naturally-ventilated apartment located in the northwest United States. Real-time UFP measurements collected from the kitchen, living room, and bedroom locations were used to estimate parameters of a dynamic model, which included time-varying particle emission rates from cooking and particle decay. We found that 1-min mean UFP number concentrations in the kitchen and living room mostly peaked within 0-10 min after cooking ended at levels of 150,000-500,000 particles/cm3. In contrast, the bedroom UFP concentrations were consistently low except for the window-open scenario. While varying considerably with time, the 1-min UFP emission rates were comparable during and within 5-min after cooking, with means (standard deviations) of 0.8 (1.1) × 1012 and 1.1 (1.2) × 1012 particles/min, respectively. Compared with the no-intervention scenario, keeping the kitchen windows open and using a kitchen range hood reduced the mean indoor average UFP concentrations during and 1 h after cooking by ~70% and ~35%, respectively. Along with the range hood on, utilizing a PAC in the kitchen during and after cooking further reduced the mean indoor average UFP levels during and 1 h after cooking by an additional 53%. In contrast, placing the PAC in the living room or bedroom resulted in worse efficacy, with additional 2-13% reductions. These findings provide useful information on how to reduce cooking-related UFP exposure via readily accessible intervention strategies.

Field measurements of PM2.5 infiltration factor and portable air cleaner effectiveness during wildfire episodes in US residences.

Wildfires have frequently occurred in the western United States (US) during the summer and fall seasons in recent years. This study measures the PM2.5 infiltration factor in seven residences recruited from five dense communities in Seattle, Washington, during a 2020 wildfire episode and evaluates the impacts of HEPA-based portable air cleaner (PAC) use on reducing indoor PM2.5 levels. All residences with windows closed went through an 18-to-24-h no filtration session, with five of seven following that period with an 18-to-24-h filtration session. Auto-mode PACs, which automatically adjust the fan speed based on the surrounding PM2.5 levels, were used for the filtration session. 10-s resolved indoor PM2.5 levels were measured in each residence's living room, while hourly outdoor levels were collected from the nearest governmental air quality monitoring station to each residence. Additionally, a time-activity diary in minute resolution was collected from each household. With the impacts of indoor sources excluded, indoor PM2.5 mass balance models were developed to estimate the PM2.5 indoor/outdoor (I/O) ratios, PAC effectiveness, and decay-related parameters. Among the seven residences, the mean infiltration factor ranged from 0.33 (standard deviation [SD]: 0.06) to 0.76 (SD: 0.05). The use of auto-mode PAC led to a 48%-78% decrease of indoor PM2.5 levels after adjusting for outdoor PM2.5 levels and indoor sources. The mean (SD) air exchange rates ranged from 0.30 (0.13) h-1 to 1.41 (3.18) h-1 while the PM2.5 deposition rate ranged from 0.10 (0.54) h-1 to 0.49 (0.47) h-1. These findings suggest that staying indoors, a common protective measure during wildfire episodes, is insufficient to prevent people's excess exposure to wildfire smoke, and provides quantitative evidence to support the utilization of auto-mode PACs during wildfire events in the US.

Mitigation of indoor human exposure to airborne particles of outdoor origin in an urban environment during haze and non-haze periods.

During the 2019 smoke haze episode in Singapore, elevated levels of fine particulate matter (PM2.5) were observed, deteriorating both ambient and indoor air quality (IAQ). We investigated the mitigation of indoor human exposure to PM2.5 of outdoor origin under diverse exposure scenarios with and without filtration of PM2.5 during both hazy and non-hazy days. The key objective of our study was to make a comparative evaluation of the effectiveness of portable air cleaners (PACs) and air conditioning (AC) systems equipped with particle filters in improving IAQ and to assess related long-term carcinogenic and non-carcinogenic health risks. We conducted real-time measurements of PM2.5, black carbon mass concentrations and particle number concentrations in both indoor and outdoor areas, quantified the relative concentrations of the water-soluble fraction of toxic trace elements in PM2.5 for health risk assessment, and estimated the levels of thermal comfort. In addition, we calculated the total estimated cost of indoor air pollution control. Our findings suggest that indoor air cleaners are more effective at mitigating human exposure to airborne particles and reducing health risk with less consumption of electricity and better cost-effectiveness compared to AC. This information would be beneficial for public health interventions during major air pollution events.

Cardiopulmonary Impact of Particulate Air Pollution in High-Risk Populations: JACC State-of-the-Art Review.

Fine particulate air pollution <2.5 µm in diameter (PM2.5) is a major environmental threat to global public health. Multiple national and international medical and governmental organizations have recognized PM2.5 as a risk factor for cardiopulmonary diseases. A growing body of evidence indicates that several personal-level approaches that reduce exposures to PM2.5 can lead to improvements in health endpoints. Novel and forward-thinking strategies including randomized clinical trials are important to validate key aspects (e.g., feasibility, efficacy, health benefits, risks, burden, costs) of the various protective interventions, in particular among real-world susceptible and vulnerable populations. This paper summarizes the discussions and conclusions from an expert workshop, Reducing the Cardiopulmonary Impact of Particulate Matter Air Pollution in High Risk Populations, held on May 29 to 30, 2019, and convened by the National Institutes of Health, the U.S. Environmental Protection Agency, and the U.S. Centers for Disease Control and Prevention.