Response to comments on “The influence of mechanical ventilation and portable air cleaners upon aerosol spread in a hospital outpatients clinic” by Salmonsmith et al.

Comments on “The influence of mechanical ventilation and portable air cleaners upon aerosol spread in a hospital outpatients clinic” by Salmonsmith et al.

The influence of mechanical ventilation and portable air cleaners upon aerosol spread in a hospital outpatients clinic

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

Usage and impact of a do-it-yourself air cleaner on residential PM2.5 in a smoke-impacted community

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

A novel method for determining whole house particle removal and clean air delivery rates attributable to central and portable ventilation/air cleaning systems is described. The method is used to characterize total and air-cleaner-specific particle removal rates during operation of four in-duct air cleaners and two portable air-cleaning devices in a fully instrumented test home. Operation of in-duct and portable air cleaners typically increased particle removal rates over the baseline rates determined in the absence of operating a central fan or an indoor air cleaner. Removal rates of 0.3- to 0.5-μm particles ranged from 1.5 hr−1 during operation of an in-duct, 5-in. pleated media filter to 7.2 hr−1 for an in-duct electrostatic air cleaner in comparison to a baseline rate of 0 hr−1 when the air handler was operating without a filter. Removal rates for total particulate matter less than 2.5 μm in aerodynamic diameter (PM2.5) mass concentrations were 0.5 hr−1 under baseline conditions, 0.5 hr−1 during operation of three portable ionic air cleaners, 1 hr−1 for an in-duct 1-in. media filter, 2.4 hr−1 for a single high-efficiency particle arrestance (HEPA) portable air cleaner, 4.6 hr−1 for an in-duct 5-in. media filter, 4.7 hr−1 during operation of five portable HEPA filters, 6.1 hr−1 for a conventional in-duct electronic air cleaner, and 7.5 hr−1 for a high efficiency in-duct electrostatic air cleaner. Corresponding whole house clean air delivery rates for PM2.5 attributable to the air cleaner independent of losses within the central ventilation system ranged from 2 m3/min for the conventional media filter to 32 m3/min for the high efficiency in-duct electrostatic device. Except for the portable ionic air cleaner, the devices considered here increased particle removal indoors over baseline deposition rates.

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 ≥8 hours/day; commercial PAC usage ≥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 (≥30% of phase) of either PAC was significantly associated with improved health (measured as a composite score), relative to low usage (<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

Field measurement of the impact of natural ventilation and portable air cleaners on indoor air quality in three occupant states

Can portable air cleaners reconcile conflicting needs for open-door/window autonomy and indoor air quality for occupants in densely populated offices?

P-317 Introduction: In this paper, we report the efficacy of a variety of in-duct and portable air cleaners for control of PM exposure indoors based on trials conducted under controlled conditions in a fully characterized test home. Methods: Aerosol challenge trials were test conducted inside a 120 m2 test home equipped with a typical forced air ventilation system. In-duct air cleaners included a conventional filter (F1), a pleated fabric filter (F5), a conventional electronic air cleaner (EAC), and a new electrostatics technology (ifD) that relies upon an annular field charger and collection flutes coated with a dielectric material. Portable air cleaners (PAC) included a 6.2 m3/min (220 cfm) unit with a HEPA filter and an ionic unit that operates without a fan (IB). Continuous size-resolved particle number concentrations from multiple rooms in the test home were used to ascertain particle decay rates, whole house particle concentrations, and steady-state particle concentrations following emission of a standard polydisperse fine test dust. Results: Particle decay rates and concentrations in the test home varied substantially among the in-duct and portable air cleaners evaluated. Decay rates for 0.3 to 0.5 μ m particles ranged from less than 0.1 per hour (h-1) when neither the air handling unit (AHU) nor an air cleaner (AC) were operated to 7.2 h-1 during operation of the ifD. Performance of five PAC (3.9 h-1) approached the EAC (4.6 h-1), while tests with one PAC and three IB both resulted in removal rates of approximately 1.4 and 0 h-1, respectively. Similar results were obtained for larger particle sizes including those that contribute most to PM2.5 mass concentrations, except that removal rates were greater overall because of particle deposition to surfaces within the home (Table 1).Table 1: Whole House Removal Rates for 1- 3 μm Particles Measured in a Central Room of the Test HomeSteady-state concentrations achieved by the various systems tested were inversely related to decay rate. For example, steady-state indoor levels for the ifD were 2% of outdoor concentrations, 4% for the EAC, 19% for the 1″ filter, 10% for 1 PAC, and 28% for three IB. Discussion and Conclusions: These experiments carried out under simulated real-world conditions indicate that particle removal rates and whole house particle number concentrations indoors can vary by a factor of 10 or more depending upon the use of in-duct and portable air cleaning systems in a home. These results indicate that the greatest reduction in exposure is achieved by high efficiency, high airflow in-duct air cleaning systems. Use of indoor air cleaners could be an important modifier of PM-health relationships observed in epidemiological studies.

Self-reported health impacts of do-it-yourself air cleaner use in a smoke-impacted community

Background: Fine particulate matter air pollution (PM2.5) exposure is linked with increased risk of cardiovascular disease (CVD) events, increases in blood pressure and inflammation. By decreasing PM2.5 concentrations, portable air cleaners (PACs) reduce PM2.5 exposure and may mitigate inflammatory responses to exposure. We hypothesized that PAC use is associated with changes in serum concentrations of protein biomarkers associated with CVD risk. Aim: We aimed to quantify changes in protein biomarkers after 4 weeks of PAC use to provide insights into the proteomic response to reduced PM2.5. Methods: We performed a randomized, double-blind, sham-controlled trial of PACs in 44 outpatient adults with stable HTN and no known CVD. Participants were randomly assigned to either the true PAC group or the sham PAC (placebo) group. Serum concentrations of 369 protein biomarkers associated with CVD risk were measured using the Olink Cardiometabolic Explore I panel before and after 4 weeks of PAC use. The associations between PAC use and changes in protein concentrations were analyzed using linear mixed-effects models, adjusting for age, sex and BMI. Results: Median (IQR) age of participants was 57.5 (51-68) years, 29 (66%) were female, and 21 (48%) had BMI > 30. The changes in expression of 7 protein biomarkers after air filtration differed significantly comparing true versus sham: SSC5D, F7, GH1, LEPR, TFPI, COL4A1, THPO (all p-values < 0.05 for interaction term). SSC5D and THPO were downregulated while the remainder were upregulated. PAC use may have beneficial effects on pathways associated with blood coagulation (increased F7 and TFPI, decreased THPO) and healing (increased LEPR, COL4A1, GH1) and innate immune response (decreased SSC5D). Though most of these have not been directly studied in relation to PM2.5, F7 has been shown to decrease with increased air pollution, concordant with our results. Conclusions: We showed significant effects of air filtration on serum concentrations of seven protein biomarkers linked with CVD. These results provide insight into potential mechanisms by which PAC use may reduce CVD risk.

Portable air cleaners (PACs) equipped with high-efficiency particulate air (HEPA) filters are recommended to reduce indoor particulate matter (PM) exposure from wildfire smoke, particularly in regions like the Pacific Northwest, where seasonal wildfires affect air quality. While many studies have evaluated the long-term effectiveness of HEPA PACs, few have focused on the effects of dust loading and their performance in filtering woodsmoke over extended periods. This study investigated the impact of filter dust loading on the performance of a HEPA PAC (Winix C535, Winix America) in reducing woodsmoke particles. Filters were pre-loaded with varying amounts of ASHRAE ISO 12103–1 A2 fine test dust, and an exposure chamber was used to assess clean air delivery rate (CADR), airflow rate, and power consumption. Results indicated a significant decline in PAC performance with increasing filter loading, highlighting the importance of regular filter replacements to maintain effective operation. Based on simulations considering dynamic indoor PM2.5 concentration, in a typical scenario with a 90-m² room, baseline PM2.5 emission rates, and continuous operation at fan speed Level 2 (5-year mean indoor PM2.5: 2.99 μg/m3), it would take over 5 years for the PAC filters to accumulate 46 g of dust – an amount associated with a significant drop in CADR observed in the study. These findings suggest that the commonly recommended 1-year replacement schedule by manufacturers may be overly conservative for such conditions. By utilizing indoor air quality sensors to monitor PM concentrations, users can tailor filter replacement schedules to maintain optimal PAC performance in real-world environments.

Secondary VOCs emission from used fibrous filters in portable air cleaners and ventilation systems

The utilization of portable air cleaners (PACs) is a recommended supplemental approach to help remove airborne pathogens and mitigate disease transmission in learning environments. To improve PAC effectiveness, science-based information is needed to optimize their implementation strategies such as the deployment location, height, and number of PACs. In this study, we developed a Computational Fluid Dynamics (CFD) model to assess how PACs perform in occupied classrooms equipped with displacement and mixing ventilation systems. The results show that PACs with a flow rate of 2.6 h-1 reduce the mean aerosol intake of all students by up to 66%. A key benefit of using PACs is to facilitate air mixing and movement in indoor environments with inadequate ventilation, thereby effectively reducing high aerosol concentrations near the infector. Furthermore, our results highlight the impact of PAC location on its performance. PACs achieve the best effectiveness when placed closed to the infector (within a distance <3 m). In the absence of knowing who is infected, deploying a PAC at the center of the room is recommended. Moreover, adjusting PAC flow discharge height to the breathing height of occupants (e.g., 0.9-1.2 m for seated people) can enhance their effectiveness in spaces with poor air mixing.