The Role of Portable Air Purifiers and Effective Ventilation in Improving Indoor Air Quality in University Classrooms

In this study we investigated the effectiveness of air purifiers and in-line filters in ventilation systems working simultaneously inside various classrooms at the University of Southern California (USC) main campus. We conducted real-time measurements of particle mass (PM), particle number (PN), and carbon dioxide (CO₂) concentrations in nine classrooms from September 2021 to January 2022. The measurement campaign was carried out with different configurations of the purifier (i.e., different flow rates) while the ventilation system was continuously working. Our results showed that the ventilation systems in the classrooms were adequate in providing sufficient outdoor air to dilute indoor CO₂ concentrations due to the high air exchange rates (2.63-8.63 h^-1). The particle penetration coefficients (P) of the investigated classrooms were very low for PM (<0.2) and PN (<0.1), with the exception of one classroom, corroborating the effectiveness of in-line filters in the ventilation systems. Additionally, the results showed that the efficiency of the air purifier exceeded 95% in capturing ultrafine and coarse particles and ranged between 82-88% for particles in the accumulation range (0.3-2 µm). The findings of this study underline the effectiveness of air purifiers and ventilation systems equipped with efficient in-line filters in substantially reducing indoor air pollution.

Portable HEPA Purifiers to Eliminate Airborne SARS-CoV-2: A Systematic Review

OBJECTIVE

Current epidemiologic predictions of COVID-19 suggest that SARS-CoV-2 mitigation strategies must be implemented long-term. In-office aerosol-generating procedures pose a risk to staff and patients while necessitating examination room shutdown to allow aerosol decontamination by indwelling ventilation. This review summarizes the current state of knowledge on portable high-efficiency particulate air (HEPA) purifiers' effectiveness in eliminating airborne SARS-CoV-2 from indoor environments.

DATA SOURCES

Medline, Embase, Cochrane Databases, and the World Health Organization's COVID-19 Global Literature on Coronavirus Disease.

REVIEW METHODS

Data sources were systematically searched for original English-language published studies indexed up to January 14, 2021 per the following search strategy: ("HEPA" OR "High-efficiency" OR "High-efficiency particulate air" OR "Efficiency particulate" OR "Purifier" OR "Filter" OR "Cleaner" OR "Filtration") AND ("COVID" OR "COVID-19" OR "SARS-CoV-2" OR "Coronavirus"). Additional relevant studies were identified by searching the reference lists of included articles.

RESULTS

Eleven published studies have evaluated the effectiveness of portable HEPA purifiers in eliminating airborne SARS-CoV-2 with relevantly sized surrogate particles. Ten studies evaluated aerosols and submicron particles similar in size to SARS-CoV-2 virions. In all studies, portable HEPA purifiers were able to significantly reduce airborne SARS-CoV-2-surrogate particles. The addition of portable HEPA purifiers augmented other decontamination strategies such as ventilation.

CONCLUSION

Experimental studies provide evidence for portable HEPA purifiers' potential to eliminate airborne SARS-CoV-2 and augment primary decontamination strategies such as ventilation. Based on filtration rates, additional air exchanges provided by portable HEPA purifiers may be calculated and room shutdown times potentially reduced after aerosol-generating procedures.

Creating Clean Air Spaces During Wildland Fire Smoke Episodes: Web Summit Summary

Effective strategies to reduce indoor air pollutant concentrations during wildfire smoke events are critically needed. Worldwide, communities in areas prone to wildfires may suffer from annual smoke exposure events lasting from days to weeks. In addition, there are many areas of the world where high pollution events are common and where methods employed to reduce exposure to pollution may have relevance to wildfire smoke pollution episodes and vice versa. This article summarizes a recent virtual meeting held by the United States Environmental Protection Agency (EPA) to share research, experiences, and other information that can inform best practices for creating clean air spaces during wildland fire smoke events. The meeting included presentations on the public health impacts of wildland fire smoke; public health agencies' experiences and resilience efforts; and methods to improve indoor air quality, including the effectiveness of air filtration methods [e.g., building heating ventilation and air conditioning (HVAC) systems and portable, free-standing air filtration systems]. These presentations and related research indicate that filtration has been demonstrated to effectively improve indoor air quality during high ambient air pollution events; however, several research questions remain regarding the longevity and maintenance of filtration equipment during and after smoke events, effects on the pollution mixture, and degree to which adverse health effects are reduced.