What to Watch This Week in CO2 Monitoring and Indoor Air Quality

Direct answer: Monitoring indoor air quality (IAQ) requires distinguishing between the removal of particulate matter and the management of gaseous concentrations like carbon dioxide (CO2). Use the checks below to decide what to verify before buying, configuring, or citing the claim.

Who this is for

This is for readers evaluating What to Watch This Week in CO2 Monitoring and Indoor Air Quality who need a practical decision path, clear caveats, and source links before acting.

Related reading path: pair this page with CADR room sizing and CO2 monitor calibration when the decision depends on setup details outside this article.

Quick decision check

Check	Why it matters	What to do next
Measurement target	CO2, CADR, MERV, and airflow measure different things and should not be swapped as if they were one metric.	Identify which pollutant or ventilation question the page is actually answering.
Room and system fit	Room volume, occupancy, noise, filter loading, and HVAC compatibility can change the practical answer.	Apply the guidance to the actual room or system before acting.
Evidence limit	Air cleaners, filters, and sensors can support a plan, but they do not guarantee health outcomes by themselves.	Use the cited source limits before making stronger claims.

Monitoring indoor air quality (IAQ) requires distinguishing between the removal of particulate matter and the management of gaseous concentrations like carbon dioxide (CO2). If the objective is to reduce CO2 levels, increasing outdoor-air ventilation is the primary mechanism; portable HEPA filters and upgraded HVAC filters are designed to capture particles and do not remove CO2 gas from the air [https://www.epa.gov/indoor-air-quality-iaq/air-cleaners-and-air-filters-home]. While CO2 measurements can serve as an indicator of how well a space is being ventilated, these readings do not provide a complete picture of all indoor air quality conditions [https://www.epa.gov/indoor-air-quality-iaq/can-i-measure-carbon-dioxide-co2-indoors-get-information-ventilation].

Technology Baseline: Particulate Filtration vs. Ventilation

Effective indoor air management relies on two distinct technological approaches: filtration and ventilation.

Particulate Filtration

Air cleaners and HVAC filters are tools used to reduce the concentration of pollutants in indoor air [https://www.epa.gov/indoor-air-quality-iaq/air-cleaners-and-air-filters-home]. This includes high-efficiency particulate air (HEPA) filters, which are aimed at capturing particles. The effectiveness of these devices is dependent on two primary factors:

• Capture Efficiency: The ability of the filter media to trap specific particle sizes.
• Airflow: The volume of air passing through the filter.

When evaluating airflow for filtration performance, measurements are typically expressed in cubic feet per minute (CFM) or liters per second (L/s). For example, a device moving 100 CFM is moving approximately 47.2 liters per second (L/s).

The US EPA recommends upgrading HVAC filters to the highest efficiency compatible with the existing system and ensuring a proper fit to prevent bypass [https://www.epa.gov/indoor-air-quality-iaq/air-cleaners-hvac-filters-and-coronavirus-covid-19]. Portable air cleaners should be viewed as supplements to existing ventilation and filtration strategies, particularly in environments where adequate outdoor-air ventilation is difficult to achieve [https://www.epa.gov/indoor-air-quality-iaq/air-cleaners-hvac-filters-and-coronavirus-covid-19].

Ventilation and CO2 Monitoring

Unlike particulate filters, CO2-focused management involves the exchange of indoor air with outdoor air. CO2 is used as a proxy or indicator for ventilation effectiveness [https://www.epa.gov/indoor-air-quality-iaq/can-i-measure-carbon-dioxide-co2-indoors-get-information-ventilation]. High CO2 concentrations often suggest that indoor air is not being adequately replaced by fresh outdoor air, but the presence of CO2 does not directly measure the presence of other pollutants or particles [https://www.epa.gov/indoor-air-quality-iaq/can-i-measure-carbon-dioxide-co2-indoors-get-information-ventilation].

Distinguishing Technology Classes: Consumer Air Cleaning vs. Direct Air Capture

A critical distinction in the field of air management is the difference between consumer-grade air cleaning and Direct Air Capture (DAC).

• Consumer Air Cleaners: These devices (including HEPA filters and HVAC upgrades) are designed to reduce particle concentrations within a localized or building-wide environment [https://www.epa.gov/indoor-air-quality-iaq/air-cleaners-and-air-filters-home]. They are not designed to remove CO2 gas.
• Direct Air Capture (DAC): This is a separate technology class used for removing CO2 from ambient air, primarily for climate and carbon-management purposes [https://www.energy.gov/science/doe-explainsdirect-air-capture]. DAC uses sorbent or solvent-based approaches to capture CO2 from the atmosphere and is distinct from the mechanical filtration of particles found in household air cleaners [https://www.energy.gov/science/doe-explainsdirect-air-capture].

Standards and Frameworks for Aerosol Control

Current guidance for managing infectious aerosols focuses on the concept of "equivalent clean airflow." ASHRAE Standard 241 provides a framework for controlling infectious aerosols by integrating various strategies, including ventilation, filtration, and air-cleaning [https://www.cdc.gov/niosh/ventilation/faq/index.html].

This standard complements broader ventilation mitigation strategies recommended by agencies such as the CDC and NIOSH [https://www.cdc.gov/niosh/ventilation/faq/index.html]. The goal is to achieve a level of air cleaning that is functionally equivalent to a specific rate of clean, outdoor air ventilation.

Comparison Criteria for Air Quality Management

When evaluating monitoring and filtration components, the following fields can be used to structure performance and maintenance data:

Parameter	Component/Metric	Function/Requirement	Maintenance/Update Implications
Pollutant Target	Particulates (PM2.5, etc.)	Reduction of airborne particles via HEPA/HVAC filters	Requires periodic filter replacement and fit checks
Pollutant Target	CO2 Gas	Indicator of ventilation adequacy	Requires monitoring of outdoor-air exchange rates
Airflow Metric	CFM or L/s	Determines the volume of air processed	Effectiveness is dependent on both efficiency and airflow
Standard Compliance	ASHRAE 241	Framework for infectious aerosol control	Focuses on "equivalent clean airflow"
Strategy Type	Supplemental	Portable air cleaners	Used where ventilation is difficult; does not replace ventilation
Technology Class	Direct Air Capture	CO2 removal from ambient air	Distinct from consumer-grade particle filtration

Evidence Gaps and Uncertainties

While CO2 monitoring is a valuable tool, several areas of uncertainty remain in the scientific literature:

• Universal CO2 Thresholds: There is currently no clear scientific consensus on a "one-size-fits-all" CO2 limit for indoor air quality. Research indicates that the evidence base for establishing universal CO2 thresholds is often unclear, and users should avoid treating arbitrary CO2 readings as definitive verdicts on overall air quality [https://www.nature.com/articles/s41370-024-00694-7].
• Comprehensive IAQ Assessment: Because CO2 is only a ventilation indicator, a low CO2 reading does not guarantee the absence of other indoor pollutants, such as volatile organic compounds (VOCs) or fine particulates [https://www.epa.gov/indoor-air-quality-iaq/can-i-measure-carbon-dioxide-co2-indoors-get-information-ventilation].
• Filter Certification: The US EPA does not certify or register specific air cleaners or manufacturers, nor does it provide a list of "acceptable" air cleaners [https://www.epa.gov/indoor-air-quality-iaq/does-epa-certifyregister-or-provide-lists-acceptable-air-cleaners-or]. Users must rely on manufacturer specifications regarding capture efficiency and compatibility with their specific HVAC systems.

What to Watch This Week

For professionals and building managers monitoring indoor environments, the following areas warrant continued observation:

• Ventilation-to-CO2 Correlation: Watch for shifts in CO2 levels as a primary indicator of changes in outdoor-air ventilation rates.
• Implementation of ASHRAE 241: Monitor the adoption of "equivalent clean airflow" strategies, specifically how filtration upgrades and portable air cleaners are being integrated to complement ventilation.
• Filter Compatibility and Fit: Ensure that any upgrades to HVAC filtration (to higher efficiency levels) are accompanied by checks for proper filter fit to prevent air bypass.
• Distinction in Technology Deployment: Maintain a clear distinction between the deployment of particle-reducing air cleaners and the large-scale application of Direct Air Capture technologies for carbon management.

***

Operational Constraints in HVAC and Portable Air Cleaning

When implementing air quality strategies, technical constraints often dictate the limits of effectiveness. For those managing HVAC systems, the primary constraint is the balance between filtration efficiency and system-wide airflow. While upgrading to a higher-efficiency filter can increase the capture of particulates, the US EPA notes that the effectiveness of air cleaners and HVAC filters is fundamentally dependent on both capture efficiency and the volume of airflow [https://www.epa.gov/indoor-air-quality-iaq/air-cleaners-and-air-filters-home].

An upgrade that significantly increases pressure drop without a corresponding increase in fan capacity may reduce the total volume of air processed, potentially undermining the intended air cleaning benefits. Therefore, the recommendation for upgrading filters is specifically to use the highest efficiency level that remains compatible with the existing HVAC system [https://www.epa.gov/indoor-air-quality-iaq/air-cleaners-hvac-filters-and-coronavirus-covid-19].

Furthermore, the deployment of portable air cleaners is constrained by their role as supplemental tools. They are most effectively utilized in scenarios where adequate outdoor-air ventilation is difficult to achieve, rather than as a primary method for managing gaseous pollutants like CO2 [https://www.epa.gov/indoor-air-quality-iaq/air-cleaners-hvac-filters-and-coronavirus-covid-19]. In environments with high-performance ventilation, the marginal utility of portable cleaners may be lower than in "tight" buildings where air exchange is limited.

Specialized Monitoring: CO2 in Acute Care and Hospital Settings

The application of CO2 monitoring extends beyond general office or residential environments into high-stakes clinical settings. In acute care hospitals, CO2 measurements are specifically utilized as a tool to assess the adequacy of ventilation [https://pmc.ncbi.nlm.nih.gov/articles/PMC8627286]. Because the management of infectious aerosols is a critical component of hospital safety, monitoring CO2 concentrations provides a proxy for the effectiveness of air exchange protocols.

Research into hospital environments has explored the use of monitors to actively improve indoor air CO2 concentrations [https://pmc.ncbi.nlm.nih.gov/articles/PMC8556868]. In these settings, the focus is not merely on detecting high levels, but on using the data to drive interventions that ensure ventilation rates are sufficient to mitigate the risks associated with aerosolized pathogens. This aligns with the broader application of ASHRAE Standard 241, which provides a framework for controlling infectious aerosols through integrated ventilation and filtration strategies [https://www.cdc.gov/niosh/ventilation/faq/index.html].

Evaluating Particulate Reduction Efficacy

While CO2 monitoring focuses on ventilation, a complete air quality assessment must also evaluate the efficacy of particulate removal. A key metric in this evaluation is the reduction of PM2.5 (fine particulate matter). The use of HEPA air cleaners has been specifically studied for its efficacy in improving indoor PM2.25 concentrations [https://pmc.ncbi.nlm.nih.gov/articles/PMC9516965].

When auditing air cleaning performance, technical assessments should look for:

• Reduction Percentages: The measurable drop in PM2.5 concentrations following the activation of a HEPA-grade cleaner.
• Clean Air Delivery Rate (CADR): The integration of the filter's capture efficiency with the device's airflow (CFM/L/s) to determine the actual volume of clean air being introduced to the space.

Critical Variables: What Would Change the Assessment?

An environmental audit or a CO2-based ventilation assessment can be rendered inaccurate by several variables. Understanding these "assessment breakers" is vital for maintaining the integrity of indoor air quality data.

• The Presence of Non-Ventilation Pollutants: A low CO2 reading indicates successful outdoor-air exchange, but it does not confirm the absence of other pollutants. If a space has high levels of volatile organic compounds (VOCs) or fine particulates, a low CO2 reading may provide a false sense of security regarding overall air quality [https://www.epa.gov/indoor-air-quality-iaq/can-i-measure-carbon-dioxide-co2-indoors-get-information-ventilation].
• Filter Bypass and Fitment: Even if a high-efficiency filter is installed, if the fit is not precise, air may bypass the filter media. This bypass allows unfiltered air to enter the circulation, meaning the measured reduction in particulates will not reflect the filter's rated efficiency [https://www.epa.gov/indoor-air-quality-iaq/air-cleaners-hvac-filters-and-coronavirus-covid-19].
• Arbitrary Threshold Reliance: Relying on a single, fixed CO2 number as a "pass/fail" metric for air quality is scientifically problematic. Because the evidence base for universal CO2 limits is often unclear, an assessment should be based on trends and correlations with ventilation rates rather than a single arbitrary threshold [https://www.nature.com/articles/s41370-024-00694-7].
• Source Control Neglect: If a pollutant source (such as an indoor combustion process or high-emission activity) is not controlled, even high ventilation rates or efficient filtration may fail to maintain acceptable air quality levels [https://www.epa.gov/indoor-air-quality-iaq/air-cleaners-and-air-filters-home].

Expanded Data Fields for Environmental Audits

To move from simple monitoring to a structured air quality management system, the following data fields should be captured during periodic audits:

Audit Field	Data Type	Purpose
Filter Bypass Check	Boolean (Pass/Fail)	Verifies if air is leaking around the filter frame [https://www.epa.gov/indoor-air-quality-iaq/air-cleaners-hvac-filters-and-coronavirus-covid-19]
PM2.5 Baseline vs. Post-Filter	Numerical ($\mu g/m^3$)	Measures the actual reduction efficacy of HEPA/HVAC units [https://pmc.ncbi.nlm.nih.gov/articles/PMC9516965]
CO2/Ventilation Correlation	Ratio/Trend	Correlates CO2 spikes with occupancy or HVAC activity [https://www.epa.gov/indoor-air-quality-iaq/can-i-measure-carbon-dioxide-co2-indoors-get-information-ventilation]
System Compatibility Status	Text/Status	Confirms if the current filter MERV rating is the highest compatible with the HVAC fan motor [https://www.epa.gov/indoor-air-quality-iaq/air-cleaners-hvac-filters-and-coronavirus-covid-19]
Direct Air Capture (DAC) Proximity	Categorical	Identifies if large-scale CO2 removal technologies are present in the broader ambient environment (for climate-level context) [https://www.energy.gov/science/doe-explainsdirect-air-capture]

Technical Interdependency: The Airflow-Efficiency Trade-off

The technical effectiveness of an air cleaning strategy is governed by the interplay between capture efficiency and the total volume of air processed. When upgrading HVAC filtration, a primary implementation constraint is the increase in static pressure drop associated with higher-efficiency media. While a higher MERV-rated filter provides a greater capacity for capturing fine particulates, it also increases the resistance the HVAC fan must overcome. According to the US EPA, the effectiveness of both portable air cleaners and upgraded HVAC filters is fundamentally dependent on both capture efficiency and airflow [https://www.epa.gov/indoor-air-quality-iaq/air-cleaners-and-air-filters-home].

If the increased resistance of a high-efficiency filter leads to a reduction in the system's airflow (measured in CFM or L/s), the total volume of air being cleaned may decrease, potentially undermining the intended air quality improvements [https://www.epa.gov/indoor-air-quality-iaq/air-cleaners-and-air-filters-home]. Consequently, technical upgrades must be evaluated not just by the filter's ability to trap particles, but by the system's ability to maintain sufficient airflow at the new resistance level [https://www.epa.gov/indoor-air-quality-iaq/air-cleaners-hvac-filters-and-coronavirus-covid-19].

Temporal Analysis: Using CO2 Trends for Ventilation Auditing

Effective CO2 monitoring requires moving beyond snapshot measurements to longitudinal temporal analysis. Because CO2 serves as a proxy for ventilation adequacy, observing concentration trends over time allows for the identification of ventilation decay or failures in air exchange protocols [https://www.epa.gov/indoor-air-quality-iaq/can-i-measure-carbon-dioxide-co2-indoors-get-information-ventilation].

In high-stakes environments, such as acute care hospitals, the use of CO2 monitors is specifically aimed at improving indoor air CO2 concentrations by providing the data necessary to drive ventilation interventions [https://pmc.ncbi.nlm.nih.gov/articles/PMC8556868]. By analyzing the rate of CO2 accumulation during occupancy periods, facility managers can correlate concentration spikes with specific building activities or ventilation system cycles [https://pmc.ncbi.nlm.nih.gov/articles/PMC8627286]. This approach enables the identification of periods where the outdoor-air exchange rate is insufficient to mitigate the risks of aerosolized pathogens, supporting the broader objectives of ASHRAE Standard 241 for infectious aerosol control [https://www.cdc.gov/niosh/ventilation/faq/index.html].

The Mitigation Hierarchy: Integrating Source Control, Ventilation, and Filtration

A comprehensive indoor air quality management strategy is structured around a hierarchy of three distinct control layers: source control, ventilation, and filtration.

• Source Control: This is the foundational layer, focusing on the reduction or elimination of pollutants at their point of origin [https://www.epa.gov/indoor-air-quality-iaq/air-cleaners-and-air-filters-home].
• Ventilation: This layer focuses on the dilution of indoor pollutants through the introduction of outdoor air. CO2 monitoring is a primary tool for assessing the

adequacy of outdoor-air exchange. This hierarchy ensures that the most effective and permanent solutions—removing the pollutant at the source—are prioritized before relying on secondary methods like dilution (ventilation) or capture (filtration) [https://www.epa.gov/indoor-air-quality-iaq/air-cleaners-and-air-filters-home].

Technical Implementation: The Airflow-Efficiency Constraint

When upgrading HVAC systems, the primary technical hurdle is the relationship between filter resistance and fan performance. The US EPA recommends upgrading to the highest efficiency level that is compatible with the existing HVAC system [https://www.epa.gov/indoor-air-quality-iaq/air-cleaners-hvac-filters-and-coronavirus-covid-19]. This compatibility is not merely about the physical dimensions of the filter, but about the impact of the filter's pressure drop on the system's ability to move air.

Because the effectiveness of both portable air cleaners and upgraded HVAC filters is fundamentally dependent on both capture efficiency and the volume of airflow, an upgrade that increases particle capture but significantly reduces the total volume of air processed may result in a net loss of air cleaning performance [https://www.epa.gov/indoor-air-quality-iaq/air-cleaners-and-air-filters-home]. Therefore, a successful implementation requires verifying that the airflow (measured in CFM or L/s) remains sufficient to meet the building's ventilation and filtration requirements after the higher-efficiency media is installed [https://www.epa.gov/indoor-air-quality-iaq/air-cleaners-and-air-filters-home].

Comparative Framework for Air Management Strategies

To effectively manage indoor environments, technical operators must distinguish between the operational roles of three primary technology classes:

• HVAC Filtration Upgrades (Primary Particulate Control):

* Mechanism: Increasing the MERV rating of existing filters to capture finer particulates. * Constraint: Limited by the highest efficiency level compatible with the existing HVAC fan motor and airflow requirements [https://www.epa.gov/indoor-air-quality-iaq/air-cleaners-hvac-filters-and-coronavirus-covid-19]. * Metric: Capture efficiency and airflow (CFM/L/s) [https://www.epa.gov/indoor-air-quality-iaq/air-cleaners-and-air-filters-home].

• Portable Air Cleaners (Supplemental Particulate Control):

* Mechanism: Localized HEPA-grade filtration to reduce particle concentrations. * Constraint: These are supplemental tools and should not be used as replacements for ventilation, particularly in areas where outdoor-air exchange is difficult [https://www.epa.gov/indoor-air-quality-iaq/air-cleaners-hvac-filters-and-coronavirus-covid-19]. * Metric: Clean Air Delivery Rate (CADR) and PM2.5 reduction efficacy [https://pmc.ncbi.nlm.nih.gov/articles/PMC9516965].

• Ventilation (Gaseous and Aerosol Dilution):

* Mechanism: Increasing the exchange of indoor air with outdoor air to dilute pollutants. * Constraint: Effectiveness is monitored via CO2 as a proxy, but does not directly measure all pollutants [https://www.epa.gov/indoor-air-quality-iaq/can-i-measure-carbon-dioxide-co2-indoors-get-information-ventilation]. * Metric: CO2 concentration trends and outdoor-air exchange rates [https://www.epa.gov/indoor-air-quality-iaq/can-i-measure-carbon-dioxide-co2-indoors-get-information-ventilation].

Advanced Monitoring Protocols in Clinical Environments

In high-stakes clinical settings, such as acute care hospitals, monitoring protocols must transition from general occupancy indicators to active ventilation management. In these environments, CO2 measurements are specifically utilized as a tool to assess the adequacy of ventilation [https://pmc.ncbi.nlm.nih.gov/articles/PMC8627286].

The objective in these settings is to use real-time data to drive interventions that ensure ventilation rates are sufficient to mitigate the risks associated with aerosolized pathogens [https://pmc.ncbi.nlm.nih.gov/articles/PMC8556868]. This specialized application of CO2 monitoring aligns with the principles of ASHRAE Standard 241, which provides a framework for controlling infectious aerosols through integrated strategies that combine ventilation and filtration [https://www.cdc.gov/niosh/ventilation/faq/index.html].

The Limits of Single-Metric Monitoring

A critical limitation in current IAQ monitoring is the reliance on single-pollutant proxies. While CO2 is a useful indicator for ventilation, it is not a comprehensive metric for air quality.

• The Proxy Gap: A low CO2 reading indicates successful outdoor-air exchange but does not confirm the absence of other indoor pollutants, such as volatile organic compounds (VOCs) or fine particulates [https://www.epa.gov/indoor-air-quality-iaq/can-i-measure-carbon-dioxide-co2-indoors-get-information-ventilation].
• The Threshold Uncertainty: Because the scientific evidence base for establishing universal CO2 limits is often unclear, monitoring programs should avoid treating arbitrary CO2 thresholds as definitive verdicts on overall air quality [https://www.nature.com/articles/s41370-024-00694-7].
• The Certification Gap: When evaluating new equipment, users must recognize that the US EPA does not certify or provide lists of "acceptable" air cleaners or manufacturers [https://www.epa.gov/indoor-air-quality-iaq/does-epa-certifyregister-or-provide-lists-acceptable-air-cleaners-or]. All performance claims regarding capture efficiency must be verified against manufacturer specifications and system compatibility.

Decision Logic for Environmental Audits

To standardize air quality assessments, facility managers can utilize the following decision logic based on observed environmental data:

If Observed Condition Is...	Then Technical Action Required Is...	Primary Constraint/Consideration
Rising CO2 Trends	Evaluate and increase outdoor-air exchange/ventilation rates [https://www.epa.gov/indoor-air-quality-iaq/can-i-measure-carbon-dioxide-co2-indoors-get-information-ventilation]	Ventilation is the primary mechanism for CO2 management.
High PM2.5 Concentrations	Verify HEPA/HVAC filter efficiency and check for air bypass [https://pmc.ncbi.nlm.nih.gov/articles/PMC9516965, https://www.epa.gov/indoor-air-quality-iaq/air-cleaners-hvac-filters-and-coronavirus-covid-19]	Effectiveness depends on both capture efficiency and airflow [https://www.epa.gov/indoor-air-quality-iaq/air-cleaners-and-air-filters-home].
Upgrading HVAC Filters	Verify the new filter is the highest efficiency compatible with the existing system [https://www.epa.gov/indoor-air-quality-iaq/air-cleaners-hvac-filters-and-coronavirus-covid-19]	Increased resistance may reduce total airflow (CFM/L/s) [https://www.epa.gov/indoor-air-quality-iaq/air-cleaners-and-air-filters-home].
Limited Ventilation Access	Deploy portable air cleaners as a supplemental strategy [https://www.epa.gov/indoor-air-quality-iaq/air-cleaners-hvac-filters-and-coronavirus-covid-19]	Portable cleaners do not replace the need for ventilation.

FAQ

What should I measure first?

Measure the variable the article is about, then separate particle cleaning, ventilation, CO2 indication, and source control before deciding what to change. For this page, apply that answer to What to Watch This Week in CO2 Monitoring and Indoor Air Quality.

Does one number prove the room is safe?

No. A single CO2, CADR, or filter rating needs room context, maintenance context, and source-specific limits. For this page, apply that answer to What to Watch This Week in CO2 Monitoring and Indoor Air Quality.

What should I do after reading?

Use the checklist or table to choose the next practical step, then verify it against the cited public guidance. For this page, apply that answer to What to Watch This Week in CO2 Monitoring and Indoor Air Quality.

Sources

• US EPA: https://www.epa.gov/indoor-air-quality-iaq/air-cleaners-and-air-filters-home
• US EPA: https://www.epa.gov/indoor-air-quality-iaq/air-cleaners-hvac-filters-and-coronavirus-covid-19
• CDC/NIOSH: https://www.cdc.gov/niosh/ventilation/faq/index.html
• US Department of Energy: https://www.energy.gov/science/doe-explainsdirect-air-capture
• US EPA: https://www.epa.gov/indoor-air-quality-iaq/can-i-measure-carbon-dioxide-co2-indoors-get-information-ventilation
• Journal of Exposure Science & Environmental Epidemiology: https://www.nature.com/articles/s41370-024-00694-7
• US EPA: https://www.epa.gov/indoor-air-quality-iaq/does-epa-certifyregister-or-provide-lists-acceptable-air-cleaners-or