A direct result of the COVID-19 pandemic has been a heightened awareness of indoor environmental quality by both building occupants and property owners in the built environment. Direct-reading air quality instruments have long existed to monitor indoor air quality pollutants in real-time. Still, in recent years, advances in sensor technology have resulted in an expansion of air sensors in the indoor air quality market. Air sensors generally refer to a class of technology that provides relatively quick or instant air pollution measurements for a wide variety of air pollutants. The US Environmental Protection Agency (EPA) defines air sensors as “a class of non-regulatory technology that are lower in cost, portable, and generally easier to operate than monitors used for regulatory monitoring purposes.” These non-regulatory types of sensors are sometimes referred to as “low-cost air sensors,” “air sensor devices,” and “air quality sensors.”

The purpose of this article is to provide a summary of how air sensors can be utilized as part of a healthy building program, including discussions regarding the applications and limitations of the current technology.

How can air sensors be used for indoor air quality applications?

Air sensors can be used for a variety of purposes related to indoor air quality (IAQ) and energy optimization in buildings. Due to their low cost and ease of installation, they are increasingly used to provide real-time concentrations of indoor air quality parameters. Air sensors currently on the market can measure a wide variety of general indoor air quality parameters, such as temperature and relative humidity, and airborne pollutants such as carbon monoxide (CO), ozone, particulate matter (PM), volatile organic compounds (VOCs), formaldehyde, chlorine, nitrogen dioxide, hydrogen sulfide, ammonia, nitric oxide, and carbon dioxide (CO2). Air sensors can be set up as a network and are often equipped with cloud-based connectivity for remote monitoring and data uploads. Most sensors are limited to monitoring a maximum of five (5) or six (6) contaminants.

Air sensors have a variety of indoor air quality applications, such as:

• Cost-effective indoor air quality management across a large number of areas/buildings (e.g., real time measurement of CO2, PM, temperature, or relative humidity, to evaluate and adjust HVAC/ventilation settings and identify/prioritize areas for upgrades)
• Awareness and identification of acute problems and pollution hotspots (e.g., measuring CO to identify infiltration from pollutant sources such as idling vehicles or other combustion sources/leaks or VOCs during installation of building finishes)
• Wildfire events (measuring real-time particulate levels to inform wildfire smoke response actions)
• Citizen science projects
• Management of energy and IAQ in buildings (e.g., reducing ventilation rates during times of low/no occupancy by using carbon dioxide as an indicator)*

Can air sensors be used for healthy building certifications?

Yes, air sensors can be used for healthy building certifications, including but not limited to LEED, Fitwel, and WELL. Healthy/green building certification programs (e.g., LEED, Fitwel, WELL) include credits for the monitoring of potential airborne contaminants (as a component of communicating good building health). For example, credits can be earned for monitoring specific indoor air quality contaminants, such as carbon dioxide, carbon monoxide, particulate matter, total volatile organic compounds, ozone, and formaldehyde. The WELL Performance Rating certification provides enhanced credits for the continuous use of air sensors, and the California Collaborative for High Performance Schools (CHPS) criteria version 2.0 includes a requirement for carbon dioxide sensors in each classroom for new school buildings. (You can find more information about these requirements in this recent FACS Insider blog on the topic.)

What are the advantages and limitations of using air sensors?

Advantages of air sensor technology include:

• Relatively low-cost units.
• Small in size and weight, which allows for portability and ease of use.
• Real-time data allows for rapid decision-making.
• Data trend analysis.
• Provide occupants and building owners an understanding of their air quality.
• Often easier to operate than monitors used for regulatory monitoring purposes or traditional environmental monitoring equipment.
• Easy for the non-professional to operate.
• Sensors can be used to assess potential pollutant sources, general ventilation, and building filtration to monitor and help reduce the risk of exposure to particulates, aerosols, and other contaminants to improve the health of building occupants.
• There are a wide variety of sensors available on the emerging commercial market with increased scientific literature evaluating the performance of direct-read sensors.

There are numerous air sensors available for this emerging market with a wide variety of vendors on the market, ranging from established instrument manufacturers to large international industrial hygiene laboratories and HVAC control companies, down to small vendors on the internet. Most of these sensors have smart platforms with applications that provide real-time data and alert systems, with some providing qualitative air quality indices (AQI) with color-coded indicators to assist the end-user in determining if air quality is good, fair, or poor.

Although air sensor technology appears to be the new wave in evaluating air quality and air sensors can be useful for providing information about air quality, individuals using these sensors should have proper training with a general understanding of their limitations and what it means when interpreting the data. Some of the limitations and challenges include the following issues:

• Not all units perform the same. Care should be taken to select the product that best fits the application.
• Air sensors may be inaccurate and, therefore, may require field calibration to give more accurate data.
• While sensors are available to measure a wide variety of contaminants, consideration must be given how the data will be utilized. Just because you can measure something does not mean it provides value and is the best use of resources to ensure healthful indoor environmental quality.
• The generation of defensible data is an issue related to the calibration and validation of data (e.g., accuracy and precision of readings over time). Your plan should include verifying that your sensor is working properly relative to a reference instrument.
• The technology is still under development. Little information exists on the quality of data that sensors produce per manufacturer.
• Most units require an electrical power source and cellular connections that can be affected by power outages and loss of connectivity. This may result in the loss of data.
• There are few regulatory standards for the validation of direct-read sensors.
• Sensor readings can be affected by cross-sensitivities with other contaminants and atmospheric variables, such as temperature and humidity, resulting in false readings.
• There are limited standard procedures for calibration.
• Many air sensors for gasses become less sensitive to the target pollutant over time, resulting in their readings becoming less accurate.
• Most sensors have a relatively short lifetime (1-2 years) and high variability.
• Managing large quantities of data, alarm settings, and communication of data with stakeholders can be an issue. This should be performed under the direction of a competent professional, such as a Certified Industrial Hygienist (CIH).
• Overall cost to set up, maintain, and calibrate the sensors. The total number of sensors required to assess the various functional spaces in a building may become cost prohibitive.
• Many air sensors do not display data on a screen in real time. The user may need to download the data and/or view it on a computer with a specific software or app.

How air sensors should be incorporated into your healthy building program

The use of air sensors can be a viable tool that can be incorporated into a healthy building program if used appropriately. They may be integrated into control measures and serve as a validation mechanism to show control measures are effective. As stated in the US Environmental Protection Agency’s Clean Air in Buildings Challenge, “building owners and operators should engage experts, facilities managers, and others who are skilled, trained, and/or certified in HVAC work to develop and implement plans to improve indoor air quality and manage air flows”.  Validation using traditional industrial hygiene sampling methods should be an integral part of the program that incorporates ANSI/ASHRAE Standards and guidelines from the US EPA, CDC, state, and local agencies. The program should clearly state the role of key players, how the data will be used, how the data will be communicated to stakeholders, and proper training for those responsible for managing the program.

FACS has the experts to assist in the development of your healthy building program to meet you and your building’s specific needs. FACS discourages anyone from purchasing and deploying air sensors without proper planning. There are various steps involved in planning and conducting a useful and successful air monitoring study. Prior to deploying air sensors, you should have a plan clearly stating the purpose of the sampling, how/where sensors will be deployed, and how to process, analyze, and interpret the data. FACS can provide guidance regarding the various types of direct-read sensors, information on available federal funding for building ventilation and IEQ improvements (e.g. American Rescue Plan Act and Bipartisan Infrastructure Law Program for state and local governments, K-12 Schools and higher education), building certifications, data analysis and interpretation, or the development of a site-specific monitoring plan. For additional information on air sensors, visit the US EPA website or give us a call at 888-711-9998.