Carbon dioxide (CO2) is a colorless, odorless gas. It’s also the primary greenhouse gas contributing to climate change and a common air pollutant both indoors and out.

Monitoring carbon dioxide – a positive step towards ensuring cleaner air for teachers, faculty, and children – is just one component in a wide range of school-focused air, energy, and water environmental considerations.

School districts are required to upgrade their building ventilation and HVAC systems as well as replace filters to reduce indoor pollutant and airborne infection exposure in classrooms.

The following is a look at CO2 monitoring and schools, including:

• what are safe and unsafe varying concentrations of indoor CO2
• what particulate pollutants are and why they pose a greater danger than other pollutants
• why a more comprehensive indoor and outdoor approach to air quality monitoring is important for healthy schools
• how air pollution monitoring can help you achieve compliance with state and federal school guidelines

What are safe levels of CO2?

Outdoor and indoor CO2 can have different primary sources. While outdoor CO2 is generated primarily from industry and vehicle exhaust, indoor CO2 is more frequently associated with human exhalation and fuel use.

When outdoor concentrations of CO2 are high, it can enter buildings and worsen air quality. However, tightly sealing buildings against outdoor air can lead to an even greater indoor buildup of CO2. When windows are closed to retain heat on cold days, reduced ventilation can also build up CO2.

CO2 concentrations are measured in parts per million (ppm). Concentrations of 250-350 ppm are commonly found outdoors. CO2 concentrations in the range of 350-1,000 ppm are considered typical in occupied spaces with decent ventilation. CO2 concentrations in the range of 1,000 to 5,000 ppm are considered unhealthy and concentrations over 5,000 ppm could be dangerous.

Classroom CO2 monitors should provide an alert when carbon dioxide levels rise above 1,100 ppm. A typical air quality monitor equipped with accurate CO2 sensors will detect this range of carbon dioxide.

Providing an alert at 1,100 ppm is important but might not prevent CO2 from rising high beyond that. Because indoor CO2 levels can be harmful to human health, it is important to set the alert threshold below this level – possibly to 900 or 1,000 ppm.

Concentrations between 1,000 and 2,000 ppm

When CO2 concentrations are over 1,000 ppm, this can lead to feelings of drowsiness, stuffiness, and mild confusion(1,2).

Concentrations between 2,000 and 5,000 ppm

At concentrations between 2,000 to 5,000 ppm, there can be an increase in symptoms associated with elevated CO2 exposure, including:

• poor concentration and attention
• increased heart rate
• mild nausea

Concentrations over 5,000 ppm

CO2 concentrations over 5,000 ppm are dangerous and could lead to toxicity and oxygen deprivation.

Why particulate pollutants matter

While simply installing CO2 monitors can help protect students and faculty from CO2 buildup in the classroom, it shouldn’t be administrators’ only air quality consideration. Indoor CO2 monitoring alone won’t do enough to alert schools to the most dangerous and pervasive air pollutants, and it won’t notify teachers and faculty about high levels of outdoor air pollutants.

CO2 is an important pollutant to measure and control. However, particle pollutants are more prevalent and dangerous. Both CO2 and particle pollutants are important to control and, if left unaddressed, are dangerous in the classroom.

One of the major sources of particle pollutants is wildfires. Climate change has intensified and lengthened historic wildfires. In late 2020 alone, wildfires brought unhealthy air into the lungs of 38 million people in Washington State, Oregon, Idaho, Montana, and California for at least five days (3).

When schools are located near major roadways and industry, students and faculty may be regularly exposed to particulate pollutants. According to a 2014 study published in the Journal of Exposure Science & Environmental Epidemiology, 6.4 million U.S. children were attending schools within 250 meters of a major roadway (4)

Proximity to particle pollutants from roadways can harm academic performance. According to data from the National Bureau of Economic Research, students who moved from an elementary or middle school into a middle school or high school in the same zip code that was downwind from traffic pollution experienced lower test scores, more absences, and more reported behavioral issues(5).

Wildfires, industrial pollution, and vehicle exhaust can increase airborne pollutants, including:

• carbon dioxide
• ozone
• carbon monoxide
• volatile organic compounds (VOCs)
• nitrogen dioxide

The primary pollutant emitted by these sources is particulate matter pollution (6)

Particulate matter pollutants include:

PM10: Composed of larger particles and commonly known as dust, PM10 is large and more easily filtered from the airways than smaller particles. PM10 can cause short-term and long-term cardiovascular and respiratory damage.

PM2.5: Due to its tiny size, PM2.5 can stay suspended in the air much longer than larger particles and can be absorbed into the bloodstream when inhaled. Because PM2.5 can enter the circulatory system, PM2.5 carries a wide range of severe health threats to the body, and was associated with 160,000 deaths in the world’s top five most populous cities during 2020.

PM1: PM1is much like PM2.5, except that it’s smaller in diameter, has a larger surface area, and is more likely to enter the bloodstream than PM2.5. Because of the larger surface area of PM1, it is more likely to carry toxic chemicals on its surface (7). Like PM2.5, PM1 is mostly commonly caused by combustion, which can impact schools near major roadways.

Air quality monitors are designed to measure a range of pollutants in the air. Among the deadliest detected pollutants are PM2.5, fine particles.

Monitoring CO2 and PM2.5 can help protect a classroom from air pollution. However, this requires a comprehensive approach to pollutant detection monitoring be combined with ventilation and air filtration truly manage indoor air pollution.

Comprehensive pollutant detection

While a typical carbon dioxide monitor installed in classrooms should alert teachers and faculty to high concentrations of CO2 buildup, this isn’t enough to help keep the air safe. Without monitors for detecting even more dangerous particulate matter pollution, a CO2 detection device is only part of the air quality solution.

AirVisual Series air quality monitors provide more comprehensive air quality data tools to leverage both indoor and outdoor air quality measurements for automated control of filtration and ventilation that can help reduce indoor CO2 and other air pollutants, such as particulate matter and airborne infections.

Sensors used in the AirVisual Series detect and display both PM2.5 and CO2 pollutants as well as temperature and humidity in each classroom. This data can be used to alert teachers about rising air pollution measurements through the AirVisual Pro visual interface as well as through the AirVisual app. This data can also be coupled with building management systems using APIs or IFTTT triggers to automatically turn on HVAC fans for ventilation and filtration when PM2.5 or CO2 reach critical thresholds.

Outdoor air quality also strongly impacts indoor air quality. Although opening windows and doors can help reduce indoor build-up of CO2, this can also worsen indoor air quality when there are high levels of pollutants outdoors. That’s why it’s crucial to know the air quality in both environments, in particular for schools that are near major roadways or industrial facilities.

The AirVisual Outdoor air quality monitor can provide onsite air quality data, empowering schools with a full picture of outdoor air pollutants. The AirVisual Outdoor can measure particulate matter ranging from 0.3 microns to 10 microns in size, a full spectrum of particulate pollutants, with modular field-swappable sensors including the optional CO2 sensor. Weatherized encasement makes it ideal for use in almost any outdoor environment.

AirVisual Series air quality monitors can be used as part of a building automation system to trigger ventilation and filtration in direct response to rising pollution levels. Using custom IFTTT applets and APIs, air quality monitors can be integrated into HVAC or HEPA air filtration system management tools, with air quality data readings triggering HVAC actions that help improve indoor air quality.

For example, if an AirVisual monitor records CO2 levels at 900 to 1,000 ppm, building administrators can set up an IFTTT applet to use this data along with an Internet of Things (IoT)-compatible smart plug to activate HVAC system fans and ventilate the space until CO2 levels fall under that threshold again.

In this way, automation triggered by real-time air quality monitoring promotes energy efficiency, lower building costs, and greater school safety. By automating HVAC ventilation and filtration only when pollutants reach certain levels, this can help reduce the need to operate HVAC systems around the clock.

Automation tools can also help leverage your air quality data to efficiently ventilate CO2 and filter pollutants, such as particulate matter down to 0.003 microns, with high-efficiency air filtration systems that operate when certain thresholds are reached.

MERV 13 is commonly recommended to help mitigate transmission of infectious aerosols, but has many shortcomings related to energy efficiency and filtration capabilities. MERV 16 and above, such as with NanoMax filtration, helps ventilate CO2 while also filtering up to 90% of particles down to 0.003 microns without requiring ventilation beyond what's required by building codes.

To better help ensure that classrooms improve classroom air quality, schools can join the Clean Air Schools program. A tailored clean air solution comes with an on-site assessment, installation, maintenance, air quality verification, monitoring, and renewal all built-in to the program.

By automating and integrating monitoring, ventilation, and filtration systems, schools can best meet state and federal clean air requirements and help keep classroom air clean.

The takeaway

When it comes to children’s safety, it’s not enough to simply try to meet the letter of the law. While it’s important to monitor CO2 levels, it’s also vital to the health of students, teachers, and faculty to provide a more comprehensive pollutant monitoring solution.

The ideal air quality monitoring solution keeps track of particulate matter, CO2, temperature, and humidity, while providing a platform for the use of air quality data to automate air ventilation filtration solutions for school building safety.