Key Definitions
Air Pollution
Air pollution is the combination of tiny airborne particles (solid or liquid) and certain gases that are mixed into the air around us, making it less healthy to breathe. These air pollutants mostly come from human activities such as car and lorry exhausts, factory smoke, and even from the furniture in our buildings and paint on our walls. However, some of the particles, such as desert dust (which can travel from the Sahara!) and mould spores, come from natural sources.
We can measure the 'particulate matter' (PM) (or particles) in the air. Some of the gases found in our air are produced by commonly used solids and liquids naturally evaporating, these gases are typically volatile organic compounds (or VOCs - almost everything you smell is a VOC!). Other gases that are common air pollutants include nitrogen dioxide, sulphur dioxide, ozone or carbon monoxide.
The SAMHE monitors measure particulate matter, total volatile organic compounds but also carbon dioxide, along with temperature and relative humidity. We're measuring carbon dioxide (CO2) because, although it is not actually a pollutant, it is a reliable indicator of some aspects of indoor air quality; higher indoor concentrations of CO2 indoors correspond with high levels of rebreathed air and a lack of fresh air supplied to the room. For more information on what air pollution is, visit the Clean Air Hub.
Air quality
Air quality describes how polluted the air we breathe is. It is important because the presence of air pollution can have a direct impact on our health, both in the long and short term.
Carbon dioxide
Carbon dioxide (CO2) is a gas found in the air around us. The most common source of CO2 indoors in schools is people who breathe it out. If a room is well ventilated, CO2 levels are usually much lower. Because of this, CO2 is a good indication of the ventilation each person might be experiencing: with higher CO2 levels showing an increase in stale air and a lack of fresh air supplied to the room.
Outside, the typical concentration of CO2 is around 415 ppm (parts per million) although it can be higher in cities. For more information about background CO2 levels and how they have changed over time, see NASA's climate pages.
A well-ventilated classroom should have CO2 concentrations below 800 ppm (shown by the green LEDs on your SAMHE monitor and explained in our monitor guidance). If the reading is between 800 and 1,500 ppm (orange LEDs), the room is potentially stuffy and steps could be taken to improve the ventilation to the room (for example, by opening windows).
Consistent readings above 1,500 ppm (red LEDs on your SAMHE monitor) could indicate that the classroom ventilation needs improving, if the levels keep rising above 1,500 ppm then please seek support from your Senior Leadership Team. Even at this level, CO2 is not itself dangerous to our health, it is very different to poisonous gases, such as carbon monoxide. However, lower CO2 levels have been shown to help with our concentration and improving the ventilation could also help with the student's learning.
For more information on the LEDs see our guide to monitor LEDs during normal operation available on the Resources Page. General information on CO2 and the use of monitors to manage ventilation can be found on the CoSchools website.
Particulate Matter
Particulate matter is small bits of matter that we can breathe in. The monitors measure the fine particles, PM2.5, which include most of the particles smaller than 2.5 microns and are invisible to the naked eye. They can come from different sources, some of which are outdoors, for example traffic, whilst others come from indoors, for example, cooking or dust from carpets.
Total volatile organic compounds
The monitors also detect total volatile organic compounds (TVOCs). Volatile organic compounds, or VOCs, are chemicals that evaporate into the air from liquids or solids commonly found indoors. VOCs come from a range of sources like cleaning products, air fresheners, paint or cooking.
Relative humidity
Relative humidity is a measure of the moisture in the air around us. It is useful to measure because it tells us how comfortable people might be in the room.
Temperature
The monitors also measure temperature. This is another useful factor to measure, because it can show how comfortable the room might feel to students and staff, and whether the heating systems, and the ventilation, are working well. If the ventilation is really good (with a CO2 reading well below 800 ppm) and the room is too cold, then you could consider having your windows slightly less wide open. Keep referring back to your SAMHE monitor as you make adjustments.