Why schools need clean air indoors

The school environment has a critical impact on the health and wellbeing of children. Providing well-ventilated classrooms to reduce the risk of catching COVID-19 has been recommended by ventilation and air quality scientists since the start of the pandemic, but the provision of clean air to keep children safe is not just a COVID-19 issue. 

It has been well known for decades that poor air quality in school classrooms has been impacting children’s learning. There’s a large body of research that shows that poor ventilation and pollution, which is highly prevalent around urban schools, has major effects on children’s health, performance and wellbeing. School staff are also affected by poor air quality and they have a right to a safe working environment.

The Lancet COVID-19 Commission Task Force on Safe Work, Safe School, and Safe Travel found that most schools in the US do not meet even the minimum ASHRAE (American Society of Heating, Refrigerating and Air-Conditioning Engineers) ventilation design standard – which is aimed at comfort, not disease control, so is much lower than that needed to remove infectious aerosols adequately. It also noted that a review of air quality in schools in 13 countries found poor ventilation was common.

The pandemic has stimulated governments in many countries to provide more funds for schools to improve hygiene. The Lancet report highlighted that this provides a once-in-a-generation opportunity to make health-based improvements to school buildings, including to indoor air quality. Preventing the spread of airborne diseases and reducing pollution in schools are part of the same problem. Improvements in indoor air quality will both reduce the risk of children and staff catching airborne diseases and also reduce indoor air pollution, which will provide the benefits of improved health and academic performance. 

Why classroom air quality is important for children

Schools in towns and cities are subject to high levels of pollution in the surrounding area. A study by the London local government found that 98% of schools in London were in areas exceeding WHO pollution limits for PM2.5, the more damaging size of particulates, compared to 24% outside London. Unicef UK estimated in 2018 that one in three children were growing up in areas with high levels of particulates, totalling 4.5 million children in towns and cities. This is repeated in many towns and cities around the world with high levels of traffic and industry.

Poor indoor air quality is caused by numerous pollutants coming from both outdoor and indoor sources. These include volatile organic compounds (VOCs) such as formaldehyde, benzenes, nitrous oxide, carbon dioxide, radon, particulate matter (PM1.0, PM2.5, PM10), fungi (including mould spores), bacteria and viruses (carried in dust and respiratory aerosols), pollen, dust mites and even human skin particles. Vehicles congregate in front of the building at certain times of the day. Schools also use many types of products in teaching, such as art and science materials, that are sources of pollution.

Different populations, different individuals and all of us at different ages react differently to toxins and allergens in the air. It’s been known for decades that some people are hypersensitive to low levels of indoor air pollution or sick building syndrome – the specific causes of which have still not been fully clarified by research. It’s thought to be caused by exposure to low levels of multiple pollutants, which makes the need for good-quality indoor air more important, to keep pollutant levels as low as possible.

Children are particularly vulnerable to air pollution because their bodies are still developing. Younger children, especially, have an underdeveloped or compromised immune system. While children are still growing, their lungs are larger in proportion to their body size. Children also breathe more rapidly than adults so that, relative to their blood volume and body size, their intake of toxins is greater and they absorb a greater concentration of pollutants.

There is a relationship between exposure to indoor pollutants and the development of respiratory symptoms and asthma among people who have not been sensitised before and those who are prone to allergies. Children are more likely to be susceptible while they’re young and growing. Children who have been exposed to high levels of air pollution are also susceptible to chronic diseases later in life. 

Small children spend more time close to the floor because of their height and activities, making them more exposed to pollutants in dust settled on the floor and disturbed by classroom activities –  especially their own. These pollutants can include dust mites, pet allergens, fungal spores, pollen and plant debris, soil and industrial and vehicular particulates brought in from outdoors. A range of synthetic organic compounds, including pesticides, can accumulate in dust. Small children ingest around 100–200 mg/day of dust, about 2–4 times the quantity of adults.

Research by the Swiss Federal Laboratories for Materials Science and Technology (EMPA) has shown a clear link between poor ventilation in classrooms and high numbers of COVID-19 infections. This shows poorly ventilated classrooms (measured by CO2 sensors) had six times the number of cases of COVID-19. This implies that poor classroom ventilation will also have an impact on other airborne respiratory diseases in children.

The effects of air quality on academic performance

Research over decades has shown that poor indoor air quality in schools has a variety of effects on children’s health, ability to learn and academic performance. The wide-ranging, long-term health effects of pollution are well known and include lung diseases, cardiovascular disease, myocardial infarction, heart failure, neurological disorders, diabetes and cancer. 

The effects of poor air quality are not always obvious and include headache, fatigue, coughing, sneezing, dizziness, nausea, irritation of eye, nose, throat or skin. These have a direct effect on the academic performance of children and teachers and attendance at school.

The US EPA reviewed the scientific evidence on the impact of air quality on academic performance and classified studies according to their findings.

• Higher outdoor ventilation (by HVAC or opening windows) in classrooms gave higher scores on standardized tests in maths and reading.
• Improved indoor air quality (IAQ), either by removal of pollution or higher ventilation rates, is linked to faster and improved performance of children.
• Poor physical condition of a building is linked to higher absenteeism and dropout rates.
• A survey of teachers in two areas in the US found that the most frequently cited problem affecting teaching quality was poor IAQ.
• Causes of pollution most frequently associated with respiratory problems such as asthma, include moisture damage, animal and biological allergens, NO2, moisture or dirt in HVAC systems, low ventilation rate, formaldehyde, cleaning products, outdoor pollutants and vehicle exhaust. In the US, nearly one in 13 children has asthma, which is the leading cause of school absenteeism caused by a chronic illness.
• Higher ventilation rates reduce the transmission of infectious diseases and reduce rates of respiratory diseases.
• Control of temperature and relative humidity to keep children in a comfort zone has the most positive impact on mental tasks requiring concentration.
• Airborne or surface dust affects health in schools.

How can schools improve air quality?

Schools have some unique aspects that can make managing air quality more difficult than buildings such as offices. A typical school can have four times as many people as office buildings per unit floor area, which will require higher rates of ventilation. School budgets have been under strain in many countries, with maintenance often facing the largest cuts. 

Multiple factors make managing air quality in schools a high priority for ensuring the health and wellbeing of students and staff and the educational performance of the students. The pandemic has given a rare opportunity to solve the problem of chronic underventilation in schools and focus on improving air quality. Many countries are now taking action by allocating significant budgets to improve indoor air quality. 

There are several measures schools can take to improve indoor air quality.

• Mechanical ventilation with an HVAC system. Often these have not been designed to have sufficient ventilation or filtration rates for airborne diseases and may need “topping up” by using portable air cleaners in rooms. They also need to be maintained to perform adequately.
• Natural ventilation by opening windows where outdoor pollution levels are not going to negatively impact the air indoors and the outdoor air temperature difference won’t affect comfort indoors. 
• Portable air cleaners with HEPA 13 filters. These filter particulates, including respiratory aerosols, and VOCs from the air (but not CO2, which will require ventilation). They should have a clean air delivery rate (CADR) to give a minimum of five air changes per hour (ACH) in the room.