What is air pollution?
Outdoor air pollution includes particulate matter (PM2.5 and PM10), nitrogen oxides (NOx), ozone (O3), volatile organic compounds (VOCs) and ammonia (NH3).
NOx generally comes from road and non-transport, energy industries, and manufacturing, and is generally a local issue near the source.
Perhaps most surprisingly, transport only contributes around 12% of the PM2.5 that we are exposed to, Meanwhile, residential homes, small commercial units, and industry are major sources.
The World Health Organization (WHO) acknowledge that a safe level for PM2.5 is currently unknown, but their guidelines recommend that an annual mean concentration of 10 µg/m3 should not be exceeded1.
PM2.5 can in fact be a very regional pollutant – that is, where pollution caused in one country can be blown by wind into other countries.
Indoor air pollution is also an issue as both households and the workplaces contain hundreds of pollutants including PM2.5 and VOCs.
Studies of human exposure to air pollutants by the U.S. Environmental Protection Agency indicate that indoor levels of pollutants are generally 2 to 5 times higher than outdoor levels2.
Air pollution and health.
Indoor and outdoor air pollution are responsible for 6·5 million deaths worldwide per year, and this figure will continue to rise without urgent intervention.
In the UK, Public Health England estimates that human-made air pollution causes up to 36,000 deaths per year3. In England, the total cost estimate to the NHS and social care between 2017 and 2025 could be as high as £5.6 billion4 with 2.5 million new cases of disease by 2035.
Air pollutants cause adverse effects in adults and children, and is linked to respiratory problems5,6, cardiovascular issues7,8, type-2 diabetes9, foetal growth10, low birth weight11, fertility rate12, dementia13, neuro-behavioural function14 and depression15,16.
Children are particularly vulnerable to the harmful effects of exposure to air pollution because they breathe a greater volume of air per minute than adults (relative to their size), and their lungs are still developing17.
A recent comprehensive review of outdoor air quality around schools by the Air Quality & Public Health Group, Public Health England (PHE) summarises the impacts of poor air quality outside schools on children’s health.
Children with asthma are particularly vulnerable to particles from diesel vehicles. Other conditions impacted by pollution in school outdoor environments include eczema, allergic rhinitis, obesity, increased blood pressure as well as impacts on cognitive performance.
Air pollution around schools.
A recent comprehensive review of outdoor air quality around schools by the Air Quality & Public Health Group, Public Health England (PHE), describes how children encounter pollution peaks on the school journey, at school gates, and in school playgrounds18.
Unsurprisingly, nearby traffic was the key determinant of concentrations in school grounds, as well as outside schools. And the link is multifactorial, with proximity of traffic to the school, density, and traffic flow being major contributors.
Other key factors include planning and urban design (such as the amount of surrounding green space), and structures (such as playground paving).
Morning and evening rush hour traffic contributes strongly to pollution levels outside schools. Diesel vehicle drop-offs and idling outside school are a key contributor to pollution levels.
A study by The Times Newspaper in 2019 estimated that every school in London, as well as around 6,500 other schools in England, exceed the WHO PM2.5 annual mean guideline19.
Furthermore, a report by UNICEF highlights evidence that children in around 2,000 UK schools and nurseries are being exposed to illegal and unsafe levels of NO220.
The PHR report shows how monitoring data in and around schools is limited. Critically, they highlight that open access and high-resolution data for schools was lacking for areas outside London. This suggests that predicted estimates of the number of UK schools with high exposure levels might be well be severely underestimated.
The impact of COVID-19.
Despite the tragic outcomes of the COVID-19 pandemic across Wales, the lockdown period beginning in March 2020 provided a snapshot of how reductions in traffic on our roads might impact on air pollution levels.
Some interesting and quite different patterns emerged, which add to the debate on exposure at schools. It is well documented by Think Air and others that levels of NO2 fell significantly in Wales immediately after lockdown restrictions were introduced due to the huge reduction in traffic21.
Research by Think Air and the Welsh Government showed however that PM2.5 levels across Wales increased during the same period. The likely reasons were that people were spending more time at home and burning more through domestic burners and garden. Furthermore, famers were spreading slurry at this time across the UK and beyond.
We established that PM2.5 can be a very regional pollutant – where pollution caused in one country can be blown by wind into other countries.
The patterns during COVID-19 therefore highlight that reducing traffic on roads is only part of the solution. Indeed, strategies to reduce air pollution outside schools will only go so far in reducing a child’s exposure to PM2.5 as many particles breathed in and around school actually come from much further afield.
The surprising truth.
And this problem could apply to all schools – in both urban and rural areas. As an example, throughout 2020, we monitored air pollution in real-time at a rural village primary school in Garnant, Carmarthenshire – one of the largest counties in the UK but has no real-time air quality monitors22 [web site link – OUR WHITE PAPER]. Our data shows that PM2.5 levels at this rural school were extremely similar each day to Cardiff City Centre. On a number of days throughout the year, PM2.5 levels were higher at the school compared to Cardiff. Our modellers also showed that particulates at the school were being blown from as far afield as Germany and Poland. Other studies are few but have shown that rural sites can have higher PM2.5 in winter while urban school sites are more polluted in spring23.
Air pollution and the school run.
The UNICEF report also highlights how children can experience high particulate peaks on the school run. Interestingly, a study by the BBC in 2019 showed that drivers inhaled levels of PM2.5 44% higher than the WHO guideline.
Pedestrians on the other hand inhaled concentrations at 40.1% above limit, whereas cyclists were 28.1% over the limit24.
This evidence suggests that children who are brought to school by car are exposed to higher levels of particulates than if they walked and there are further benefits to cycling to school or indeed being transported on the back of a bicycle25.
Air pollution inside schools.
Air pollution, of course, isn’t just confined to outdoors. Adults can spend around 87% of their time indoors, with the remainder of their time spent in vehicles (6%) and outdoors (7%)26.
Children on the other hand spend almost 30% of their life in schools and about 70% of their time inside a classroom during school days27. After the home, the classroom is the second most important indoor environment for children.
Whereas sources of air pollution often come from outside a school, the same pollutants can significantly impact on the air quality inside the building. This is because both NOx and PM2.5 can easily pass-through open windows and doors as well as penetrate through buildings.
The SINPHONIE project was the first large-scale pilot study, carried out across 23 European countries, to monitor indoor air quality in schools and found that around 67% of schools are affected by nearby traffic28.
Some schoolchildren and teachers can be exposed to increased levels of benzene and formaldehyde as well as high levels of moulds and bacterial endotoxins. Children are also exposed to other air pollutants including VOCs, which come from many materials such as paint, building materials, cleaning or teaching products17.
But it is not just noxious gases or particulates that can impact of the health and wellbeing of a child in the classroom. Chronic exposure to high levels of atmospheric carbon dioxide (CO2) can have a wide range of health effects such as inflammation, bone and kidney composition changes, respiratory acidosis as well as behavioural and physiological changes29.
Average CO2 concentrations in offices, schools and homes typically range from 600-1000 parts per million (ppm) but can often exceed 2000 ppm with increased room occupancies and reduced building ventilation rates.
To ensure compliance with Regulation 6 of the Workplace Regulations on Ventilation, the Department for Education (DfE) have set performance standards for teaching and learning spaces where, if mechanical ventilation systems are used, the maximum CO2 concentration should not exceed 1500 ppm for more than 20 consecutive minutes each day when the number of room occupants is equal to, or less than the design occupancy30.
In schools with natural ventilation, the average daily concentration should be less than 1500 ppm, during the occupied period, when the number of room occupants is equal to, or less than the design occupancy.
A typical classroom with 30 pupils and 2 staff corresponds to a CO2 level of around 1000 ppm under steady state conditions with an outdoor air ventilation rate of between 8 and 9 litres per second person.
Do the current guidelines protect children from negative health impacts of CO2?
The SINPHONIE study also revealed that ‘occupation densities’ in around 20% of all schools are lower than 2m2 per child leading to increased levels of CO2 in classrooms. A recent review by Northwestern University, Chicago, details how levels of CO2 at around 1000 ppm, previously considered ‘normal’ and safe, can actually be harmful to physical and mental health29.
Furthermore, these levels can impact on cognitive function and thus our ability to think and perform. Work by the Royal Aberdeen Children’s Hospital has shown how inadequate classroom ventilation where CO2 concentration exceeded 1000 ppm is not uncommon and may be associated with reduced school attendance31.
The SINPONIE study also suggested that there is also an interplay between CO2 levels in the classroom and particulate matter. Limiting CO2 levels to below 1000 ppm and thermal conditions below current guidelines can result in airborne particulate matter concentrations being maintained below the recommended annual WHO guidelines and can thus improve indoor air quality.
Are children aware of air pollution?
A YouGov poll carried out in April 2021 by the cycling charity Sustrans showed that out of 1,305 children, aged six to 15, nearly half (49%) said that they were worried about the issue32.
That was a 10% increase on the number of concerned children from a similar poll in 2018.
Around 40% of pupils thought that the best way to bring down levels of air pollution near their school was for more people to walk, cycle, or scoot to school.
Nearly 60% of pupils described the environment around their school as having too many cars and around 30% of pupils are ‘worried’ or ‘sad’ that private vehicle use, especially cars, makes more greenhouse gases in the UK than anything else.
Whereas only 2% of the children polled currently cycle to school, seven times that number said that they now want to reduce air pollution.
Air pollution and the media.
There has been much media attention following the publication of the coroner’s report into the tragic death in 2013 of nine-year-old Ella Adoo-Kissi-Debrah who lived near the South Circular Road in Lewisham33.
An inquest into Ella’s death found that air pollution ‘made a material contribution’ to her death. Ella was the first person in the UK to have air pollution listed as a cause of death on their death certificate.
Critically, in his report, the coroner highlighted that parents don’t know where to look for information on air pollution, and called for more information on its impact to be made available to the public.
A recent paper published by Think Air and K-Sharp on Google Trends analysis of searches for air pollution showed that daily public interest in air pollution strongly mirrors media attention such as that of BBC News34.
Our work shows that public interest in air pollution has increased gradually over the last decade, but to change human behaviour there needs to be greater information provided on a regular basis.
A major driving force for installing our Think Air network of PM2.5 monitors across Wales is to help determine where those particles are coming from – as well as to allow all people, including children, parents and teachers to know particulate levels in their area.
Our PM monitoring network data in Wales has already shown that it is simple and cost-effective to monitor air pollution outside schools in urban and rural areas. Our monitors also help inform teachers, parents, and children about the air quality around them. In turn, this data can help drive positive behavioural change to reduce air pollution, and improve both the health and wellbeing of the next generation.
1WHO Air quality guidelines for particulate matter, ozone, nitrogen dioxide and sulfur dioxide, WHO, 2005 (accessed 21/04/2021)
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12 Xue T and Zhu T. Environ Int. 2018, 121(Pt 1):955-962
13 Peters R. et al. J Alzheimers Dis. 2019, 70(s1):S145-S163.
14 Salvi A. et al. Front Neurosci. 2019, 21;13:1232.
15 Gładka A. et al. Int J Occup Med Environ Health. 2018, 31(6):711-721.
16 Buoli M. et al. Environ Int. 2018, 118:154-168.
17 RCP, 2016. Every Breath We Take: the Lifelong Impact of Air Pollution. Report of a working party. https://www.rcplondon.ac.uk/projects/outputs/every-breath-we-take-lifelong-impact-air-pollution.
18 Osborne S, Uche O, Mitsakou C, Exley K, Dimitroulopoulou S. Air quality around schools: Part I – A comprehensive literature review across high-income countries. Environ Res. 2021 Jan 30;196:110817.
19 R. Watts. Air Pollution on Streets Is Poisoning 2.6m Schoolchildren
20 H. Edwards, A. Whitehouse, J. Grigg. The Toxic School Run: UK Children at Daily Risk from Air Pollution (2018). https://downloads.unicef.org.uk/wp-content/uploads/2018/09/UUK-research-briefing-The-toxic-school-run-September-2018.pdf?_ga=2.50215907.47165167.1566484207-1823034711.1561476036
22 [web site link – OUR WHITE PAPER].
23 Mainka A, Zajusz-Zubek E, Kaczmarek K. PM2.5 in Urban and Rural Nursery Schools in Upper Silesia, Poland: Trace Elements Analysis. International Journal of Environmental Research and Public Health. 2015; 12(7):7990-8008.
25 Jette Rank, Jens Folke, Per Homann Jespersen, Differences in cyclists and car drivers exposure to air pollution from traffic in the city of Copenhagen, Science of The Total Environment, Volume 279, Issues 1–3, 2001, 131-136, ISSN 0048-9697.
26 Klepeis NE, Nelson WC, Ott WR, Robinson JP, Tsang AM, Switzer P, Behar JV, Hern SC, Engelmann WH. The National Human Activity Pattern Survey (NHAPS): a resource for assessing exposure to environmental pollutants. J Expo Anal Environ Epidemiol. 2001 May-Jun;11(3):231-52.
27 Zs. Bakó-Biró, D.J. Clements-Croome, N. Kochhar, H.B. Awbi, M.J. Williams, Ventilation rates in schools and pupils’ performance, Building and Environment, Volume 48, 2012, 215-223, ISSN 0360-1323.
28 Csobod, E., Annesi-Maesano, I., Carrer, P., Kephalopoulos, S., Madureira, J., Rudnai, P., De Oliveira Fernandes, E., Barrero, J., Beregszászi, T., Hyvärinen, A., Moshammer, H., Norback, D., Páldy, A., Pándics, T., Sestini, P., Stranger, M., Taubel, M., Varró, M., Vaskovi, E., Ventura Silva, G. and Viegi, G., SINPHONIE – Schools Indoor Pollution and Health Observatory Network in Europe – Final Report, EUR 26738, Publications Office of the European Union, Luxembourg, 2014, ISBN 978-92-79-39407-2.
29 Jacobson, T.A., Kler, J.S., Hernke, M.T. et al. Direct human health risks of increased atmospheric carbon dioxide. Nat Sustain 2, 691–701 (2019).
30 BB 101: Ventilation, thermal comfort and indoor air quality 2018
31Gaihre S, Semple S, Miller J, Fielding S, Turner S. Classroom carbon dioxide concentration, school attendance, and educational attainment. J Sch Health. 2014 Sep;84(9):569-74. doi: 10.1111/josh.12183. PMID: 25117890.
32 Sustrans: Increase in children’s concerns over air pollution