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Air Quality Monitoring at Schools - Does the annual mean give the FULL picture of the real

exposure to air pollution?

Air pollution and children

Air pollution is an evolving problem that has grown profoundly in significance in recent decades

becoming one of the most important threats to human quality of life, not only nationally but on a

global level. Here in the UK, the biggest threat to clean air comes in the form of air pollution

generated by exhaust fumes and other particulate matter given off by traffic. Both petrol and diesel engine vehicles release a wide variety of pollutants, principally oxides of nitrogen (NOx), and particulate matter (PM), which negatively impact air quality, especially in urban areas. Exposure to such pollutants puts local populations at higher risk to their negative health effects, especially those with vulnerabilities.

Children in particular are more susceptible to the harmful effects of air pollution; due to a

combination of physiological, environmental and behavioural factors. According to the WHO, it is

estimated that 93% of the world’s children under the age of 15 years are exposed to polluted air

every day putting their health and development at risk. A recent study published in November 2019, from a partnership between King's College London and Queen Mary University of London, showed that children who were exposed to an average of 40.7 μg/m3 of NO2 over five years had a reduction in their lung volume of approximately 5%. The study highlights the importance of monitoring traffic related air pollution in urban areas and implementing mitigation measures when necessary in order to ensure that children are exposed to as little air pollution as possible.

How we monitor air quality

In the UK, each local authority has been carrying out a review and assessment of air quality in their

district, measuring air pollution to make sure that national air quality objectives set out by the UK

Government are achieved by their deadlines. An Air Quality Management Area (AQMA), can be

declared when a local authority finds that the air quality objectives in that location are not likely to

be achieved. The local authority will then monitor air quality within the newly formed AQMA and

formulate a plan to decrease the higher amounts of air pollution there.

Within an AQMA, there are two main methods of monitoring air quality. Firstly, Automatic Urban

Networks (AURNs), which are large monitoring stations that can deliver very accurate data on local

air pollution levels. However, they are big in size and expensive, and for this reason offer poor spatial resolution which can result in pollution hotspots not being identified. The second method comes in the form of diffusion tubes which are inexpensive to deploy but offer poor temporal resolution as they only measure the average monthly concentrations of an area.

left - Automatic Urban Networks; right - diffusion tubes.

To get around these limitations, local authorities across the country are implementing low-cost air

quality monitors as a means of providing localised data with a good time resolution. Advances in

sensor technology means low-cost monitors can now provide scientifically credible data for detailed air quality assessments. These monitors are compact, easy to deploy and are low-cost to service. They are great at identifying the hyper-local air pollution hotspots and how selected mitigation measures can affect the air quality.

Low cost air quality monitors

Air Quality study at a Primary School – What is the air pollution exposure to children during drop

off and pick up times

A local authority carried out a case study in a primary school in the UK for 7 weeks at the end of 2019 and beginning of 2020. An Aeroqual AQY – Micro Air Quality station1 was deployed on the school’s façade, 5 m from a busy road. The school is situated 50 meters from an Air Quality Management Area (AQMA) and close to a busy junction, which is the only entrance and exit for vehicles accessing a nearby housing estate.

It was observed that during the school drop off (8 to 9 am) and pick up (3 to 4 pm) times, parents parked in front of the school with their engines on, and consequently traffic jams formed along the road. Head teachers were concerned that the traffic formed during these periods would lead to pupils being exposed to significantly higher levels of pollution.

The closest air quality monitoring station is a diffusion tube site, located approximately 75 m from the school within the AQMA. NO2 diffusion tubes measure the average monthly or annual concentrations of an area and cannot provide data for short term events such as school times or drop off and pick up times. The annual mean for this nearest diffusion tube site is shown in the table below and was found to be just under the 40 μg/m3 annual mean air quality target for NO2 as defined by DEFRA.

Data from the study showed that during the period in which the AQY was deployed, the 7 weeks mean for NO2 was 39.43 μg/m3, which correlates well with the diffusion tube data and is below the annual mean as set up by DEFRA. However, this average will include night-time, weekends and regular holiday periods when children were not at school.

Meanwhile, data from the study showed high hourly peaks on weekdays were consistently observed between 8 to 9 am and 3 to 4 pm, as shown in the chart below. In these hourly periods, the mean for NO2 far exceeded 40 μg/m3 with peaks of almost 100 μg/m3. Children arriving or leaving the school at these times were exposed to much higher levels of air pollution, than those recommended by DEFRA.

The chart below shows in blue the NO2 hourly mean throughout the 7 weeks and the red line shows the annual air quality objective. It was observed that the high peaks were consistent with the drop off and pick up times on most of the weekdays. In addition, a few peaks were also observed during the evenings.

As the Aeroqual AQY delivers real-time data, it was possible to calculate the NO2 mean taking into consideration the school’s opening days and hours, as well as the mean for the drop off and pick up times. The data showed that short-term events didn’t exceed the hourly mean objective for this pollutant (200 µg/m3) but the table below shows they were above the annual mean. Studies like the King's College London and Queen Mary University of London mentioned in the beginning of this article, indicate that long exposure to considered low levels of NO2 (40.7 µg/m3) were related to a reduction in the volume size of children’s lungs.

Another parameter evaluated in this study was PM2.5, which is also emitted during the combustion of liquid fuels in vehicles engines. According to DEFRA, only 12% of PM2.5 is from urban traffic, with 45% coming from background pollution. A comparison between the hourly mean for NO2 and PM2.5 below shows that morning peaks for particulates coincide with the start of the school, whilst the afternoon peaks start rising at the end of the school day reaching their highest concentrations much later at around 6 pm. Even so, the annual objective was not exceeded during the school hours. The fine particles only exceeded the annual objective of 25 µg/m3 during New Year’s Eve, likely due to the celebratory fireworks.

In conclusion, it was possible to identify the levels of air pollution which children were exposed to during the school opening hours over the seven weeks of study. The NO2 mean for the monitoring period during drop off (58.60 µg/m3) and pick up times (54.79 µg/m3) exceeded the annual objective for this pollutant, at a concentration considered harmful for young ones. The air quality data provided by the AQY during this case study can help the head teacher and local authorities to implement mitigation measures in order to ensure that children who attend the primary school are exposed to as little air pollution as possible.

Surveys like this one indicate that evaluating the mean for community exposure studies does not give the full picture. The study showed that the area where the school is located is compliant with the annual air quality objective, however the hours the children were at school it was not.

Furthermore, children over 11 years of age spend approximately 50% of their waking time in school. According to the British Suppliers Education, there are 32,770 schools in the UK, including nurseries, primary, middle and secondary schools, receiving more than 10 million pupils. The evidence could suggest a significant proportion of them are likely to be exposed to levels of air pollution that studies show to be dangerous.