Air quality monitoring

There are a range of methods that can be used to monitor air pollutants. Each method has advantages and disadvantages. Regardless of the method, all data should be subject to robust quality assurance and quality control.

In Ealing, air pollution is officially monitored and reported at over 60 locations. Three monitoring techniques are used by London Borough of Ealing Council to monitor air quality.


Photo of an automatic monitoring sensor

Automatic monitoring

Automatic air quality monitoring stations (automatic monitors) are the most sophisticated air quality monitoring systems. The data is corrected, maintained, and calibrated on a regular basis to ensure it is accurate and reliable. Automatic monitors draw in air and measure the concentration of the pollutant in the sample air which can then be communicated to the public in near-real time via websites such as this one. In Ealing there are currently four automatic monitoring stations all measuring nitrogen dioxide (NO2) and particulate matter (PM10). Check out the latest and historic data.

To ensure that data produced are accurate and reliable, a high standard of operation is required, including operator training, regular maintenance, calibrations and detailed quality assurance/quality control measures. As a result, automatic monitoring is a relatively expensive option compared to the techniques below.

Photo of a low cost air quality sensor

Sensor monitoring

Lower-cost air quality sensors are typically small, low power devices which can be powered by battery, solar energy or electricity from a lamppost column. Whether installed on streetlights, buildings or even handheld for mobile pollution studies, these lower-cost sensors provide valuable information on pollutants such as particulate matter (PM10 and PM22.5), nitrogen dioxide (NO2) and ozone (O3). Because of their lower costs compared to automatic monitoring, they can be deployed in larger numbers. However, air quality sensors may not give accurate data immediately, and their initial readings might differ significantly from the actual pollution levels. Regular quality assurance/quality control measures and data correction are essential to ensure reliable and meaningful air quality information.

In Ealing, as part of a Defra Air Quality Grant, there are currently eight lower-cost sensors monitoring air pollution outside schools and a further two sensors in residential streets by means of comparison. Take a look at their latest and historic data.


Passive sampling

This method uses tubes to absorb specific pollutants from the air. In Ealing, diffusion tubes are used for nitrogen dioxide (NO2) monitoring. After the sample is collected, the diffusion tubes are sent to certified laboratories for analysis.

The monthly results are averaged to produce an annual average for each monitoring location. This average is adjusted at the end of the year using a direct comparison of all the monthly averages obtained by diffusions tubes for a year, with the ones obtained by an automatic monitor at a specific location.

Diffusion tubes are deployed at 60 sites across Ealing providing a monthly average. However, they cannot identify high pollution episodes within a day and cannot be used to identify daily trends or short-term air pollution episodes as information on air quality levels arrive a lot later when diffusion tubes are analysed.

Every year Ealing submits annual status report that provides a detailed overview of air quality and it also contains results of diffusion tube monitoring.

Photo of a diffusion tube

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