A variety of factors impact the average NO2 concentrations in a given area, including meteorological changes and fluctuations in background pollution. In addition, diffusion tube monitoring can lead to variable results which may report large over or underestimates.
This means that readings are more accurate when averaged over a year, a process referred to as ‘annualised bias-adjustment’.
It is only when the results have been subject to this process, that they can then be compared to the air quality objectives listed below. The UK has two national objectives for NO2:
- The annual mean concentration of NO2 to not exceed 40 μg m-3.
- The 1-hour mean to not exceed 200 μg m-3.
The annual mean concentration is calculated using data collected on a monthly basis. There is no UK standard for monthly NO2 concentrations.
We are committed to transparency, which is why we are sharing this monthly data with residents. However, it should be treated with caution. The data provided only shows the laboratory results which have not yet been subject to corrections in accordance with London Local Air Quality Management Technical Guidance. Therefore the data is subject to change and we are unable to draw conclusions until this adjustment process has taken place.
Brent’s air quality monitoring network
Brent has an extensive network of air quality monitoring. This network uses both diffusion tubes, as well as 24hr air quality monitoring stations which provide more in depth data for a range of pollutants.
You can find more information about this existing network of air quality monitoring.
In order to monitor the Healthy Neighbourhoods in Brent, extra air quality data is being collected by installing an extended network of diffusion tubes across Brent. These ultimately will be able to provide an annual mean NO2 concentration for the area as per the existing network outlined above.