UK Urban NO2 Network


The UK Urban NO2 Network (UUNN) is an air quality monitoring network that provides measurements of nitrogen dioxide (NO2) concentrations at urban traffic sites. NO2 measurement data provided by the UUNN is used to assess compliance against the annual mean NO2 limit value set out in the Air Quality Standards Regulations (2010).

The network was first established in January 2020 with 177 measurement sites and was expanded to 300 sites from January 2021.

What is the aim of the UUNN?

The primary aim of the UUNN is the provision of NO2 monitoring data for the assessment of compliance with the annual mean NO2 limit value under the Air Quality Standards Regulations (2010), alongside measurement data from the Automatic Urban and Rural Network (AURN), and national scale modelling from the Pollution Climate Mapping (PCM) model.

How is the monitoring done?

The UUNN is delivered by Bureau Veritas under contract with the Environment Agency. The network uses Palmes-type diffusion tubes that are modified to include a wind protection cap in order to improve data quality. The tubes are deployed in triplicate at each monitoring location to reduce the level of uncertainty, and therefore increase the level of accuracy, associated with each monitored concentration. The data from the network is validated using monitors co-located with continuous analysers on the AURN network.

Where are the monitoring sites?

UUNN measurements are located in areas where Local Authorities are working with the Defra/Department for Transport Joint Air Quality Unit (JAQU) or the Devolved Administrations to reduce NO2 concentrations in line with the UK plan for tackling roadside NO2 concentrations.

UUNN monitors are sited specifically to target areas where modelling has indicated an exceedance of the annual mean NO2 limit value, and where there are differences in the concentrations predicted by Defra’s PCM model and by local modelling.

Out of the 300 sites in operation since January 2021, 38 sites are co-located with AURN continuous analysers to provide colocation monitoring data for validating monitored NO2 concentrations.

More information

More detailed information on the network can be found in the UUNN Annual 2020 Report:

Data measured by the network can be downloaded from the Annual Statistics section of this website, and can be viewed on the interactive monitoring map.  It is also available to download on the compliance map and data hub.

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