UK Urban NO2 Network
Introduction
The UK Urban NO2 Network (UUNN) is an air quality monitoring network that provides measurements of nitrogen dioxide (NO2) concentrations at selected roadside locations. 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 has expanded since, containing 300 sites in 2024.
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.
Note – Due to the strict data capture and data quality levels required for compliance reporting not all UUNN data has been included in the compliance assessment each year.
How is the monitoring done?
The UUNN is delivered by Ricardo 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.
Where are the monitoring sites?
UUNN sites are focused 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 to target areas where local monitoring has indicated an exceedance of the annual mean NO2 limit value to ensure that the national assessment is underpinned by the best available evidence.
Out of the 300 sites in operation in 2024, 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 Reports:
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.