The UK Urban NO2 Network (UUNN) 2024

The UUNN was first established in January 2020 and has expanded since to respond to evidence needs and is currently operating at ~299 sites.<br/>The primary aim of the UUNN is the provision of additional NO2 monitoring data for inclusion within the national UK compliance assessment. Previously the national assessment of NO2 has comprised of a UK-wide automatic monitoring network; the Automatic Urban and Rural Network (AURN), and national scale modelling; the Pollution Climate Mapping (PCM) model.<br/>UUNN monitors were sited specifically to target areas where modelling had indicated an exceedance of the annual mean NO2 limit value, and where concentrations predicted by the PCM model and by local modelling completed by a relevant local authority were not in good agreement.<br/>The two requirements to identify specific road links for UUNN measurements within these areas were originally as follows:<br/>

• Where the PCM model and/or modelling completed by a relevant local authority had predicted an exceedance of the NO2 annual mean limit value of 40µg/m3 in 2020 and/or 2021.<br/>
• Where the difference between the PCM model and modelling completed by a relevant local authority is larger than 20%.<br/>The Network continues to evolve, and now the aims are move generalised benefits rather than the original aims, although the limit of annual mean exceedance of 40µg/m3 is still a key reporting marker.