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Nitrogen dioxide monitoring data

Use this page to view nitrogen dioxide (NO2) monitoring data, the location of air quality monitoring sites, and understand our nitrogen dioxide objectives. 

How we monitor nitrogen dioxide

We monitor nitrogen dioxide using automatic (reference) and non-automatic (passive diffusion tubes) analysers. There are approximately 160 monitoring sites with diffusion tubes across the district.

Monitors are located on signposts or lampposts by the roadside or somewhere on the footway. Concentrations of nitrogen dioxide decrease rapidly as you move away from the roadside.

Diffusion tubes

Diffusion tubes are subject to interference from weather that does not affect automatic analysers. To counter this, a bias adjustment factor is applied. 

This is established from study sites where diffusion tubes have been co-located with automatic (reference) monitors.  2021 data will be included when it the final quality assurance and quality control has been carried out.

A site denoted as triplicated is where three tubes are exposed at one location. This is to prevent data loss caused by interference with the tube. This is commonly caused by spiders nested in the tubes. At these locations the three tubes is given.

2014-2022 nitrogen dioxide report

The interactive report below provides information on the following:

  • locations of the air quality monitoring sites in Bath and North East Somerset
  • the annual average nitrogen dioxide monitoring data for 2014-2022 for all monitoring sites in Bath and North East Somerset
  • compliance with the National Government (40 µg/m³) and Local Council (36 µg/m³) nitrogen dioxide objectives