Danny has forwarded a link to the 40 page mid-year report from Mendip District Council:
https://www.mendip.gov.uk/media/29448/Air-Quality-Report-2021/pdf/Mendip_DC_ASR_2021.pdf?m=637728237034800000
There’s a map within showing the location of the 7 NO2 monitors in Frome.
The PDF links to this Somerset website:
Which offers this overview:
There is only one automated pollution monitor in Somerset forming part of the national network. It is in rural south somerset, and intended to provide background rural readings.
The only other automated monitors at the moment (2020) are in Bridgwater, located on the major transport routes and checking particulate pollution levels as part of the Hinkley Point C nuclear power station project. Particulate pollution is not currently monitored elsewhere in the county.
All four district councils carry out year round monitoring of nitrogen dioxide at multiple sites. This monitoring is carried out using diffusion tubes which are left in place for a month at a time and then sent off for analysis. The annual mean (average) reading is then calculated for each location. Traffic and weather conditions result in large variations in short term levels of nitrogen dioxide, but these do not exceed the statutory limit.
The Mendip report also has these two notes:
• [Somerset intends to] bring forward proposals for monitoring PM2.5, in order to gain an understanding of where this is problematic in the county. There is a poor understanding of fine particle pollution due to a lack of monitoring to date.
• Mendip District Council have implemented an Anti-Idling campaign which focuses on changing behaviour to discourage unnecessary idling of combustion engine vehicles. There has been a rollout of signage and publicity messaging to this end
