Assessment of PM2.5 levels in the UK uses direct monitoring alongside air quality modelling. We have a network comprising 163 direct monitoring sites providing near-real-time data to our UK-AIR website: https://uk-air.defra.gov.uk. Of these, 77 monitor PM2.5. Modelling of PM2.5 is reviewed regularly to take account of changes in sources of emissions to ensure accurate measurement.
Defra provides technical and policy guidance to local authorities to assist them in meeting their air quality management responsibilities including air quality monitoring and assessment. Defra also provides technical support to local authorities via a dedicated local air quality management Helpdesk (phone, email and webpage).