The Government Says

Monitoring air quality and dust on the HS2 Phase One route (March 2026)

Monitoring air quality and dust on the HS2 Phase One route (March 2026)

https://www.gov.uk/government/publications/monitoring-air-quality-and-dust-on-the-hs2-phase-one-route-march-2026

seen at 10:31, 29 June in Policy papers and consultations.