The Government Says

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

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

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

seen at 14:38, 9 September in Policy papers and consultations.