The Government Says

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

Monitoring air quality and dust on the HS2 Phase One route (May 2026)
Local copy of BC_AirQuality_Monthly_Report_May_2026.pdf

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

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