The Government Says

Monitoring air quality and dust on the HS2 Phase One route (October 2025)

Monitoring air quality and dust on the HS2 Phase One route (October 2025)
Local copy of BC_AirQuality_Monthly_Report_October_2025_Optimized.pdf

https://www.gov.uk/government/publications/monitoring-air-quality-and-dust-on-the-hs2-phase-one-route-october-2025

seen at 14:34, 14 January in Policy papers and consultations.