The Government Says

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

Monitoring air quality and dust on the HS2 Phase One route (July 2026)
Local copy of BC_AirQuality_Monthly_Report_July_2026.pdf

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

seen at 10:37, 14 October in Policy papers and consultations.