The UK government has paused new funding for selective catalytic reduction (SCR) exhaust retrofits after evidence came to light that the scheme may not be effectively reducing NOx emissions to anticipated levels.
A letter, revealed to routeone following a freedom of information request, dated 19 April and sent from the Department for Transport (DfT) to Birmingham City Council officials explains that the decision has been prompted by “considerable variability in performance” of retrofitted buses.
Authors Claire Wren and Henry Shennan, Directors of Future Transport Systems and Environment at DfT, note: “Our most recent in-service monitoring has highlighted evidence to suggest that the SCR technology on retrofitted buses is not, in the sample studied, reducing NOx emissions to the levels expected.”
DfT has initiated a research programme to investigate the causes behind the underperformance, with findings expected to be released in autumn. While the Clean Air Zone (CAZ) status of already retrofitted buses remains unchanged, the letter advises against making further retrofit purchases until the study has been completed.
The Clean Vehicle Retrofit Accreditation Scheme (CVRAS) is the government scheme supporting the operation of CAZs. Of retrofit solutions for buses, exhaust after-treatment systems combining diesel particulate filter (DPF) and SCR technology are the most widely applied. Representatives from the retrofit segment have questioned the need for the suspension of funding and have criticised the validity of the testing.
Addressing local authorities that have received funding for bus retrofit, DfT assured that its commitment to achieving cleaner air is unwavering. “The UK has a high ambition for domestic air quality, as set out in the Clean Air Strategy and enshrined in the Environment Act 2021 and Environmental Improvement Plan 2023,” the letter reads.
A follow-up meeting will address queries and discuss the potential impacts and mitigation plans specific to each area. In the meantime, local authorities are urged to maintain efforts to achieve legal levels of NO2 through the development and implementation of local air quality plans.
routeone is pursuing this story and expects to publish a full report in the July 2023 issue.
