Trucks and vans fitted with transport refrigeration units (TRUs) add around 11% more CO2 emissions compared with standard vehicles without TRUs on-board, which amounts to an estimated total of 5,600-plus kilotonnes of CO2.

The findings come from an interim report from Zemo Partnership, which also reveals that calculations for emissions of ultrafine particles resulting from the use of TRUs has been revised upwards compared with the original analysis.

Ultrafine particles pose a particular health concern where vehicles operate close to where people live and work. 

The study finds that emissions of fine particulate matter and other local pollutants of concern, including NOx and larger particulates, are much higher for vehicles fitted with auxiliary TRU engines, with the large majority of pollutants - especially fine particulates - emitted by the TRU engine rather than the drive powertrain of the vehicle. 

The report’s central estimate is that the refrigerated road vehicle fleet adds over 5,600 kilotonnes (kt) of CO2 to total road transport emissions, of which over 80% comes from refrigerated HGVs, with the remainder from refrigerated vans. 

Original research for this study calculated that an additional 54 kt of tailpipe CO2 emissions come from the refrigeration systems on vans compared with those without a fridge. These vehicles also consume around 20 million litres of extra fuel - 0.3% of the total fuel burned by vans. 

A final stage of the report, due to be completed later this winter, will assess alternative technologies to reduce emissions from TRUs on-board vehicles as fleets transition away from operating on diesel. 

Zemo project manager Emily Stevens said: “This latest research confirms that there is a significant issue in terms of emissions arising from the presence of refrigeration units on vehicles, particularly in terms of their impact on local air quality. 

“The final stage of the study aims to provide further evidence and useful recommendations for operators and policymakers to reduce their negative impacts.” 

The research is part of a multi-year project funded by the DfT which aims to understand the UK-wide environmental impact of auxTRUs and other non-road mobile machinery (NRMM). It builds on previous work undertaken between Zemo Partnership and Transport Scotland in 2021.

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