Air pollution emissions from vehicles as a function of their current real-world market price

This study explores the relationship between diesel and petrol car retail prices and real-world emissions, using data from over 50,000 measurements, collected during a remote sensing campaign in Birmingham, UK. Machine learning was employed to estimate the retail price of the vehicles. The analysis reveals a robust inverse correlation between vehicle price and emissions. Although newer vehicles tend to be more expensive because of their desirability and are cleaner thanks to stricter emissions regulations, the analysis reveals more expensive vehicles typically have lower fuel-specific emission factors (g/kg-fuel), even within the same Euro class. Higher-priced diesels show greater emission reductions than petrols. Results highlight a greater emission reduction potential (per £1000 increase in price) in diesel vehicles (−0.44gNO₂/kg-fuel) compared to petrol (−0.02gNO₂/kg-fuel), though expensive diesels may still emit more NO₂ than cheaper petrols due to inherently higher emissions from diesels. PM emissions in diesel vehicles also decline modestly (−0.03g/kg-fuel), while petrol vehicles show minimal change across price ranges. For diesel vehicles, the drop in emissions as price increases was about 1.5 times greater in older Euro 5 models compared to newer Euro 6 models when measured per unit of fuel used and more than twice as steep when estimated per mile driven. The results highlight a previously overlooked transport-related emission inequality: lower-income individuals are more likely to own cheaper, higher-emitting vehicles, thereby contributing disproportionately to their local urban air pollution. This flips the usual pattern in greenhouse emissions, where wealthy households typically cause more greenhouse gas emissions through their higher consumption.