Diesel
Diesel vehicles emit higher levels of NOx and particulates than new petrol vehicles. They generally have lower CO2 exhaust emissions compared to petrol, because of the higher efficiency of diesel engines. However the overall climate change benefit may be negligible once refinery emissions and emissions of other climate change pollutants, such as black carbon, are taken into account.
Petrol
Petrol vehicles produce less local air pollution with their lower NOx and particulate emissions. Some new petrol technologies now coming onto the market offer significant improvements in fuel efficiency. Compare fuel economy and CO2 figures for petrol and diesel models to see what the differences are.