Vehicle emissions are one of a number of environmental problems in urban areas which have received much public attention for nearly twenty years  and are still now very topical. In particular, public opinion in Europe is opposed to the visible smoke, ‘black’ from diesel engines and ‘blue’ from oil burning petrol and diesel engines.This paper describes the use of 90 degree backscatter measurements to determine and measure ‘black’ and ‘blue’ smoke effects in an in-service environment, i.e. no dynamometer or loaded cycle testing. The measurements are compared to opacity measurements and the advantages and disadvantages discussed. White smoke effects will not be addressed in this paper.