Trends in hydrocarbon fleet emissions at four UK highway sites

The on-road hydrocarbon emissions of vehicles at four sites in the UK have been monitored using remote sensing equipment. The single lane highway sites in London (Haringey and Southwark), Middlesborough and Leicester were monitored between May 1994 and October 1995. Analysis of the results shows that there is both a large majority of low emitting vehicles which contribute little to fleet hydrocarbon emissions and a small minority of high emitting vehicles which contribute significant proportions to fleet hydrocarbon emissions at all sites. This also results in a skewing of the data set so that a pattern of high mean values and lower median values is consistently observed. Analysis of model year data suggests a low association between vehicle age and mean hydrocarbon emissions for vehicles produced prior to 1983 but the relationship improves after 1983 with regression analyses giving r2 values as high as 0.96. Relatively new high polluting vehicles are the greatest contributors to fleet emissions with, on average, 52% of hydrocarbon fleet emissions being produced by these vehicles from model years 1985-1991. Therefore, fleet emissions could be significantly reduced if new highly polluting vehicles were subject to regular emissions testing followed by appropriate remedial action or were removed from the highway by the withdrawal of their vehicle registration. Older vehicles play a minor role in fleet emissions with, on average, only 13% of hydrocarbon fleet emissions being produced by vehicles registered prior to 1983.