Abstract

Emissions of NOx are central to a very wide range of atmospheric chemistry problems. It is essential therefore that we have a good understanding of source strengths and how they change with time. This talk will consider the comprehensive analysis of recent trend data from across Europe, with a particular focus on the UK. It is shown that trends in NOx and NO2 concentrations have stabilised across most European countries; particularly in urban areas. The analysis of a large sample of vehicle emissions remote sensing data (ca. 65,000 vehicles) from recent campaigns in the UK show that diesel vehicle emissions from light duty vehicles have changed little over the past 20 or so years; in clear disagreement with inventory projections. The number of diesel vehicles in the vehicle fleet has also increased markedly over the same period. In addition, these vehicles now use exhaust after-treatment technologies that have increased the proportion of NOx that is NO2 from around 10% to nearer to 50%. The evidence for these effects and the wider implications will be addressed.