The Evolution and Control of NOx Emissions from Road Transport in Europe

Abstract

Road transport is the largest contributor to NOx emissions in the EU. This chapter discusses NOx formation mechanisms, control strategies, trends in emissions and possible future developments. Control strategies include vehicle emission legislation, engine design, exhaust after-treatment, modification of fuel properties, alternative fuels and new powertrain technologies. Calculations show that NOx emissions from the sector decreased substantially between 1990 and 2010. Such calculations are based on the assumption that the systematic tightening of emission limits has been effective. However, there is evidence that modern diesel vehicles are not delivering the expected reductions in emissions during real-world driving. Moreover, diesel vehicles emit more NOx than petrol vehicles (with a larger proportion of “primary” NO2), and their market share has increased in many countries. These factors partly explain the observation that ambient NO2 concentrations continue to exceed health-based limits in urban areas. Up to 2020 there is a need for a more effective regulation of emissions, and the chapter proposes several measures that can be taken. Beyond 2020 emissions of NOx from the sector will depend on the market penetration of low-carbon technologies.