Risks of exceeding the hourly EU limit value for nitrogen dioxide resulting from increased road transport emissions of primary nitrogen dioxide

Abstract In London, the recent analysis of ambient measurements has shown that directly emitted (primary) nitrogen dioxide ( NO 2 ) has increased as a fraction of total nitrogen oxides ( NO X ) from road transport sources. These increases appear to be mostly due to certain after-treatment devices, such as oxidation catalysts and particle filters fitted to diesel vehicles. This study uses a constrained simple chemical model to predict hourly concentrations of NO 2 at a busy roadside site in central London to investigate the dependence of peak hourly concentrations of NO 2 on the level of assumed primary NO 2 emitted by road vehicles. The model performance is shown to be good across the full range of hourly NO X and NO 2 concentrations over seven years. Monte Carlo simulations are used to predict future hourly NO 2 concentrations and the probability of exceeding the EU hourly limit value for NO 2 by considering the model errors, uncertainties in future NO X trends and the inter-annual variability of meteorology. It is shown that if the NO 2 / NO X emission ratio of 22.0% by volume, as calculated at the end of 2004, is sustained into the future, it is likely that the hourly EU limit value will not be met. However, the probability of not meeting the limit value in 2010 depends strongly on the meteorological year and varies from 16% to 88% depending on the year considered. This work shows that further increases in the NO 2 / NO X ratio beyond those observed at the end of 2004 would considerably increase the probability of the EU hourly limit for NO 2 being exceeded. Additionally, the analysis of road network emissions in London shows that many other roads are likely to be at risk from exceeding the hourly limit value. Further work is required to improve the quantification of NO 2 in vehicle exhausts to determine the likely future risks of exceeding the hourly limit value in other European cities.

[1]  D. Carslaw.  Evidence of an increasing NO2/NOX emissions ratio from road traffic emissions , 2005 .

[2]  Alberto Ayala,et al.  Diesel and CNG Heavy-duty Transit Bus Emissions over Multiple Driving Schedules: Regulated Pollutants and Project Overview , 2002 .

[3]  Christoph Hueglin,et al.  Long-term observation of real-world road traffic emission factors on a motorway in Switzerland , 2006 .

[4]  David C. Carslaw,et al.  Estimations of road vehicle primary NO2 exhaust emission fractions using monitoring data in London , 2005 .

[5]  Scott C Herndon,et al.  Mobile laboratory with rapid response instruments for real-time measurements of urban and regional trace gas and particulate distributions and emission source characteristics. , 2004, Environmental science & technology.

[6]  David C. Carslaw,et al.  Investigating the potential importance of primary NO2 emissions in a street canyon , 2004 .

[7]  S. Beevers,et al.  Development of an urban inventory for road transport emissions of NO2 and comparison with estimates derived from ambient measurements , 2005 .

[8]  Robert Henry Hammerle,et al.  Performance of a catalyzed- diesel particulate filter system during soot accumulation and regeneration , 2003 .

[9]  Mark Z. Jacobson,et al.  The effect on photochemical smog of converting the U.S. fleet of gasoline vehicles to modern diesel vehicles , 2004 .

[10]  M. Jenkin.  Analysis of sources and partitioning of oxidant in the UK—Part 2: contributions of nitrogen dioxide emissions and background ozone at a kerbside location in London , 2004 .

[11]  C. A. McHugh,et al.  Use and validation of ADMS-Urban in contrasting urban and industrial locations , 2000 .