Estimations of road vehicle primary NO2 exhaust emission fractions using monitoring data in London

Abstract Hourly mean concentration data for nitrogen oxides (NO X ), nitrogen dioxide (NO 2 ) and ozone (O 3 ) have been used to derive a method for estimating the mean primary NO 2 fraction from vehicle exhausts in London. A set of simple chemical equations has been used to explain the differences in NO 2 concentrations between background and roadside site pairs and to estimate the proportion of NO 2 that is likely to be derived from primary NO 2 vehicle emissions and the NO 2 formed through the reaction of nitric oxide (NO) with O 3 . These results suggest that there is a wide range of primary NO 2 emission fractions observed on different roads in London. The estimates ranged from 3.2 to 23.5 vol% with a median value of 10.6 vol% for the 43 measurement sites considered. A median primary NO 2 fraction of 10.6% accounts for an average of 21% of the observed NO 2 concentration at roadside sites. The range in calculated primary NO 2 fractions explains much of the variation in annual mean NO 2 concentrations between monitoring sites in London. The estimated primary NO 2 fraction is considerably higher than the 5.0 vol% typically used in modelling studies that aim to predict ambient NO 2 concentrations. These results have implications for the assessment of NO 2 concentrations in London and whether London will meet the limit values set by the European Union. Further work is required to explain the wide range of primary NO 2 fractions estimated in terms of road traffic composition and activity.

[1]  John C. Hilliard,et al.  Nitrogen Dioxide in Engine Exhaust , 1979 .

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

[3]  Michael E. Jenkin,et al.  Analysis of sources and partitioning of oxidant in the UK—Part 1: the NOX-dependence of annual mean concentrations of nitrogen dioxide and ozone , 2004 .

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

[5]  Ole Hertel,et al.  Effects of reduction of NOx on the NO2 levels in urban streets , 1996 .

[6]  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 .

[7]  A. Coppalle,et al.  Turbulence effects upon the NO2/NO conversion in the vicinity of an urban area. , 1996, The Science of the total environment.

[8]  S. Beevers,et al.  New Directions: Should road vehicle emissions legislation consider primary NO2? , 2004 .

[9]  Richard J. Brown,et al.  Prediction of short-range maximum NO2 concentrations using scalar PDFS , 2004 .

[10]  The influence of turbulence upon the chemical reaction of nitric oxide released from a ground source into ambient ozone , 1996 .

[11]  M. Jenkin,et al.  Analysis of the relationship between ambient levels of O3, NO2 and NO as a function of NOx in the UK , 2001 .

[12]  Ulrich Platt,et al.  Investigations of emissions and heterogeneous formation of HONO in a road traffic tunnel , 2001 .

[13]  Ruwim Berkowicz,et al.  OSPM - A Parameterised Street Pollution Model , 2000 .