The significance of vehicle emissions standards for levels of exhaust pollution from light vehicles in an urban area G.A. Rhys-Tyler a, * , W. Legassick b , M.C. Bell a a Transport Operations Research Group, School of Civil Engineering & Geosciences, Newcastle University, Claremont Road, Newcastle-upon-Tyne NE17RU, United Kingdom b Southwark Council, London SE1P 5LX, United Kingdom article info Article history: Received 26 July 2010 Received in revised form 13 March 2011 Accepted 14 March 2011 Keywords: Remote sensing Vehicle exhaust emissions London Nitric oxide Emissions standards abstract This paper addresses the research question “Are more stringent exhaust emissions standards, as applied to light vehicle type approval, resulting in reduced vehicle pollution in an urban area?” The exhaust emissions of a sample of over fifty thousand road vehicles operating in London were measured using roadside remote sensing absorption spectroscopy techniques (infrared and ultraviolet), combined with Automatic Number Plate Recognition for vehicle identification. Levels of carbon monoxide (CO), hydrocarbons (HC), nitric oxide (NO), and smoke (particulate) exhaust emissions are reported by vehicle class, fuel type, and Euro emissions standard. Emissions from petrol cars of each pollutant were all observed to display a statistically significant reduction with the introduction of each successive Euro emissions standard from Euro 1 onwards. However, Euro 2 diesel cars were observed to emit statistically higher rates of NO than either Euro 1 or Euro 3 standard diesel cars. The study also confirms the continuing ‘dieselisation’ of the UK passenger car fleet. Mean NO emissions from Euro 4 diesel cars were found to be 6 times higher than Euro 4 petrol cars, highlighting the need to develop a sound under- standing of the current and future ‘in-use’ emissions characteristics of diesel vehicles, and their influence on local air quality. Smoke emissions from TXII London taxis (black cabs) were found to be statistically higher than either earlier TX1 or later TX4 model variants, with possible implications for local air quality policy interventions such as maximum age limits for taxis. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction Atmospheric pollutants have been the subject of regulation through national and international legislation for a number of years. The European Union has recently adopted Directive 2008/50/ EC on ambient air quality and cleaner air for Europe, consolidating previous legislation, which sets out limit values for a range of pollutants considered harmful to human health. These include limit values for nitrogen dioxide (NO 2 ) and particulates (PM 10 ). In Lon- don, United Kingdom, NO 2 and particulates are the two main pollutants of concern within the Mayor’s Air Quality Strategy (Greater London Authority, 2010). Most particulate emissions come from road transport (engine emissions, and tyre and brake wear). Road transport and heating systems are the main sources of NO 2 . The Mayor’s Air Quality Strategy notes that whilst NO 2 is of most concern due to its impact on health, the control of total NO x (NO 2 þ NO) is essential because of the ease with which nitric oxide (NO) converts to NO 2 in the atmosphere. The European Union has adopted increasingly stringent regu- lations to control the composition of exhaust emissions within the vehicle type approval process, because of the significance of road transport as a source of air pollution. Current European vehicle type approval legislation regulates levels of NO x (oxides of nitrogen) in exhaust emissions, but not specifically NO 2 , an apparent disconti- nuity in European regulatory policy highlighted by Carslaw and Beevers (2004). This issue has become more significant in the UK in recent years because of the increasing proportion of diesel fuelled passenger cars in the UK fleet. In the UK, 33% of new passenger cars registered in 2004 were diesel; in 2009, this percentage increased to 41% (DoT, 2010). Diesel (compression ignition) engines tend to produce higher levels of NO x and partic- ulates compared to petrol (spark ignition) engines. Diesel engines also emit a higher proportion of their NO x as NO 2 compared with petrol engines (Alvarez et al., 2008). Vehicle manufacturers have utilised a range of exhaust treatment technologies to achieve compliance with the increasingly stringent type approval limits. However, researchers such as Carslaw (2005) and Grice et al. (2009) * Corresponding author. Tel.: þ44 191 222 5458; fax: þ44 191 222 6502. E-mail address: glyn.rhys-tyler@newcastle.ac.uk (G.A. Rhys-Tyler). Contents lists available at ScienceDirect Atmospheric Environment journal homepage: www.elsevier.com/locate/atmosenv 1352-2310/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.atmosenv.2011.03.035 Atmospheric Environment 45 (2011) 3286e3293