Elsevier

Atmospheric Environment

Volume 45, Issue 19, June 2011, Pages 3286-3293
Atmospheric Environment

The significance of vehicle emissions standards for levels of exhaust pollution from light vehicles in an urban area

https://doi.org/10.1016/j.atmosenv.2011.03.035Get rights and content

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 understanding 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.

Highlights

► Euro standards have a significant influence on light vehicle tailpipe emissions. ► Petrol car NO, CO, HC, and smoke are reduced progressively from Euro 1 to Euro 4. ► NO emissions from Euro 2 diesel cars are statistically higher than Euro 1 and 3. ► Mean NO from Euro 4 diesel cars are 6 times higher than from Euro 4 petrol cars.

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 (NO2) and particulates (PM10). In London, United Kingdom, NO2 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 NO2. The Mayor’s Air Quality Strategy notes that whilst NO2 is of most concern due to its impact on health, the control of total NOx (NO2 + NO) is essential because of the ease with which nitric oxide (NO) converts to NO2 in the atmosphere.

The European Union has adopted increasingly stringent regulations 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 NOx (oxides of nitrogen) in exhaust emissions, but not specifically NO2, an apparent discontinuity 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 NOx and particulates compared to petrol (spark ignition) engines. Diesel engines also emit a higher proportion of their NOx as NO2 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) have highlighted the significance of diesel particulate filters, and other exhaust after treatment systems for diesel engine vehicles, in the increasing formation of primary NO2, and a subsequent increase in the local NO2/NOx ratio due to road traffic.

Given the dynamic nature of the UK vehicle fleet, and the significance of the environmental challenges facing policy makers, there is relatively little detailed current information available in the literature about the ‘in-use’ environmental characteristics of road vehicles in the UK. Some studies were carried out in London in the 1990’s measuring carbon monoxide (CO) and hydrocarbons (HC) (Sadler et al., 1996, Muncaster et al., 1996, Revitt et al., 1999), using roadside remote sensing, but both instrumentation and fleet characteristics have evolved over the intervening period. A European Joint Commission Services Study into ‘In-use vehicle emission controls’, carried out in 1994–1998, included roadside remote sensing measurements at a number of locations, including two locations in the UK. The study assessed the effectiveness of remote sensing as a method of screening the vehicle fleet for high emitters (Barlow, 1998). The EU FP5 REVEAL project developed a low cost roadside remote sensing device (RSD) to collect data on overall car fleet emissions characteristics and gross emitters, which included a field trial in London in 2003 (REVEAL, 2004). The REVEAL RSD was later used in Winchester, UK in 2006 to research driver motivation for voluntary vehicle emissions related maintenance (Felstead, 2007).

Ropkins et al. (2009) provide a comprehensive critical review of the techniques utilised to monitor real-world vehicle exhaust emissions. Real-world measurements (measurements of exhaust emissions from vehicles in operation on the highway network) differ from laboratory based measurements (typically using test cycles) because they have a more realistic potential to capture the range of variability typically encountered in real-world driving, including variability in driver behaviour, interactions with other road users, and interactions with highway infrastructure, all of which have the potential to influence exhaust emissions. Real-world measurements using techniques such as remote sensing also have the potential to monitor a representative cross section of vehicle ages and levels of maintenance (including faulty vehicles), sampling many thousands of vehicles, which would not be practical or cost effective to attempt in laboratory conditions. The disadvantages of remote sensing in this context relate to the variability in ambient atmospheric conditions, variation in size and location of exhaust plume, and limitations on the levels of absolute accuracy achievable in practice using such methods. Remote sensing can be seen as a useful complement to more detailed measurements using laboratory based chassis dynamometers or engine test beds, or on-road instrumented vehicles. Other researchers have identified its potential to provide statistically robust fleet emission characteristics through repeat measurements over a sustained period of time (McCrae et al., 2005).

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 paper explores the exhaust emissions characteristics of a large sample of vehicles operating in London, UK in 2008, based on data collected using roadside remote sensing absorption spectroscopy techniques (infrared and ultraviolet), combined with Automatic Number Plate Recognition (ANPR) for vehicle identification, and vehicle speed/acceleration measurement. Using this information, the ‘in-use’ emissions characteristics of the observed vehicles can be determined, by vehicle class, fuel type, vehicle age, and other parameters. Vehicle age is used as a proxy to classify the observed vehicles by Euro emissions standard. This information facilitates the estimation of the relative environmental impact of each vehicle category by Euro emissions standard for each atmospheric pollutant, allowing policy makers to evaluate the real-world effectiveness of increasingly stringent vehicle exhaust emissions standards. The research has the potential to inform the development of air quality improvement strategies, including possible interventions such as vehicle scrappage incentive schemes, and access restrictions to localities with air quality problems for certain categories of high polluting vehicles.

Section snippets

Source of data

The analysis utilises a pre-existing raw dataset supplied by colleagues at Southwark Council and Ealing Council, UK. The data were collected in 2008 using an RSD 4600 on-road vehicle emissions testing device manufactured by Environmental Systems Products, operated under contract by Enviro Technology Services (Merelles, 2008). The development and application of this equipment and measurement technique is described extensively in the literature (Bishop et al., 1989, Burgard et al., 2003, Burgard

Exhaust emissions characteristics of the observed light vehicles

Table 1 presents a summary of observed light vehicle exhaust emissions by vehicle class, fuel type, and emissions standard, where data sample bins contain generally more than 100 observations. Mean and median values are presented for measured CO (%), HC (ppm), NO (ppm), and smoke number. The divergence of mean and median values in the data is indicative of the presence and influence of large values in the tails of the distribution of data. Previous studies have identified the skewed and

Conclusions

The objective of this paper was to address 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 paper explored the exhaust emissions characteristics of a large sample of light vehicles operating in London in 2008, based on data collected using roadside remote sensing techniques. Whilst remote sensing has some limitations in terms of the levels of absolute accuracy

Acknowledgements

This work was part funded by the EPSRC FUTURES project and Newcastle University. The authors are grateful to colleagues at Southwark Council and Ealing Council for the supply of data, and we acknowledge with thanks the role of Transport for London in the original data collection project. The authors wish to acknowledge the assistance of Dr Linda Davies at Imperial College for help with documentation, and to Dr Neil Thorpe at Newcastle University for useful comments on the text. We are also

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