Small area variations in ambient NO2 concentrations in four European areas
Introduction
Spatial variations in urban air pollution are of considerable significance both because of the growing evidence for associations between exposure and human health (Dockery et al., 1993; Committee on the Medical Effects of Air Pollution, 1995; Committee of the Environmental and Occupational Health Assembly of the American Thoracic Society, 1996), and because of the increasing requirement for action to control and reduce levels of air pollution. Traffic-related pollution is a particular concern. Levels of road traffic in urban areas have risen markedly in recent decades and emissions of traffic-related pollution have increased accordingly, notwithstanding improvements in engine design and changes in fuel composition (Quality of Urban Air Review Group, 1993; Eurostat, 1995; Department of Transport, Environment and the Regions, 1997a, Department of Transport, Environment and the Regions, 1997b). Road traffic thus accounts for a major proportion of atmospheric pollution in urban environments (Royal Commission on Environmental Pollution, 1994). An understanding of small area variations in traffic-related pollution is therefore essential not only as a basis for exposure assessment as part of epidemiological investigations, but also to help identify pollution `hot-spots’ and other areas in need of specific intervention, and to guide traffic management and other policy development and analysis.
Relatively few attempts have so far been made to examine variation in traffic-related air pollution at the small area scale, despite the fact that this is often the more relevant scale for epidemiological analysis and the scale at which much policy intervention operates. Those which have done so have often demonstrated a high degree of spatial variation at the street or neighbourhood scale, reflecting the complex patterns of emissions and dispersion which occur in urban environments (Hewitt, 1991; Laxen and Noordally, 1987; Monn et al., 1997; Morawska et al., 1999; Väkevä et al., 1999). This paper presents and discusses results of an analysis of small area variations in traffic-related air pollution in four urban centres in Europe: Amsterdam (Netherlands), Huddersfield (UK), Poznan (Poland) and Prague (Czech Republic). Specifically it aims to quantify the components of small area variation in NO2 (as a marker for traffic-related pollution) in a range of contrasting urban environments, and consider the implications for exposure assessment and policy. The research described here represents one part of a larger, EU-funded study of small area variations in air quality and health (SAVIAH), details of which have been reported elsewhere (Briggs et al., 1997; Elliott and Briggs, 1998; Elliott et al., 1995; Fischer et al., 1998; van Reeuwijk et al., 1998).
Section snippets
Study location
The surface area of the four study centres varies from ca. 25 km2 (Amsterdam) to 300 km2 (Huddersfield). The study areas vary in topography and land use. That in Amsterdam is a flat, urban inner-city area with roads of varying traffic density bordered by high-rise blocks of houses. The Huddersfield area comprises a mixture of generally low-rise residential, commercial, industrial and rural land; it has an altitude range of 80–582 m, with much of the built-up land concentrated in the valleys.
Results
Table 1 presents the distribution of the NO2 concentrations over the four surveys in the four study areas. The table shows significant (p<0.001) variation in ambient NO2 levels between surveys, as can be expected due to differences in meteorological conditions and, perhaps, traffic flows during the sampling periods. Concentrations tend to be highest in winter months (survey 2 or 3), possibly reflecting the lower temperatures and mixing heights during these periods. In Amsterdam, for example,
Discussion
In recent years, the use of passive samplers has increased considerably, both for routine monitoring of air pollution (e.g. the UK national passive sampler survey) (Bower et al., 1991; Campbell et al., 1994) and for purpose-designed campaigns run by local authorities or as part of epidemiological investigations (Boleij et al., 1986; Alm et al., 1998). Nevertheless, several studies have raised doubts about the accuracy of passive samplers, for example due to the uncontrolled effects of
Acknowledgements
The SAVIAH study, of which the research was part, was a multi-centre project, funded under the EU Third Framework Programme. It was led by Prof. Paul Elliott (Department of Epidemiology and Public Health, Imperial College, London UK – formerly at the London School of Hygiene and Tropical Medicine) and co-principal investigators were Prof. David Briggs (Nene Centre for Research, Nene University College Northampton, UK – formerly at the University of Huddersfield), Dr. Erik Lebret, Ph.D.
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