Elsevier

Atmospheric Environment

Volume 34, Issue 2, January 2000, Pages 177-185
Atmospheric Environment

Small area variations in ambient NO2 concentrations in four European areas

https://doi.org/10.1016/S1352-2310(99)00292-7Get rights and content

Abstract

Spatial variations in urban air pollution are of considerable significance both because of the growing evidence for associations between exposure and human health and because of the increasing requirement for action to control and reduce levels of air pollution. This study examines sources and patterns of variation in NO2, as a marker for traffic-related pollution, in four predominantly urban study areas: Amsterdam (Netherlands), Huddersfield (UK), Poznan (Poland) and Prague (Czech Republic). Data on pollution levels were collected using passive samplers, deployed in duplicate for 2 week periods on four occasions over one year. Mixed-effect modelling was used to explore the magnitude of between-survey, between-site and between-sampler and interaction effects, and to provide a measure of mean annual concentration at each sample site. Measured concentrations varied significantly between different surveys, with a tendency to be higher in winter months. Strong correlations were seen, however, between monitored concentrations in successive surveys, suggesting that the geographic pattern of variation in all areas was essentially stable over time. Between-sampler variation was seen to be small (CV generally 5–8%), indicating that the samplers provided consistent measures of NO2 concentrations. There were also strongly significant between-site and site–survey interaction effects. Between-site variation accounted for between 61% (Poznan) and 84% (Prague) of total observed variation; expressed as a coefficient of variation, between-site variation was least in Amsterdam, the smallest and most uniform study area (22%), and greatest in Prague (42%). The modelled mean annual NO2 concentration, derived from the mixed-effect model, gave a good prediction of mean annual concentration measured using passive samplers on a continuous basis, at 8–10 reference sites in each study area (r2>0.85). Based on the modelled results, it appears that WHO and national air quality standards for NO2 will be routinely exceeded at a number of sites in each study area. Given the apparent stability of the pollution surface in each area, these `hotspots’ are also likely to be persistent over time, implying the potential for relatively high risks of chronic exposure in local populations. Overall the results indicate the capability to characterise spatial variation in traffic-related pollution in urban areas using a small number of intensive surveys, with low-cost sampling devices.

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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