Small area variations in ambient NO2 concentrations in four European areas

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 contro l and reduce levels of air pollution. This study examines sources and patte rns 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 we re collected using passive samplers, deployed in duplicate for 2 week perio ds on four occasions over one year. Mixed-effect modelling was used to expl ore the magnitude of between-survey, between-site and between-sampler and i nteraction :effects, and to provide a measure of mean annual concentration at each sample site. Measured concentrations varied significantly between d ifferent surveys, with a tendency to be higher in winter months. Strong cor relations were seen, however, between monitored concentrations in successiv e surveys, suggesting that the geographic pattern of variation: in:all area s was essentially stable over time. Between-sampler variation was seen to b e small (CV generally 5-8%), indicating that the samplers provided consiste nt measures of NO2 concentrations. There were also strongly significant bet ween-site and site-survey interaction effects. Between-site variation accou nted 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 t he mixed-effect model, gave a good prediction of mean annual concentration measured using passive;samplers on a continuous basis, at 8-10 reference si tes in each study area (r(2) > 0.85). Based on the modelled:results, it app ears 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 stabil ity of the pollution surface in each area, these 'hotspots' are also likely to: be persistent over time, implying the potential for relatively high ri sks of chronic exposure in local populations. Overall the results indicate the capability to characterise spatial variation in traffic-related polluti on in urban areas using a-small number of intensive surveys, with low-cost sampling devices. (C) 1999 Elsevier Science Ltd. All rights reserved.