Elsevier

Atmospheric Environment

Volume 41, Issue 7, March 2007, Pages 1343-1358
Atmospheric Environment

Estimated long-term outdoor air pollution concentrations in a cohort study

https://doi.org/10.1016/j.atmosenv.2006.10.020Get rights and content

Abstract

Several recent studies associated long-term exposure to air pollution with increased mortality. An ongoing cohort study, the Netherlands Cohort Study on Diet and Cancer (NLCS), was used to study the association between long-term exposure to traffic-related air pollution and mortality. Following on a previous exposure assessment study in the NLCS, we improved the exposure assessment methods.

Long-term exposure to nitrogen dioxide (NO2), nitrogen oxide (NO), black smoke (BS), and sulphur dioxide (SO2) was estimated. Exposure at each home address (N=21 868) was considered as a function of a regional, an urban and a local component. The regional component was estimated using inverse distance weighed interpolation of measurement data from regional background sites in a national monitoring network. Regression models with urban concentrations as dependent variables, and number of inhabitants in different buffers and land use variables, derived with a Geographic Information System (GIS), as predictor variables were used to estimate the urban component. The local component was assessed using a GIS and a digital road network with linked traffic intensities. Traffic intensity on the nearest road and on the nearest major road, and the sum of traffic intensity in a buffer of 100 m around each home address were assessed. Further, a quantitative estimate of the local component was estimated.

The regression models to estimate the urban component explained 67%, 46%, 49% and 35% of the variances of NO2, NO, BS, and SO2 concentrations, respectively. Overall regression models which incorporated the regional, urban and local component explained 84%, 44%, 59% and 56% of the variability in concentrations for NO2, NO, BS and SO2, respectively.

We were able to develop an exposure assessment model using GIS methods and traffic intensities that explained a large part of the variations in outdoor air pollution concentrations.

Introduction

We recently reported an association between cardiopulmonary mortality and long-term exposure to traffic-related air pollution in a random subgroup of 5000 of a cohort study of elderly people (NLCS study; N∼120 000) (Hoek et al., 2002a, Hoek et al., 2002b). Other recent studies also found associations between long-term exposure to air pollution and health effects (Nafstad et al., 2004; Filleul et al., 2005; Finkelstein et al., 2004).

Two large cohort studies in the US also showed associations between long-term exposure to air pollution and mortality. However, in the Harvard Six Cities study and the American Cancer Society (ACS) study, exposure has been estimated as the average concentration within a city/metropolitan area, ignoring small-scale variations within cities (Dockery et al., 1993; Pope et al., 1995). Exposure studies have shown large variations in concentrations of traffic-related air pollutants on a small scale within cities (Fischer et al., 2000; Jerrett et al., 2005a). A study by Jerrett et al. (2005b) in a subpopulation of the ACS study suggested that the chronic health effects associated with intraurban gradients in fine particles may be even larger than previously reported associations across metropolitan areas.

In our previous study, long-term exposure to traffic-related air pollution was therefore considered as a function of the regional background, an urban background and an indicator variable for living near a major road (Hoek et al., 2001). Following on this previous study, we conducted a study on the association between long-term exposure to traffic-related air pollution and mortality in the full NLCS cohort of ∼120 000 subjects (NLCS-AIR study). In this new study we improve the exposure assessment compared to the previous study that had no traffic intensity data and a less-accurate road network.

The purpose of this paper is to describe an improved method for the assessment of long-term outdoor air pollution concentrations in a cohort study.

Section snippets

Design

The design of the Netherlands Cohort Study on Diet and Cancer (NLCS) (van den Brandt et al., 1990) and the exposure assessment method used in the previous study have been described in detail elsewhere (Hoek et al., 2001). Briefly, the NLCS started in September 1986 when 120 852 participants from 204 municipalities, spread out over the Netherlands, were enrolled. The residential address of all participants in 1986 is known.

The NLCS was designed as a case–cohort study, i.e. mortality cases are

Regional component

We evaluated ordinary kriging and inverse distance weighed interpolation as methods to estimate regional background concentrations at the home addresses. However, there was only a limited number of BS sites (9 sites in the period 1992–1996), and therefore it was not possible to develop a suitable variogram for kriging. Further, the RIVM has used kriging procedures to decrease the density of the network during the rearrangement of the network in 1986. Therefore, it was less possible to estimate

Discussion

We described an improved method to estimate long-term outdoor air pollution concentrations in a Dutch cohort study. Using comprehensive data from existing air pollution monitoring stations, data on land use, population density, road networks and traffic density, we were able to develop exposure assessment models that explained a large part of the spatial variance in long-term averaged air pollution concentrations.

Conclusion

An improved method for assessment of long-term outdoor air pollution concentrations taking into account small-scale variations in air pollution concentrations was illustrated. Despite the limitations and methodological problems, we were able to develop an exposure assessment model using GIS-methods and traffic intensities that explained a large part of the variations in concentrations outdoor air pollutants and which can be used in epidemiologic studies to estimate air pollution levels at

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