Air pollution from traffic in city districts near major motorways

Abstract

In order to assess exposure to air pollution from traffic of subjects living near motorways, traffic related air pollutants were measured indoors and outdoors in six city districts near motorways in the West of the Netherlands. Outdoor measurements of PM₁₀, PM_2.5, black smoke and benzene were conducted at four different distances from the roadside in two of the six city districts. NO₂ was measured in all city districts. Indoor concentrations of PM₁₀ and NO₂ were measured in 12 schools in the same six city districts. Reflectance of indoor PM₁₀ filters was measured to get an impression of black smoke concentrations indoors. Outdoor concentrations of black smoke and NO₂ declined with distance from the roadside. No gradient was found for PM₁₀, PM_2.5 and benzene. The gradients for NO₂ and black smoke were curvilinear and more evident in periods that the city districts had been downwind from the motorway for at least 33% of the time. PM₁₀ concentrations in schools were high compared to outdoor concentrations and were not correlated with distance of the school from the motorway, traffic intensity and percentage of time downwind. Indoor black smoke concentrations were significantly correlated with truck traffic intensity and percentage of time downwind. NO₂ concentrations in classrooms were significantly correlated with car and total traffic intensity, percentage of time downwind and distance of the school from the motorway.

Introduction

Several recent studies suggest an association between automobile exhaust and increased respiratory symptoms and/or diminished pulmonary function (Nitta et al., 1993; Wjst et al., 1993; Weiland et al., 1994; Oosterlee et al., 1996). In most of these studies the exposure assessment was rather limited. Some studies have used self-reported traffic density on the street of the home address (Weiland et al., 1994; Nakatsuka et al., 1991). Two other studies used modelled nitrogen dioxide (NO₂) concentrations (Oosterlee et al., 1996; Pershagen et al., 1995). One study used density of traffic on the main road through school districts—reported to have a size of about 2 km across (Wjst et al., 1993). Other studies have relied on distance of home address from major roads as measure of exposure (Nitta et al., 1993; Edwards et al., 1994). In one of those studies (Nitta et al., 1993), NO and NO₂ measurements were conducted at 3 or 4 different distances from the roadside at seven locations. Suspended particulate matter (SPM) was measured at 3 distances at one of the locations. Concentrations at the roadside were higher than away from the roadside. In another Japanese study (Nakai et al., 1995), personal, indoor and outdoor measurements of NO₂ were conducted in three zones at different distances from two busy roads 10 times during several seasons. Subjects were selected from participants of a health effects study which was conducted some years earlier. Mean outdoor concentrations were always highest in the zone closest to the road (<20 m) and lowest in the reference zone. Mean personal concentrations were generally higher in the zone closest to the road during nonheating seasons. During the heating seasons this was only the case for residents who did not have an unvented heater.

In 1995, a study was conducted on the respiratory health of children living in six areas near major motorways in the West of The Netherlands (Brunekreef et al., 1997; van Vliet et al., 1997). Exposure to air pollution from traffic was assessed in several ways: distance of home and school from the motorway, traffic density of the motorway and indoor air pollution in schools. This paper describes the air pollution measurements conducted within the framework of this study. The validity of distance from the motorway as a measure of exposure to air pollution from traffic was investigated by conducting outdoor measurements of PM₁₀, PM_2.5, black smoke, benzene and NO₂ at different distances from the motorways. Furthermore, indoor measurements of PM₁₀, benzene and NO₂ were conducted in 12 of the 13 participating schools, to be used as another measure of exposure.