Exposure to motor exhaust in the occupational and general environment in Stockholm county

Abstract

In recent years, health hazards associated with air pollution from motor exhaust have received increasing attention. Lung cancer and heart disease have been linked to air pollution exposure. However, the knowledge concerning exposure levels, is insufficient, but is essential for risk assessment. This thesis is aimed at improving our knowledge about exposure to motor exhaust related air pollutants, particularly in the Stockholm region.

In paper I, nitrogen dioxide (NO2) levels were measured at 42 different sites in the Stockholm area. NO2 concentrations were measured with passive dosimeters during four two-week periods per observation site. Similar measurements were performed in Munich, Germany and in the Netherlands. Season-adjusted mean values varied from 11 to 29 mug/m3 at the different types of sites in Sweden. In the other countries the levels were higher, although street levels in central parts of the cities were similar.

Upon comparison, the passive dosimeter method underestimated the levels in Sweden compared to the reference method, chemiluminescence, for annual mean values, although there was a wide variance for individual measurement periods. Papers II, III and IV investigate occupational exposure to motor exhaust. Paper II is a comparative study of 121 taxi, bus and lorry drivers in the Stockholm region. NO2 was measured using portable passive dosimeters, and particle concentration within the size range 0.1 10 mum was measured with a real-time monitoring light scattering instrument. For both particles and NO2, taxi drivers had the lowest exposure, the lorry drivers the highest and the bus drivers' exposure were in between the others. The group mean exposure concentration varied between 48 and 68 mug/m3 for NO2 and between 26 and 57 mug/m3 for particles.

The number of occupations included as well as the measured indicator substances was expanded in study III. In all 71 subjects were included, divided into 7 groups depending on place of work (indoor, outdoor, vehicle driver) and type of fuel (petrol or diesel). In addition to the indicators used in paper II, particles were measured in the size ranges PM1 (aerodynamic diameter <1.0 mum), PM2.5 (aerodynamic diameter <2.5 mum). A chemical analysis was performed in order to ascertain levels of elementary carbon, EC, and total carbon, TC. Exposure to NO2 and all particle fractions was considerably higher for the group construction workers in road tunnels than for any other group. Many of the other groups showed surprisingly similar exposure levels for both NO2 and particles. Outdoor workers experienced the lowest exposure to NO2 while the driver groups were exposed to the lowest levels of some of the particle fractions. Drivers and outdoor workers were exposed to similar levels of EC, 4 8 mug/m3, indoor workers 11 12 mug/m3, with tunnel workers exposed to 87 mug/m3. All of the observed groups of workers were exposed to higher levels of NO2 than urban background levels in Stockholm.

In conclusion, the work in my thesis demonstrates that it is possible to quantify geographical differences in the concentration of NO2 with a simple method at different types of sites in metropolitan areas. In Stockholm County NO2 levels were three times as high in City streets compared with suburban Järfälla. Our knowledge of occupational exposure to NO2 and particles has been improved through the use of portable measurement equipment by approximately 200 subjects. When subjects working in tunnels were compared with a group of outdoor workers the exposure to NO2 was about 10 times higher while exposure to EC, the fraction that most closely reflects diesel exhausts, was about 20 times higher.