Elemental Carbon and Nitrogen Dioxide as Markers of Exposure to Diesel Exhaust in Selected Norwegian Industries

Abstract

Elemental carbon (EC) and nitrogen dioxide (NO2) in air as markers for diesel exhaust (DE) emission exposure were measured in selected work environments in Norway where diesel-powered engines are in use. Two hundred and ninety personal full-shift air samples were collected in primary aluminium production, underground and open-pit mining, road tunnel finishing, transport of ore, and among airport baggage handlers. EC was determined in the samples by a thermo-optical method, while NO2 was determined by ion chromatography. Highest EC air concentrations (geometric mean, GM) were found in aluminium smelters (GM = 45.5 μg m-3) followed by road tunnel finishing (GM = 37.8 μg m-3) and underground mining activities (GM = 18.9 μg m-3). Low EC air concentrations were measured for baggage handling at an international airport (GM = 2.7 μg m-3) and in an open-pit mine (GM = 1.2 μg m-3). Air concentrations of NO2 were similar in road tunnel finishing (GM = 128 μg m-3) and underground mining (GM = 108 μg m-3). Lower NO2 values were observed in open-pit mining (GM = 50 μg m-3), at the airport (GM = 37 μg m-3), and in the aluminium smelters (GM = 27 μg m-3). Highly significant (P < 0.001) positive correlations between NO2 and EC air concentrations in underground mining (r = 0.54) and road tunnel finishing (r = 0.71) indicate a common source of these pollutants. NO2 and EC were also correlated (P < 0.01) positively at the airport. However, due to the complex air chemistry and a potential contribution of various sources, the correlation between EC and NO2 cannot be regarded as unambiguous hint for a common source. The association between EC and NO2 was not of statistical significance in open-pit mining. In the aluminium smelters, EC and NO2 were negatively correlated, although not reaching statistical significance. The substantial differences in NO2/EC ratios across the investigated industries, ranging from around 0.2 in the primary aluminium production to around 25 during spring at the airport, clearly show that exposure to DE cannot be estimated based on NO2 concentrations, at least for outdoor environments. Results in the primary aluminium production suggest that the measured EC concentrations are related to DE emissions, although the NO2 concentrations were low. Further studies are required to assess the magnitude of exposure in primary aluminium production.