Airborne Fine Particulates in the Environment: A Review of Health Effect Studies, Monitoring Data and Emission Inventories

Airborne fine particles are a mixture of various components and are emitted by different sources. Short-term and long-term epidemiological studies have associated fine particles with adverse health effects, excess mortality, respiratory and cardiovascular diseases. There are indications that the health effects are more associated with the fine fraction of PM10 and with ultrafine particles (< 0.1 μm) than with the coarse fraction. Recently, diesel exhaust and vehicular emissions have been identified in epidemiological studies as important factors for explaining adverse health effects of fine particles; there are also indications for a biological mechanism. For acid aerosols and sulfate particles, a biological mechanism is proposed in the literature, but results from epidemiological studies are not entirely conclusive. Commonly, no threshold is found and a linear doseresponse relationship is proposed. The spatial and temporal distribution of fine particle levels may vary substantially. Low PM10 levels are found in remote areas at about 10 μg m, heavily polluted urban areas may reach 100 μg m on average. PM2.5 (< 2.5 μm in diameter) commonly comprises 60 % of PM10. Fine particles are emitted as primary pollutants and are also formed during secondary processes in the atmosphere, i.e., through the oxidation of SO2, NOx and VOC emissions. Fine particles are modeled deductively and inductively, i.e., via dispersion and receptor models, respectively. Emission inventories are still in an early stage and need careful consideration of adequate emission factors and other assumptions. In urban areas, traffic is usually an important source of fine particles, although locally the situation can be dominated by emissions from local industries. For remote areas, where local sources are absent, regional and transboundary sources may be prevalent. We hypothesize that vehicular emissions and particularly diesel exhaust are likely to be important, if not the major, factors for the adverse health effects associated with fine particles.