Probabilistic Modelling of PM2.5 Exposures in the Working Age Population of Helsinki Metropolitan Area Otto Hänninen PROBABILISTIC MODELLING OF PM2.5 EXPOSURES IN THE WORKING AGE POPULATION OF HELSINKI METROPOLITAN AREA

Fine particles are associated with hundreds of thousands annual deaths and significant increase in morbidity in Europe. Improvement of air quality and reduction of air pollution emissions are identified as the primary goals, but environmental policies can be targeted in different ways. It is clear, that optimal protection of public health is achieved by policy options reducing population exposures effectively. Besides air quality and associated temporal and spatial variability, the most important factor affecting exposures is population mobility. In traffic environments the proximity of emissions increases exposures, while in indoor environments concentrations of particles entering from outside are reduced by the building shell. Presence of indoor sources, however, may result in indoor concentrations orders of magnitude higher than outdoors. In the current work a population exposure model was developed to compare the impact of alternative future policy scenarios on population exposures. Comparison with measurements showed that the model predicts the exposures and their variability well. The model errors were smaller than the statistical errors caused by random population sampling in an exposure study, apart from the highest few percentiles. Model applicability to policy evaluation was demonstrated by modelling the potential of ventilation systems equipped with effective particle filters to reduce exposures. Assuming the whole Helsinki metropolitan area building stock would be equipped with such mechanical ventilation systems that is already used in office buildings built in 1990’s, the overall population exposure to ambient particles was reduced by 27 %. This is in the order of the effect of local traffic tailpipe emissions, which would have to be completely removed to achieve a similar net effect. Besides, building ventilation system affects also long-range transported particles. Model correspondence with measurements was good and the model applicability to practical policy options comparison was demonstrated. The general conclusion of the work is that exposure assessment, using models when necessary, should be incorporated with development of effective environmental policies. Subject terms: air pollution, air pollution, indoor, air pollutants, environmental, ventilation, evaluation studies, urban population, particle size