Estimates of the distribution of different fractions of PM10 in the ambient air in the Netherlands

This report presents some methods to synthesize the present knowledge into a comprehensive overview. Several assumptions sometimes of a more or less speculative nature had to be introduced to arrive at a complete picture. These assumptions have been mentioned explicitely as 'seven rules of thumb'. Using these rules, two statements i.e. 1) the ratio between Dutch and foreign contributions to PM10 levels is 20% and 80% and 2) a local contribution of 15% of primary PM10 by Dutch sources, are shown to contradict. As a way of hypothesis generation a contribution of 40% to 45% by local Dutch sources to PM10 levels is presented. This difference can be accounted for by assuming a larger share of local emissions of coarse particles > 2.5 mum to PM10 concentrations than was estimated previously. PM10 concentrations for five areas of the Netherlands are estimated using the seven rules, simple model calculations and assumptions on concentration gradients caused by differences in source characteristics and size distributions. It appears that the original 'blanket' of homogeneous PM10 concentrations covering the Netherlands, indicating rather small concentration gradients, turns out to be more like a 'patchwork quilt'. The estimated concentration ranges are comparable with the ranges of annual PM10 concentrations of 35 - 45 mug/m3 , measured by the National Air Quality Monitoring Network