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Chemical composition of particulate matter calculated

Issue 02-04-2013A VITO study commissioned by MIRA provides insight into the dispersion of the various chemical fractions of particulate matter. While the model gives a fairly reliable assessment of the total mass of particulate matter, accurate model calculations for the composition of particulate matter remain problematic. The study shows that primary particulate matter of local origin appears to account for a rather substantial share of the total mass.

The current belEUROS model produces an accurate assessment of the total mass of particulate matter (PM10 and PM2.5). To obtain this total mass, the model calculates the underlying chemical reactions which result in the total particulate matter mass. It is important to know this concentration, because it is a determining factor for the degree of harmfulness to health. Moreover, the composition of particulate matter helps us locate its origin. Earlier studies by VMM provide detailed temporal and spatial information about the composition of particulate matter based on measurements.

Measurements are inadequate to obtain a more accurate overall picture of the chemical composition of particulate matter. For this purpose, modellings are used in which the various particulate matter fractions are calculated on the basis of airborne emissions and chemical reactions. This makes it possible to generate area-wide information with larger, subsequently selected, time intervals.

In this study report, steps are taken to optimise the belEUROS model so that not only the total mass but also the chemical composition can be calculated. There is, however, still a great degree of uncertainty surrounding the results and the model does not as yet allow any final conclusions to be drawn. Especially the assessment of concentrations of directly emitted (primary) components remains problematic, probably because of the gaps in the emission data on which the calculations are based, e.g. resuspension of road dust, wood combustion.

Local emissions nevertheless appear to have a major effect on the elementary carbon (EC) fraction at locations and on days with high total particulate matter concentrations. Elementary carbon is one of the most harmful fractions to health. Because of the local origin of this pollutant, it is also possible for (local) policy makers to take specific action. The model's assessment of the secondary components is slightly better, but here too the results should be interpreted with due caution. Because the share of secondary components results mainly from emissions over a greater distance (e.g. foreign emissions), this does somewhat qualify the high share of imported particulate matter in the annual average total mass in earlier reports.

Read the English summary of the Dutch report ‘Model optimisation for chemical sub-components of the belEUROS model’

Study commissioned by MIRA, the Environment Reporting Unit
Research report MIRA/2013/02 - VITO/2013/RMA/R/49

researchers: Felix Deutsch, Jean Vankerkom, VITO en Jordy Vercauteren, Myriam Bossuyt, Frans Fierens, VMM

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