Emissions of precursors of particulate matter

Particulate matter in the air consists of primary and secondary particulate matter. Primary particles are emitted directly into the atmosphere. Secondary particles are formed by chemical reactions of gaseous precursors such as NH3, SO2 and NOx. Also (non-methane) volatile organic compounds (NMVOCs) intervene in the formation of secondary particulate matter, albeit to a lesser extent. From these gases or their reaction products, inorganic or organic aerosols can be formed by the formation of new particles or by adhesion to pre-existing particles. Analysis of the chemical composition of particulate matter in Flanders shows that the secondary inorganic fraction resulting from conversions of NH3, NOx and SO2 accounts for 30-40 % of the mass of PM10. The exact share depends, among other things, on the meteorological conditions, the specific location and the import from abroad.