Changes (%) in emissions of primary and secondary PM10 particles by source category, 1990-2007, EEA-32 (weighted by particle formation factors)

The graph shows the emissions of primary PM10 particles (particulate matter with a diameter of 10 μm or less, emitted directly into the atmosphere) and secondary particulate-forming pollutants (the fraction of sulphur dioxide, SO2, nitrogen oxides NOx and ammonia NH3 which, as a result of photo-chemical reactions in the atmosphere, transform into particulate matter with a diameter of 10μm or less).
Emissions of the secondary particulate precursor species are weighted by a particle formation factor prior to aggregation: primary PM10 = 1, SO2 = 0.54, NOx = 0.88, and (NH3) = 0.64