This study uses a combination of data from U.K. monitoringstations and from modelling undertaken with the U.K.Meteorological Office''s NAME Model to investigate therelative influences of primary and secondary particulateson total PM10 levels at sites in the United Kingdom. Co-located PM10 and sulphate aerosol measurementsindicate that sulphate has a disproportionately largeinfluence on the variation of PM10 levels incomparison to its contribution to their total mass.Comparisons of measured PM10 at urban centre, roadsideand rural sites suggest that local primary sources havevery little influence on daily mean levels. NAME has beenused to model both primary particles and sulphate aerosolfrom sources across the whole of Europe. The discrepanciesbetween modelled and observed PM10 suggest that coarseparticles, such as windblown dust and resuspended roaddust,may comprise a very large, if not dominant, proportion ofobserved PM10 levels. The apparently minor role ofprimary particles (especially locally-sourced ones) raisesa number of issues regarding the suitability of current U.K.and European legislation to addressing the particle problem.