Abstract
This paper presents an examination of the source signature or origin signature represented by particle number size distributions and modal diameters measured at a rural receptor site in southern England which receives air from a range of polluted and less polluted origins. At this site, particle number size distributions (11-450 nm) with smaller modal diameters (<50 nm) are measured in clean maritime air masses, while particle number size distributions with larger modal diameters (>50 nm) correspond to anthropogenic emissions from local or more remote activities and long range transport. Nucleation mode and aged-nucleation mode particles (mainly from 18 to 33 nm) were mostly new particles from nucleation. Accumulation mode particles (90-120 nm) were associated with aged polluted air masses, two thirds of which arrived from continental Europe. Aitken mode particles had different origins with different signatures. Some of them corresponded to local vehicular emissions and in this case the distributions are typically bimodal. Particle number size distributions with the smallest Aitken modal diameters (around 44 nm) corresponded to background particles in westerly maritime air masses; possibly new particles formed upwind. Particle number size distributions with the largest Aitken modal diameters (around 67 nm) were transported from anthropogenic sources that are thought to be mainly within the UK.