Temporal and spatial variability of atmospheric particle number size distributions across Spain

This study synthesizes for the first time results from simultaneous aerosol measurements performed at seven diverse locations distributed all over the Spanish geography. The observations were carried out during two field campaigns in 2012-2013, one-month each and during different seasons. These field campaigns were performed in the framework of the Spanish Network of DMAs (REDMAAS) activities. Measurement sites were grouped as polluted sites (urban background) and clean sites (rural background and high-altitude sites). Seasonal differences were more important at polluted sites, mainly related to meteorology and aerosol sources. Higher total particle concentrations were found during the cold period, driven mainly by Aitken-mode particles (traffic-related aerosol particles). In clean sites, particle concentrations were higher during the warm period. Mild meteorological conditions in combination with the absence of local sources during the cold period make atmospheric nucleation an important contributor to ultrafine particles. These results are reflected in aerosol dynamical processes. Ultrafine particle bursts were frequent in both periods at the clean sites and in the warm period at most polluted sites. Shrinkages processes were identified at three sites (two polluted and one clean site) during the warm period. Meteorology (wind speed and solar radiation) and a highly-volatile aerosol (formed from atmospheric nucleation or traffic emissions) explain this behaviour. Ultrafine particles exhibited a different behaviour at inland and coastal sites. The highest total particle concentrations were observed at coastal sites during the warm period. At these sites, the smallest particle modal diameters and the highest variations of particle number size distributions in the smaller particle size range were also found, particularly in the warm period. This may be the result of the high diffusion conditions and mixing of different air masses (clean and polluted) caused by sea-land breezes. Our findings can be explained by the local and regional characteristics of each site, such as meteorology and aerosol sources (types, proximity …) and the influence of meteorology on atmospheric transformation processes.