Variations of urban aerosols in the western Mediterranean

Real time measurements of number concentrations (13-800 nm, N13-800) of size discriminated sub-micrometric aerosols and PM (0.3-10 mu m) mass concentrations were carried out over a one-year-period at an urban site in Barcelona. North-eastern Spain. Annual mean levels of N13-800 were close to 17,000 cm(-3), and strongly dependent on road traffic emissions. Annual mean PM10, PM2.5 and PM1 levels were 39, 25 and 18 mu g/m(3), being highly influenced not only by road traffic but also by industrial emissions as well as natural events such as African dust outbreaks. Variability of number concentrations and size distribution of sub-micrometric aerosols was strongly dependent on meteorology. Primary emissions exert a high influence on the variability of levels of ultrafine (<100 nm) particles under intense Atlantic advections (lowest PM levels), while coagulation and condensation processes are enhanced under urban pollution scenarios (highest levels of PM), and photochemical nucleation processes can be an important source of ultrafine particles at midday in summer (low PM levels). African dust episodes did not modify the total number but affected the N > 400 nm. This study allows us to compare aerosol number and mass concentrations in air quality monitoring of an urban environment. Ultrafine particles measurements are indicated to detect the variability of primary traffic emissions, as well as some atmospheric processes. Measurements of PM levels are necessary to monitor other important PM sources in the studied area such as dust resuspension from road traffic or African dust. (C) 2008 Elsevier Ltd. All rights reserved.