Monitoring of sources and atmospheric processes controlling air quality in an urban Mediterranean environment

Different monitoring parameters (PM mass concentrations, number–size distribution, black carbon, gaseous pollutants, and chemical composition, among others) are currently used in air quality studies. Urban aerosols are the result of several sources and atmospheric processes, which suggests that a single monitoring technique is insufficient to quantitatively evaluate all of them.This study assesses the suitability of a number of monitoring techniques (PM mass concentrations, number and size distribution of ultra-fine particles, levels of gaseous pollutants, and a complete chemical characterization of PM10 and PM2.5) by examining the response of those techniques to the different emission sources and/or atmospheric processes affecting an urban Mediterranean area (Barcelona, NE Spain).The results of this work reveal that the PM mass, the number concentration and the chemical composition give different, but complementary, information. Whereas the mineral matter, a key atmospheric aerosol component across the Mediterranean, is not properly quantitatively assessed by measuring sub-micrometric particles, the monitoring of the number concentration is indispensable to interpret the origin of specific aerosol episodes. Furthermore, the chemical composition yields very relevant information to deduce the causes of specific pollution episodes.The number concentration of ultra-fine particles in urban areas is strongly dependent upon vehicle exhaust emissions, which may cause adverse health impacts. Moreover, urban Mediterranean environments are favourable to produce nucleation-mode particles (<20 nm) with photochemical origin. In those cases, these particles are expected to be of high solubility and consequently their toxicity may differ from that of traffic-generated ultra-fine particles. Thus, the use of a single monitoring parameter to evaluate the health effects seems to be not enough.