Variability of air pollutants, and PM composition and sources at a regional background site in the Balearic Islands: Review of western Mediterranean phenomenology from a 3-year study.

The present study discloses the results of a comprehensive 3-years campaign (2010-2012) of air pollution measurements over an regional island background area (Can Llompart-Balearic Islands, Spain), contextualized with other measurements in the western Mediterranean region. Gaseous pollutants and particulate matter fractions were measured in real time; and PM10 and PM1 daily samples were obtained regularly from which chemical analyses were performed. Furthermore, during three intensive observation periods, real-time concentrations of particle number, black carbon and ammonia were additionally measured. Our results display particular diurnal and seasonal patterns for certain pollutants such as O3 and particle number concentration. Our study reveals that concentrations of air pollutants and aerosol chemical composition are rather similar all over the central and western Mediterranean basin. The most abundant chemical components in PM10 were mineral dust, followed by organic matter, sea spray and SO42-; in PM1 organic matter and SO42- dominated, with significant contribution of mineral dust. Furthermore, a source apportionment Positive Matrix Factorization analysis was conducted. Natural sources exert most of the impact on the coarse-mode fraction, while most of fine-mode aerosols are linked to anthropogenic sources coming from local, regional or long range transport emissions. Prevalence of Atlantic air masses in 2010 had a positive effect in air quality, lowering mineral dust, SO42- and EC concentrations. On the contrary, the high incidence of African dust and regional recirculation situations during the 2012 warm season favoured an overall PM load increase governed by mineral dust, SO42- and trace elements associated to dust aerosols. The continuous increase in tourists in the Balearic Islands, and in general all around the Mediterranean, is clearly changing air quality patterns: while urban air pollution has strongly decreased since 2010, such downward trend is less pronounced at the regional scale, thus related to crescent sources such as maritime and air transport.