Trends in air pollution between 2000 and 2012 in the Western Mediterranean: A zoom over regional, suburban and urban environments in Mallorca (Balearic Islands)

Particulate matter and gaseous pollutants concentrations (NOx, SO2 and O3) have been measured on a regular basis in several European regions since the beginning of the 90’s. Based on these long-term series of air pollutants, the study of trends over certain European regions has been reported. In the context of the Balearic Islands, more than a decade of uninterrupted measurements at multiple locations has provided, for the first time at an insular location in the Western Mediterranean Basin, the opportunity to study the interannual tendencies and the variability of different air quality metrics. Hourly data of NO, NO2, SO2, O3 and PM10 from 2000 to 2012 were compiled and validated. The monitoring sites were classified in urban, suburban, and rural (or regional) background. The selection of the monitoring sites considered in the trend analysis was done according to two essential criteria: 1) the annual data coverage should be over 75%; and 2) at least 8 of the last 10 years of data exists. Furthermore, the origin of air masses was daily computed, which is a useful way to account for long-range transport of pollutants or to address the occurrence of meso-scale atmospheric processes. Daily, weekly, seasonal and inter-annual patterns of these pollutants have been studied at the different environments. The multi-year and multi-pollutant study, over three environments from the same region, together with the discrimination per air mass origins permitted us to follow those changes induced by the implementation of regional policies and those related to the enactment of continental strategies. Up to now some clear results have been obtained. NO and NO2 undergo clear decreasing trends in urban stations (-1.1 μg/m3year), less evident in suburban and regional background stations (from no change to -0.3 μg/m3year). The behaviour of O3 is opposite to that of NOx at urban stations (+1.0 μg/m3year), almost parallel to the decrease in NO, one of its main depletion agents. At rural background sites O3 shows a moderate increasing trend (+0.5 μg/m3year), consistent with the observations in other European regions. Significant decreasing O3 concentrations are patent at the suburban background (-0.4 μg/m3year), probably caused by an increasing vehicular traffic over these areas. Finally, a substantial decline in PM10 is obvious at urban and suburban (-0.7 μg/m3year) areas, slightly lower over the regional background (-0.5 μg/m3year).