**4. Conclusions**

This study allowed an understanding of the temporal evolution of the air quality during a period of ten years (2003–2012) in Setúbal, an urban area with a high influence of industrial activities. Overall, the air quality index has been improving during the studied period. Setúbal has a set of climate variables, which favors good dispersion of pollutants and, ultimately, confer good air quality in this region despite strong industrial emissions.

With the exception of ozone, all pollutants have demonstrated a decreasing trend, probably due to the implementation of cleaner technologies in the industries, the development of less polluting vehicles; during the study period, the global economic crisis situation also had an impact on the region, which promoted a decrease in production and the closure of some industrial units. However, despite this trend, some pollutants still presented exceedances of the European and WHO guidelines, namely, particulate matter (PM2.5 and PM10), NOx and ozone.

Characterization of PM2.5 and PM10 levels in the area allowed the identification of the main sources contributing to local PM levels, namely, tra ffic, industry and wood burning, which should be addressed by specific mitigation measures in order to minimize their impact on local air quality.

**Supplementary Materials:** The following are available online at http://www.mdpi.com/1660-4601/17/15/5447/s1, Figure S1: Spearman correlations between PM and PM components sampled in the studied monitoring stations: "Quebedo" (urban tra ffic type) and "Mitrena" (industrial type). All elements/ions are displayed in ng·m<sup>−</sup><sup>3</sup> and PM mass concentration is displayed in mg·m<sup>−</sup>3, Figure S2: Contribution of each source to total PM10 mass (top) and total PM2.5 mass (bottom) sampled in the monitoring stations Quebedo and Mitrena, Table S1: Statistical data (yearly mean [minimum-maximum]) of meteorological variables (relative humidity and temperature, with the number of measurements, n) registered in the two meteorological stations during the monitoring period of 2004–2012, Table S2: Air quality limit and target values established by the European Commission's Directive 2008/50/EC [51] and air quality guidelines (AQG) defined by the World Health Organization (WHO) [29].

**Author Contributions:** Conceptualization, A.V.S., S.M.A. and A.I.M.; methodology, A.V.S., S.M.A., A.I.M., C.M.O.; data research and data analysis, A.V.S., C.M.O. and S.M.A.; original draft preparation of the manuscript, A.V.S. and S.M.A.; review of the manuscript, A.V.S., A.I.M., C.M.O., N.C. and S.M.A. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by Fundação para a Ciência e Tecnologia, I.P. (FCT) by the gran<sup>t</sup> project PTDC/AAC-AMB/098825/2008 ("PMfugitive—Mitigating the Environmental and Health Impacts of Particles from Fugitive Emissions") and the PhD fellowship SFRH/BD/78698/2011. The FCT support is also acknowledged by C2TN/IST authors (UIDB/04349/2020+UIDP/04349/2020), by CESAM authors (UIDB/50017/2020+UIDP/50017/2020) and by CQE author (UIDB/00100/2020).

**Conflicts of Interest:** The authors declare no conflict of interest.
