Boselli, A; Caggiano, R; Cornacchia, C; Madonna, F; Mona, L; Macchiato, M; Pappalardo, G; Trippetta, S (2012). Multi year sun-photometer measurements for aerosol characterization in a Central Mediterranean site. ATMOSPHERIC RESEARCH, 104, 98-110.
Aerosol characterization at a Mediterranean site is carried out on the base of 40-month (November 2005-March 2009) measurements of aerosol optical depth (ACID) at 440 nm and Angstrom coefficient (a) at 440/870 nm collected at the atmospheric observatory of the Istituto di Metodologie per l'Analisi Ambientale of the Italian National Research Council (CNR-IMAA). Mean values of 0.161 +/- 0.004 and 1.44 +/- 0.54 are observed for AOD and a, respectively. Both AOD and a are characterized by a wide range of values from 0.03 to 0.6 and from 0.15 to 3.14, respectively, and a day-to-day variability larger than 100% for AOD <0.18 and alpha <0.95. A seasonal behavior is found with higher AOD and lower alpha values in spring-summer. Four aerosol populations are found in the count distribution of AOD. The k-means cluster analysis allowed the identification of measurements belonging to each one of the four populations identified in the AOD distribution. Four prevailing aerosol classes are identified by using back-trajectories and model analyses: dust, continental, maritime and mixed aerosols. Dust and continental aerosol are the most common at Central Mediterranean (37.5% and 41% of the cases, respectively), with a wide variability in both AOD and alpha. Only in about 4% of the cases can aerosol be classified as maritime, and however the mixing with other aerosol is not negligible. A comparative study of cluster results and aerosol type identification reveals that the classification, based on the cluster analysis, is reliable for dust event and continental case, with a confidence level of 85% and 65% respectively. Finally, the Principal Component Analysis (PCA) applied on each cluster's PM1 and trace element daily concentration reveals an influence of dust on PM1 measurements at ground level. (C) 2011 Elsevier B.V. All rights reserved.