Composition of fine and coarse particles in a coastal site of the central Mediterranean: Carbonaceous species contributions

Abstract

Total Suspended Particulate (TSP) and PM2.5 samples simultaneously collected at a coastal site (40.4°N; 18.1°E) in the central Mediterranean are analyzed to investigate the relative role of ions (Cl−, NO3−, SO42−, Na+, NH4+, K+, Mg2+, Ca2+) and carbonaceous species in the fine (PM2.5) and coarse (TSP–PM2.5) sampled mass. A methodology is described to determine carbonate carbon (CC), organic carbon (OC), and elemental carbon (EC) levels from Thermal Optical Transmittance (TOT) measurements since carbonate particles may significantly contribute to the Mediterranean particulate. We have found that CC levels vary up to 1.7 μg m−3 and 0.8 μg m−3 in the coarse and fine fraction, respectively. OC and EC levels vary up to 3.0 μg m−3 and 1.5 μg m−3, respectively in the coarse fraction, and vary within the 2.2–10 μg m−3 and 0.5–5 μg m−3 range, respectively in the fine fraction. Hence, OC levels may be overestimated mainly in the coarse fraction, if the CC contribution is not accounted for. CO32− levels (calculated from CC concentrations) account on average for 6% and 10% of the fine and coarse mass, respectively and allow balancing the anion deficit resulting from the ionic balance of ions detected by ion chromatography (IC). Total carbon TC = (OC + EC) accounts on average for 29% and 6% of the fine and coarse mass, respectively. IC ions account for 38% and 17% of the fine and coarse mass, respectively. OC, EC, SO42−, NH4+, and K+ are the major components in the fine fraction, accounting on average for 84% of the analyzed PM2.5 mass. Marine- and crust-originated ions (Cl−, Mg2+, Na+, Ca2+, CO32−) and NO3− are mainly in the coarse fraction and represent on average 83% of the analyzed coarse mass.