Carbonaceous PM10 and PM2.5 and secondary organic aerosol in a coastal rural site near Brindisi (Southern Italy)

Abstract

Organic and elemental carbon were measured both in daily PM10 and PM2.5 and in 6 h range time PM2.5 samples collected from September 2015 to October 2015 in a coastal rural site near Brindisi in the Apulia region (Italy), in order to determine factors affecting the carbonaceous aerosol variations. Carbon content (total carbon TC) represented a considerable fraction for both PM10 and PM2.5. In particular, in PM10 samples, organic carbon (OC) varied from 1.06 to 18.32 μg m⁻³ with a mean concentration of 5 ± 4 μg m⁻³ and EC varied from 0.11 to 0.88 μg m⁻³ with a mean value of 0.41 ± 0.19 μg m⁻³. In PM2.5 samples, OC varied from 0.54 to 12.91 μg m⁻³ with a mean concentration of 3.5 ± 2.8 μg m⁻³ and EC varied from 0.11 to 0.85 μg m⁻³ with a mean value of 0.35 ± 0.18 μg m⁻³. The highest values for both parameters were recorded when the air masses were coming from NE Europe and when Saharan Dust events were recognized. The results show that OC and EC exhibited higher concentrations during the night hours, suggesting that stable atmosphere and lower mixing conditions play important roles for the accumulation of air pollutants and promote condensation or adsorption of semivolatile organic compounds. In samples from a Saharan Dust event and in samples with the lowest and the highest OC_sec, ATR-FTIR analysis allowed us to identify organic functional groups including the non-acid organic hydroxyl C–OH group (e.g., sugars, anhydrosugars, and polyols), carbonyl C=O group, carboxylic acid COOH group, aromatic and aliphatic unsaturated C=C–H group, aliphatic saturated C–C–H group, and amine NH₂ group. Some inorganic ions were also identified: carbonates, sulfate, silicate, and ammonium. The dusty samples are mainly characterized by the presence of carbonate and hydrogen sulfate ions and by kaolinite (absorption at 914 and 1010 cm⁻¹), while in samples with air masses coming from the NE, OC is mainly characterized by aliphatic and aromatic C–H and O–H and N–H groups (absorptions in the range 3500–2700 cm⁻¹) and by the presence of organonitrate, aromatic amide and amine, and carboxylic acids (absorptions at 1630 and 1770–1700 cm⁻¹).

Graphical abstract

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