Chemical composition of PM1 and PM2.5 at a suburban site in southern Italy

Abstract

Organic (OC) and elemental carbon (EC), inorganic ions (Cl⁻, NO₃⁻, SO₄²⁻, Na⁺, NH₄⁺, K⁺, Ca²⁺), methanesulfonate (MSA⁻) and metals (Al, Fe, Pb, Mn, Ba, V) were monitored in PM1 and PM2.5 samples collected at a suburban site in south-eastern Italy, to contribute to the characterisation of fine particles in the Central Mediterranean. Mean mass concentrations are 13 µg/m³ and 22 µg/m³ in PM1 and PM2.5, respectively. OC, EC, SO₄²⁻, NH₄⁺, NO₃⁻, K⁺ and Ca²⁺ are predominant components and account for 54% and 56% of the PM1 and PM2.5 mass, respectively. OC, EC, SO₄²⁻, NH₄⁺, K⁺ and Ca²⁺ concentrations lie in the range of the corresponding ones measured in PM1 and PM2.5 samples collected at suburban/urban Mediterranean sites. NO₃⁻ and trace element concentrations lie in the range of the corresponding ones measured in PM1 and PM2.5 samples collected at remote/background Mediterranean sites. The biogenic nss-SO₄²⁻ accounts for ~5% and 4% of nss-SO₄²⁻ in PM1 and PM2.5, respectively. The seasonal trend of the components partitioning and the interspecies correlation analysis in PM1 and PM2.5-1 indicated that the PM1 and PM2.5-1 components depend on season and are likely not controlled by similar sources, and/or similar generation processes, and/or similar transport patterns. The sulfur and nitrogen oxidation ratios were calculated to contribute to the understanding of the seasonal dependence of nitrate and sulfate concentrations in PM1 and PM2.5-1. The mass closure analysis showed that organic matter (OM), EC, and nitrate mass percentages are larger in autumn–winter. NH₄⁺, nss-SO₄²⁻, and crustal matter mass percentages are larger in spring–summer. Finally, the ratio of the crustal matter in PM1 to that in PM2.5-1, which is 0.2 and 0.3 in spring–summer and autumn–winter, respectively, and the higher (OM+EC) contribution in PM1 than in PM2.5-1 led to the conclusion that PM1 would be a better indicator for fine-anthropogenic particles than PM2.5.

Keywords:

• organic carbon
• elemental carbon
• ions
• metals
• MSA⁻
• mass closure analysis

Acknowledgements

The financial support by the European Community through the ACTRIS Research Infrastructure Action under the 7th Framework Programme under ACTRIS Grant Agreement n° 262254 is gratefully acknowledged. The Regional Air Agency ARPA Puglia is acknowledged for providing NO₂ and SO₂ mass concentrations. Dr S. Di Sabatino from Università del Salento is acknowledged for providing ground meteorological data.