PM2.5 and PM10 in the urban area of Naples: chemical composition, chemical properties and influence of air masses origin

Abstract

In order to investigate particulate matter characteristics in the urban area of Naples, South of Italy, PM₁₀ and PM_2.5 chemical composition and properties were determined; in particular, ionic composition (Na⁺, K⁺, NH₄⁺, Mg²⁺, Ca²⁺, HCOO-, CH₃COO^?, Cl^?, NO₂^?, NO₃^?, SO₄^2?, C₂O₄^2?) and concentration of specific metals (Pb, Cd, Cu and Zn) were evaluated in association with an air masses trajectories study. Information on major ions was used to conduct the ionic balance and to evaluate sea salt and non-sea salt contributions; furthermore, the study on metals concentration allowed to distinguish the contribution of anthropic sources while their chemical behaviour (solubility and leachability) was considered in order to highlight the presence of different chemical forms. In the period of interest (June 2015), daily averages PM concentrations were below the limit of 25?μg/m³ for PM_2.5 and 50?μg/m³for PM₁₀; moreover, for both fractions, the most abundant ionic species was SO₄^2?followed by NO₃^?. Ionic balance indicated that non-sea salt contribution accounted for the great part of Ca²⁺, SO₄^2? and K⁺ while secondary inorganic aerosol accounted for about 5% of total ionic fraction. As expected, the most abundant metal was zinc (about 41?ng/m³ and 44?ng/m³in PM_2.5 and PM_10, respectively), while cadmium, copper and lead were at very low concentrations, in the range of 0.01–0.47?ng/m³; leachability reached values of 40% for copper in both PM fractions, in contrast with zinc that showed the lowest leachability, corresponding to 6% for PM_2.5 fraction. The study on air masses trajectories indicated a change on ionic composition and chemical properties, varying from a condition with air masses coming from Eastern Europe, characterised also by higher concentrations of both PM_2.5 and PM₁₀, a prevalence of secondary aerosol and metals showing minor solubility and leachability, to a condition with air masses coming from North-west region, with characteristics opposed to the previous ones.