Characteristics of water-soluble inorganic chemical components in size-resolved airborne particulate matters - Sheffield, UK

Abstract

To characterise the water-soluble inorganic components of PM₁₀ in the urban area of Sheffield, size-resolved aerosol samples were collected using an electric low pressure impactor (ELPI) during a 13-day sampling campaign in October and November 2006. Cl⁻, NO₃⁻, SO₄²⁻, and NH₄⁺ were determined by ion chromatography, and Na⁺, K⁺, Mg²⁺, and Ca²⁺ by inductively coupled plasma-mass spectrometry. Back trajectories analyses revealed that the air masses could be classified into two main groups. In the “maritime regime”, the air masses moved mostly over the sea and just short distances (ca. 100 to 150 km) over land; in the “terrestrial regime”, the air masses had moved long distances (ca. 300 to 600 km) over land before reaching the sampling site. The chemical composition of the particles was strongly influenced by the origins of the air masses. Air mass belonging to the maritime regime brought more sea-salt species such as Na⁺, Cl⁻, and Mg²⁺. Air mass belonging to the terrestrial regime carried more K⁺ and secondary components like SO₄²⁻, NO₃⁻, and NH₄⁺. Sulfate showed bimodal distribution, peaking both in the fine mode (particle size <0.96 µm) and the coarse mode (particle size >0.96 µm). Nitrate exhibited a bimodal distribution in the terrestrial regime but only a coarse mode in maritime regime. Ammonium displayed a unimodal size distribution, peaking in the fine size range, mainly bound to sulfate and nitrate. In the maritime regime, chloride showed a unimodal distribution, peaking in the coarse size range. In the terrestrial regime, chloride appeared to be bimodal with one peak in the fine mode, reflecting the presence of chloride sources from industries, and another one in the coarse mode, mainly from sea spray. Although in general the air mass trajectories can be grouped into “maritime” and “terrestrial” regimes, the results suggest that air masses reaching Sheffield have been impacted by both maritime and terrestrial sources.