Aerosol silicon and associated elements in the arctic high and mid-troposphere

Abstract

In six aircraft flights of AGASP-II, 2–15 April 1986, from ca. 1300–8100 m altitude, the most abundant elements measured in size separated aerosol samples were silicon, chlorine, and sulfur. Concentrations were higher than at ground level (G), particularly at highest altitudes (HT, 5600–8100 m, upper troposphere to lower stratosphere) compared to mid troposphere (MT, 1300–4700 m), especially for ultrafine particles <0.0625 μm aerodynamic diameter. HT and MT median and G average concentrations, μm⁻³ STP, respectively (1) Si = 3.64, 1.30, 0.092; (2) S = 1.44, 0.265, 0.087; (3) Cl = 1.62, 0.36, 0.213. The weight ratio Al/Si was less than half that expected for Earth crust material (0.3), evidence against fine silicon originating mainly by dispersion of volcanic debris or other eolian dust particles. Instead, pollution from high rank (mainly bituminous) coal combustion, which can form SiO vapors from quartz in the ash and fine alkaline aerosol with low Al/Si ratio, is a more likely source of apparently widespread aerosol silicon contamination of the Arctic atmosphere. Chlorine and sulfur gases may be scavenged by coarse alkaline dust particles and acidic chlorine and sulfur may be derived from coal combustion processes, thus also accounting for their high concentrations.