Speciation Of Magnesium In Aerosols Using X-Ray Absorption Near-Edge Structure Related To Its Contribution To Neutralization Reactions In The Atmosphere

Aerosols, including mineral dust, are transported from China and Mongolia to Japan, particularly in spring. It has been recognized that calcium (Ca) carbonate is the main Ca species in aerosols, which reacts with acidic species such as sulfuric and nitric acids at the surface of mineral dust during its long-range transport, related to mitigation of acid depositions. The similar assumption that magnesium (Mg) originally takes the form of carbonate and contributes to the neutralization reaction and buffering effect on the acidity of aerosols has been suggested in various studies. However, few studies have confirmed this process by measuring actual Mg species in aerosols quantitatively. In this study, X-ray absorption near-edge structure (XANES) spectroscopy was employed to determine Mg species in size-fractionated aerosol samples, including mineral dust. The results showed that (i) most Mg in the mineral dust did not take the form of carbonate and its reacted species (e.g., sulfate and nitrate) produced by the neutralization reaction, but (ii) Mg was mainly found as Mg in the octahedral layer in phyllosilicates. Given that the reactivity of such Mg in phyllosilicates is much lower than those in carbonate minerals, the contribution of Mg to the neutralization reactions in the atmosphere must be lower than previously expected.