Analysis of organic aerosol markers and chiral compounds in an ice core from the Siberian Altai using UHPLC-HRMS

The assessment of global warming and its far-reaching influences on our planet necessitates reliable and accurate climate models. For this purpose, past atmospheric conditions like aerosol composition must be studied to understand their influence on the Earth’s climate. Ice cores are valuable climate archives that preserve organic compounds from atmospheric aerosols, which can be utilized as marker species for their respective emission sources.

Secondary organic aerosols (SOAs) are formed in the atmosphere by the oxidation of volatile organic compounds (VOCs), which can be either of anthropogenic or biogenic origin. The most common precursors of SOAs are monoterpenes, which are naturally emitted by vegetation in large amounts. Furthermore, organic compounds formed during biomass burning events contribute to the aerosol budget and allow the reconstruction of paleo-fire activity. Of great interest as a marker species is the anhydrosugar levoglucosan, which is formed during the combustion of cellulose. In addition to its combustion products, intact polymeric lignin, digested via alkaline oxidative degradation, can provide information about the type of vegetation which it originated from. A large variety of these markers were analyzed in an ice core extracted from the Belukha glacier located in the Altai region of Southern Siberia covering a time span of three centuries. A sample preparation method including multiple solid phase extractions and UHPLC-HRMS analysis was employed.

Chiral compounds have the same molecular formula and atom connectivity but act like mirror images of each other. In most environmental studies, no distinction is made between these so-called enantiomers. However, chirality can affect chemical and physical properties and thus influence particle formation reactions in the atmosphere. The enantiomeric ratio of a chiral compound can also further elucidate possible emission sources. Here we present the first chiral analysis of monoterpene oxidation products in ice cores and thus on a long-term scale. For this purpose, a multiple heartcut two-dimensional liquid chromatography method (mLC-LC) was developed that allows the simultaneous determination of the enantiomeric ratios of the monoterpene oxidation products cis-pinic acid and cis-pinonic acid in complex ice core samples. This novel method was successfully applied to Belukha ice core samples.