Non-target screening of organic aerosol tracers applied to a high-alpine firn core

Abstract

<p>Ice cores are unique natural archives that provide important information about the past evolution of the Earth’s atmosphere. Whereas the inorganic atmospheric aerosol fraction is well characterized, the organic composition is less understood. The organic aerosol burden is consistently underestimated in the current state-of-the-art models, thus highlighting major gaps in our understanding of the pathways by which organic aerosols accumulate and evolve in the atmosphere. So far, organic aerosols in ice cores have been primarily reported as either bulk (e.g., water insoluble or dissolved organic carbon) or specific parameters (e.g., biomass burning tracers).<br />To provide a more comprehensive characterization of the organic fraction, we applied a non-target screening approach optimised for determining oxidation products of volatile organic compounds to a firn core collected on the Corbassière glacier (Grand Combin, Swiss Alps), in 2020, covering the period 2008-2020. In comparison with a firn core drilled two years earlier (2018), we observe a drastic disturbance of seasonal trends for certain species, such as major ions at depths corresponding to the annual layers from 2008 to 2016, induced by meltwater percolation.</p> <p>As organic tracers are present in low concentrations in the firn core, we performed solid phase extraction. The organic tracers were analysed with high-resolution mass spectrometry based on Orbitrap technology coupled with liquid chromatography. This technique makes it possible to study a wide range of individual compounds at low concentration and to identify them with MS/MS fragmentation. We can attribute molecular formulas to detected compounds by comparing the MS/MS spectra with spectral libraries (e.g., mzCloud) or reference standards. With this approach we will present a unique record of molecular composition of organic aerosol in the Corbassière firn core.<br />Furthermore, this firn core presents a unique opportunity to examine the effect of melting on the organic tracers. We found that specific burning tracers (e.g., vanillic acid, vanillin and syringaldehyde) are less affected than other biomass tracers (e.g., pinic acid) by meltwater percolation. In general, we observe a decrease in concentration of the organic tracers in the same firn core section where we also observe a decrease in major ion concentrations.</p>

Preservation of chemical and isotopic signatures within the Weißseespitze millennial old ice cap (Eastern Alps), despite the ongoing ice loss

“…As a result of these conditions, the ice contains preserved isotopic and chemical signals observed along the ice core depth. This is not to be expected a-priori considering what was revealed for other Alpine sites, such as the nearby Ortles (Gabrielli et al, 2016), the Silvretta glacier (Pavlova et al, 2015;Steinlin et al, 2015) or the Grand Combin glacier (Huber et al, 2022), where the archives have been partially lost, and flat signals (i.e., Silvretta glacier) or depleted impurity concentrations (i.e., Grand Combin) have been recorded. Furthermore, the chemical signal in the upper meters of the ice does not show any evidence of the anthropogenic increase during the 20th century known from other ice core.…”