Secondary Organic Aerosol formed from VOCs Emitted by Arctic Macroalgae and their Cloud-Forming potential

The Arctic region is a key component of the climate system on Earth and has been observed to warm at a rate exceeding the rest of the globe. Knowledge on atmosphere-biosphere interactions in Arctic ecosystems is missing to understand this trend. This work targets the volatile organic compounds (VOCs) emitted in the Arctic region, their potential to form aerosols, and the ability of these particles to act as nuclei for clouds.

            Brown macroalgae are important species in Arctic marine ecosystems. They have been shown to be a source of atmospheric VOCs, in the form of halocarbons (CHBr₃, CH₂Br₂, CH₂I₂…), species, and non-halogenated compounds. In addition, they also release iodine (I₂). It is however challenging to characterize the full emission spectrum from macroalgae under different conditions, i.e., low tide, high tide, dark and daytime; key information is still missing and further input is necessary. The most reactive compounds i.e., I₂ have been shown to participate in SOA formation in the presence of light and ozone (O₃). However, very few studies investigate the co-emitted VOC to I₂-catalyzed SOA formation and knowledge on these contributions are missing.

            To address this, we have investigated VOC emissions from Ascophyllum nodosum, a common brown macroalgae (collected in Southwest Greenland), and mimicked atmospheric oxidation and SOA formation in the presence of light and ozone using the Aarhus University Research on Aerosol (AURA) simulation chamber. The clouds forming ability of the generated SOA were measured, and the hygroscopicity parameter κ (kappa), which is widely used to describe the water uptake processes in climate models, was determined. Measurements of “κ” and interpretations thereof are supported with online and offline mass spectrometry measurements to determine the chemical composition of both gas and aerosol phases.

Overall, this study provides an estimate of the SOA formation from the entire spectrum of VOCs emitted by living macroalgae under sunlight/dark and low tide conditions. In combination with the detailed assessment of their potential to form clouds we will discuss how our results contribute to an improved understanding of Arctic climate.

This work was supported by the Novo Nordisk Foundation, the Danish National Research Foundation (DNRF17), the Carlsberg Foundation and ACTRIS-DK.