Using Novel Molecular-Level Chemical Composition Observations of High Arctic Organic Aerosol for Predictions of Cloud Condensation Nuclei

Abstract

Predictions of cloud droplet activation in the late summertime (September) central Arctic Ocean are made using κ -Köhler theory with novel observations of the aerosol chemical composition from a high-resolution time-of-flight chemical ionization mass spectrometer with a filter inlet for gases and aerosols (FIGAERO-CIMS) and an aerosol mass spectrometer (AMS), deployed during the Arctic Ocean 2018 expedition onboard the Swedish icebreaker Oden . We find that the hygroscopicity parameter κ of the total aerosol is 0.39 ± 0.19 (mean ± std). The predicted activation diameter of ∼25 to 130 nm particles is overestimated by 5%, leading to an underestimation of the cloud condensation nuclei (CCN) number concentration by 4–8%. From this, we conclude that the aerosol in the High Arctic late summer is acidic and therefore highly cloud active, with a substantial CCN contribution from Aitken mode particles. Variability in the predicted activation diameter is addressed mainly as a result of uncertainties in the aerosol size distribution measurements. The organic κ was on average 0.13, close to the commonly assumed κ of 0.1, and therefore did not significantly influence the predictions. These conclusions are supported by laboratory experiments of the activation potential of seven organic compounds selected as representative of the measured aerosol.

Highly Hygroscopic Aerosols Facilitate Summer and Early‐Autumn Cloud Formation at Extremely Low Concentrations Over the Central Arctic Ocean

“…Using data from the last 9 days of our expedition (September 11‐19), Siegel et al. (2022) conducted an aerosol‐CCN closure study and observed good general agreement between predicted and observed CCN concentrations based on chemical analysis and aerosol size distribution, with overall uncertainties below 20%. However, they also inferred high κ values for the Aitken mode which could not be explained with the chemical analysis.…”

“…However, not only did sodium concentration not increase around freeze-up, but also TEM image analyses from the Arctic Summer Cloud Ocean Study in 2008 in the same region and season has shown that sodium is organically bonded (Hamacher-Barth et al, 2016), which would potentially limit its hygroscopicity. Using data from the last 9 days of our expedition (September 11-19), Siegel et al (2022) conducted an aerosol-CCN closure study and observed good general agreement between predicted and observed CCN concentrations based on chemical analysis and aerosol size distribution, with overall uncertainties below 20%. However, they also inferred high κ values for the Aitken mode which could not be explained with the chemical analysis.…”

“…The hygroscopicity parameter κ is compound‐ and mixture‐specific and ranges from 0 for insoluble compounds such as soot (Weingartner et al., 1997) to 1.5 for very hygrophilic compounds such as pure sodium chloride (Zieger et al., 2017). While the hygroscopicity of single compounds and simple mixtures, such as sodium chloride and sulfuric acid, have been well explored (Schmale et al., 2018; Siegel et al., 2022; Svenningsson et al., 2006; Zieger et al., 2017), knowledge of ambient Arctic aerosol hygroscopicity still suffers from a deficit in measurements and modeling gaps (Schmale et al., 2021), since the aerosol sources, and therefore composition and size, are still poorly characterized.…”

Large-eddy simulation of a two-layer boundary-layer cloud system from the Arctic Ocean 2018 expedition

“…A custom-built differential mobility particle sizer (DMPS) with a sample flow 0.36 dm 3 min -1 was used to measure the aerosol particle number size distribution in the size range 10 to 921 nm at a time resolution of 9 minutes. More technical details can be found in Karlsson et al (2022) and the data can be accessed through Karlsson and Zieger (2020). The DMPS combined a Vienna-type differential mobility analyzer (inner/outer r= 25/33.5 mm and a length of 280 mm) with a mixing condensation particle counter (MCPC; Model 1720 from 155 Brechtel Manufacturing Inc., USA).…”

Glucose Enhances Salinity-Driven Sea Spray Aerosol Production in Eastern Arctic Waters

“…Other investigations highlighted additional key factors for SSA production, such as sea surface temperature, upper ocean turbulence, seawater density, and concentration of organics. These factors affect the seawater surface tension, rise time of bubbles, and the bubble-bursting processes, and consequently, also affect sea spray ejection. ,− Park et al, for instance, provided evidence that SSA production is enhanced by riverine organics. The AO surface waters harbor microorganisms and a myriad of active organic compounds such as proteins, carbohydrates (saccharides), fatty acids, amino acids, exopolymers, and cellular debris. ,− Most of these compounds are planktonic food web byproducts and small molecular weight metabolites that are released as phytoplankton exudates .…”