| 1. |
- Pasquier, J. T., et al.
(författare)
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The Ny-Ålesund Aerosol Cloud Experiment (NASCENT) : Overview and First Results
- 2022
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Ingår i: Bulletin of The American Meteorological Society - (BAMS). - 0003-0007 .- 1520-0477. ; 103:11, s. e2533-E2558
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Tidskriftsartikel (refereegranskat)abstract
- The Arctic is warming at more than twice the rate of the global average. This warming is influenced by clouds, which modulate the solar and terrestrial radiative fluxes and, thus, determine the surface energy budget. However, the interactions among clouds, aerosols, and radiative fluxes in the Arctic are still poorly understood. To address these uncertainties, the Ny-Ålesund Aerosol Cloud Experiment (NASCENT) study was conducted from September 2019 to August 2020 in Ny-Ålesund, Svalbard. The campaign’s primary goal was to elucidate the life cycle of aerosols in the Arctic and to determine how they modulate cloud properties throughout the year. In situ and remote sensing observations were taken on the ground at sea level, at a mountaintop station, and with a tethered balloon system. An overview of the meteorological and the main aerosol seasonality encountered during the NASCENT year is introduced, followed by a presentation of first scientific highlights. In particular, we present new findings on aerosol physicochemical and molecular properties. Further, the role of cloud droplet activation and ice crystal nucleation in the formation and persistence of mixed-phase clouds, and the occurrence of secondary ice processes, are discussed and compared to the representation of cloud processes within the regional Weather Research and Forecasting Model. The paper concludes with research questions that are to be addressed in upcoming NASCENT publications.
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| 2. |
- Siegel, Karolina, 1990-
(författare)
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Chemical perspectives on aerosol-cloud interactions in the High Arctic
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Atmospheric aerosol particles have important yet highly uncertain impacts on the Earth’s climate, with the largest uncertainties residing in the interactions between aerosols and clouds. The extent to which aerosols act as cloud condensation nuclei (CCN) depends on the chemical composition and size of the particles. To make correct predictions of cloud formation and the associated climate forcing, more knowledge on the physicochemical properties of aerosols is needed.This thesis investigates the chemical composition and CCN activity of aerosols in the High Arctic using a Chemical Ionization Mass Spectrometer with a Filter Inlet for Gases and Aerosols (FIGAERO-CIMS). The Arctic is the region on Earth with the current largest increase of mean surface temperature due to global warming and with big knowledge gaps in terms of aerosol-cloud-climate interactions.The first two articles focus on the region within the pack ice and marginal ice zone (MIZ) during Arctic late summer. They introduce new insights into the molecular composition of organic submicron (diameter<1 μm) aerosols and the associated hygroscopicity. The composition is shown to include a wide range of carbon and oxygen numbers, with a clear contribution from dimethyl sulfide (DMS) oxidation products. Together with observations of the inorganic aerosol fraction and CCN, the aerosol is shown to be highly hygroscopic, and the activation diameter and CCN number concentration to be possible to predict using κ-Köhler theory.The last two articles present results from a year-long study in Ny-Ålesund, Svalbard. The third article addresses the seasonality of DMS oxidation products, with a focus on the newly discovered compound hydroperoxymethyl thioformate (HPMTF). The analysis shows that gas-phase HPMTF follows the same development pattern in summer as the well-known oxidation product methylsulfonic acid (MSA), indicating a local source of DMS. HPMTF was however not found in significant amounts in the particle phase in either season. In the fourth article, the chemical composition of cloud residuals (particles remaining after drying of cloud droplets) was shown to be clearly influenced by DMS oxidation products (MSA and sulfuric acid) in summer. The importance of MSA and sulfuric acid for Arctic low-level cloud formation has previously been presumed, but not confirmed by in-situ observations.
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| 3. |
- Siegel, Karolina, 1990-, et al.
(författare)
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Using Novel Molecular-Level Chemical Composition Observations of High Arctic Organic Aerosol for Predictions of Cloud Condensation Nuclei
- 2022
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Ingår i: Environmental Science and Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 56:19, s. 13888-13899
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Tidskriftsartikel (refereegranskat)abstract
- Predictions of cloud droplet activation in the late summertime (September) central Arctic Ocean are made using κ-Kohler 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.
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