| 1. |
- Boy, M., et al.
(författare)
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Interactions between the atmosphere, cryosphere, and ecosystems at northern high latitudes
- 2019
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Ingår i: Atmospheric Chemistry and Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 19:3, s. 2015-2061
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Tidskriftsartikel (refereegranskat)abstract
- The Nordic Centre of Excellence CRAICC (Cryosphere-Atmosphere Interactions in a Changing Arctic Climate), funded by NordForsk in the years 2011-2016, is the largest joint Nordic research and innovation initiative to date, aiming to strengthen research and innovation regarding climate change issues in the Nordic region. CRAICC gathered more than 100 scientists from all Nordic countries in a virtual centre with the objectives of identifying and quantifying the major processes controlling Arctic warming and related feedback mechanisms, outlining strategies to mitigate Arctic warming, and developing Nordic Earth system modelling with a focus on short-lived climate forcers (SLCFs), including natural and anthropogenic aerosols. The outcome of CRAICC is reflected in more than 150 peer-reviewed scientific publications, most of which are in the CRAICC special issue of the journal Atmospheric Chemistry and Physics. This paper presents an overview of the main scientific topics investigated in the centre and provides the reader with a state-of-the-art comprehensive summary of what has been achieved in CRAICC with links to the particular publications for further detail. Faced with a vast amount of scientific discovery, we do not claim to completely summarize the results from CRAICC within this paper, but rather concentrate here on the main results which are related to feedback loops in climate change-cryosphere interactions that affect Arctic amplification.
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| 2. |
- Brasseur, Z., et al.
(författare)
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Measurement report: Introduction to the HyICE-2018 campaign for measurements of ice-nucleating particles and instrument inter-comparison in the Hyytiala boreal forest
- 2022
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Ingår i: Atmospheric Chemistry and Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 22:8, s. 5117-5145
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Tidskriftsartikel (refereegranskat)abstract
- The formation of ice particles in Earth's atmosphere strongly influences the dynamics and optical properties of clouds and their impacts on the climate system. Ice formation in clouds is often triggered heterogeneously by ice-nucleating particles (INPs) that represent a very low number of particles in the atmosphere. To date, many sources of INPs, such as mineral and soil dust, have been investigated and identified in the low and mid latitudes. Although less is known about the sources of ice nucleation at high latitudes, efforts have been made to identify the sources of INPs in the Arctic and boreal environments. In this study, we investigate the INP emission potential from high-latitude boreal forests in the mixed-phase cloud regime. We introduce the HyICE-2018 measurement campaign conducted in the boreal forest of Hyytiala, Finland, between February and June 2018. The campaign utilized the infrastructure of the Station for Measuring Ecosystem-Atmosphere Relations (SMEAR) II, with additional INP instruments, including the Portable Ice Nucleation Chamber I and II (PINC and PINCii), the SPectrometer for Ice Nuclei (SPIN), the Portable Ice Nucleation Experiment (PINE), the Ice Nucleation SpEctrometer of the Karlsruhe Institute of Technology (INSEKT) and the Microlitre Nucleation by Immersed Particle Instrument (mu L-NIPI), used to quantify the INP concentrations and sources in the boreal environment. In this contribution, we describe the measurement infrastructure and operating procedures during HyICE-2018, and we report results from specific time periods where INP instruments were run in parallel for inter-comparison purposes. Our results show that the suite of instruments deployed during HyICE-2018 reports consistent results and therefore lays the foundation for forthcoming results to be considered holistically. In addition, we compare measured INP concentrations to INP parameterizations, and we observe good agreement with the Tobo et al. (2013) parameterization developed from measurements conducted in a ponderosa pine forest ecosystem in Colorado, USA.
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| 3. |
- Castarède, Dimitri, et al.
(författare)
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A thermodynamic description for the hygroscopic growth of atmospheric aerosol particles
- 2018
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Ingår i: Atmospheric Chemistry and Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 18:20, s. 14939-14948
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Tidskriftsartikel (refereegranskat)abstract
- The phase state of atmospheric particulate is important to atmospheric processes, and aerosol radiative forcing remains a large uncertainty in climate predictions. That said, precise atmospheric phase behavior is difficult to quantify and observations have shown that "precondensation" of water below predicted saturation values can occur. We propose a revised approach to understanding the transition from solid soluble particles to liquid droplets, typically described as cloud condensation nucleation - a process that is traditionally captured by Kohler theory, which describes a modified equilibrium saturation vapor pressure due to (i) mixing entropy (Raoult's law) and (ii) droplet geometry (Kelvin effect). Given that observations of precondensation are not predicted by Kohler theory, we devise a more complete model that includes interfacial forces giving rise to predeliquescence, i.e., the formation of a brine layer wetting a salt particle at relative humidities well below the deliquescence point.
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| 4. |
- Castarède, Dimitri, et al.
(författare)
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Development and characterization of the Portable Ice Nucleation Chamber 2 (PINCii)
- 2023
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Ingår i: Atmospheric Measurement Techniques. - 1867-1381. ; 16:16, s. 3881-3899
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Tidskriftsartikel (refereegranskat)abstract
- The Portable Ice Nucleation Chamber 2 (PINCii) is a newly developed continuous flow diffusion chamber (CFDC) for measuring ice nucleating particles (INPs). PINCii is a vertically oriented parallel-plate CFDC that has been engineered to improve upon the limitations of previous generations of CFDCs. This work presents a detailed description of the PINCii instrument and the upgrades that make it unique compared with other operational CFDCs. The PINCii design offers several possibilities for improved INP measurements. Notably, a specific icing procedure results in low background particle counts, which demonstrates the potential for PINCii to measure INPs at low concentrations ( < 10 L (-1)). High-spatial-resolution wall-temperature mapping enables the identification of temperature inhomogeneities on the chamber walls. This feature is used to introduce and discuss a new method for analyzing CFDC data based on the most extreme lamina conditions present within the chamber, which represent conditions most likely to trigger ice nucleation. A temperature gradient can be maintained throughout the evaporation section in addition to the main chamber, which enables PINCii to be used to study droplet activation processes or to extend ice crystal growth. A series of both liquid droplet activation and ice nucleation experiments were conducted at temperature and saturation conditions that span the spectrum of PINCii's operational conditions ( 50 <= temperature <= 15 degrees C and 100 <= relative humidity with respect to ice <= 160 %) to demonstrate the instrument's capabilities. In addition, typical sources of uncertainty in CFDCs, including particle background, particle loss, and variations in aerosol lamina temperature and relative humidity, are quantified and discussed for PINCii.
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| 5. |
- Castarède, Dimitri
(författare)
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Water Condensation and Freezing in the Atmosphere: Exploring Deliquescence and Ice Nucleation
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Atmospheric aerosols play key roles in numerous atmospheric processes. They affect human health, are substrates and components for atmospheric chemistry, and via their contribution to clouds affect the water cycle and the energy balance of the planet. The role of aerosols in these processes involves large uncertainty and this partly comes from an incomplete understanding of the aerosol phase state in the atmosphere. In fact, as aerosols travel through the atmosphere they may be exposed to temperature and humidity conditions that alter their properties. Although some of the mechanisms involved such as the deliquescence of soluble particles and the nucleation of cloud droplets are reasonably well understood. Others, like hygroscopic growth below deliquescence and heterogeneous ice nucleation remain poorly understood. This thesis aims to fill some of these knowledge gaps. For clarity, the report is thematically separated between Pre-Deliquescence that has contributed to three published papers (Papers I, II and III) and Ice Nucleation. Ice Nucleation involves significant instrumentation development and has contributed to one measurement report (Paper IV) and one technical paper presenting the developed instrument (Paper V). I. Pre-Deliquescence Soluble particles are characterized by their ability to dissolve into liquid water. They take part in unique processes such as their complete solvation into brine droplets below water saturation (deliquescence); and their surface solvation into thin liquid films below deliquescence (pre-deliquescence). The transition from solid soluble particles to liquid droplets is typically captured by Köhler theory which describes a modified equilibrium vapor pressure due to (i) mixing entropy (Raoult’s law) and (ii) droplet geometry (Kelvin effect). However, this description omits the existence of a pre-deliquesced state. Therefore we develop a more complete model that accounts for interfacial forces giving rise to predeliquescence, in a manner akin to surface melting. The validity of the model is tested against previous hygroscopicity measurements of sodium chloride particles and results show that the model is able to reproduce observations using a set of physically realistic parameters. In Papers II and III the surface chemical composition of two common atmospheric salts, sodium acetate and ammonium sulfate, is observed at pre-deliquescence conditions using an ambient pressure X-ray photoelectron spectroscopy method. On the sodium acetate sample, reversible water uptake and salt dissociation is observed as humidity increases. Furthermore, a sodium depletion is observed at the sample surface after completing a deliquescence/efflorescence cycle. This is attributed to the formation of acetic acid and its enrichment at the liquid/gas interface. In the case of ammonium sulfate, species other than the salt ions are detected showing that chemistry takes place within the pre-deliquesced film. S0, HS-, HONO, and NH3(aq) appear simultaneously to salt solvation and a chemical mechanism is suggested to explain the presence of these species. II. Ice Nucleation and PINCii The ice phase represents ~ 65% of the total condensed water of clouds over the planet and is thus a key component in understanding the role of clouds on the radiative budget of the planet and on the hydrological cycle. In most tropospheric conditions (0°C ≥ T ⪆ -37°C), ice crystals result from heterogeneous nucleation processes requiring the presence of specific particles. On average, only 1 in 10^6 atmospheric particles can act as a suitable surface for ice nucleation and identifying these particles is key to understanding atmospheric ice nucleation and the development of cloud models. For this purpose, a large part of my PhD was invested in the development of a new portable ice nucleation chamber - PINCii. The details and evaluation of the PINCii instrument are presented in Paper V showing that PINCii is able to reproduce well defined activation processes such as homogeneous freezing, deliquescence and droplet formation with great accuracy. Results also show that PINCii can perform both ice nucleation and water droplet formation experiments with lower instrumental uncertainties than previous instruments of the same type. The HyICE-2018 field campaign based at the Smear II station in Hyytiälä (Finland) is presented in Paper IV. This campaign gathered various types of ice nucleation instruments in order to quantify the concentrations and identify the sources of ice nucleating particles in the boreal environment. Specific days were selected for ice nucleation instruments to run in parallel and at similar experimental conditions for inter-comparison purposes. Paper IV summarizes the aerosol properties and meteorological conditions during the campaign. It also presents the results of the inter-comparisons showing the amplitude of the deviations between the instruments present on site.
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| 6. |
- Kong, Xiangrui, et al.
(författare)
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A surface-promoted redox reaction occurs spontaneously on solvating inorganic aerosol surfaces
- 2021
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Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 374:6568, s. 747-
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Tidskriftsartikel (refereegranskat)abstract
- A surface-promoted sulfate-reducing ammonium oxidation reaction was discovered to spontaneously take place on common inorganic aerosol surfaces undergoing solvation. Several key intermediate species-including elemental sulfur (S-0), bisulfide (HS-), nitrous acid (HONO), and aqueous ammonia [NH3(aq)]-were identified as reaction components associated with the solvation process. Depth profiles of relative species abundance showed the surface propensity of key species. The species assignments and depth profile features were supported by classical and first-principles molecular dynamics calculations, and a detailed mechanism was proposed to describe the processes that led to unexpected products during salt solvation. This discovery revealed chemistry that is distinctly linked to a solvating surface and has great potential to illuminate current puzzles within heterogeneous chemistry.
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| 7. |
- Kong, Xiangrui, et al.
(författare)
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Reversibly Physisorbed and Chemisorbed Water on Carboxylic Salt Surfaces under Atmospheric Conditions
- 2020
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 124:9, s. 5263-5269
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Tidskriftsartikel (refereegranskat)abstract
- Copyright © 2020 American Chemical Society. The particle-gas interface in aerosol systems is of essential importance because it is here that many key atmospheric processes occur. In this study, we employ ambient pressure X-ray photoelectron spectroscopy (APXPS) to investigate the surface properties and processes of an atmospherically relevant carboxylic salt, sodium acetate, at subdeliquescence conditions. From the depth profiles of the elemental ratios of sodium, oxygen, and carbon, we find that after deliquescence-efflorescence cycles the salt surface is sodium-depleted. The mechanism of the observed depletion is proposed to be (i) the formation of neutral acetic acid in the solution due to the nature of the basic salt; (ii) the selective surface enhancement of neutral molecules under aqueous condition; and (iii) a hypothetical kinetic barrier to re-homogenization due to spatial separation and special local conditions on the surface, resulting in varied local surface composition. When the relative humidity gradually increases and approaches the deliquescence point, both reversible water uptake and reversible surface dissociation are confirmed by near-edge X-ray adsorption fine structure (NEXAFS) spectroscopy at the oxygen K-edge and sodium K-edge, respectively. The solvation of sodium requires a higher relative humidity than needed for water adsorption, which suggests that water molecules are taken up by the surface, but the solvation of the salt surface begins only when sufficient water molecules are present, to facilitate the process. The sodium-depleted surface requires additional adsorbed water to affect and dissolve the sodium ions in deeper regions.
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| 8. |
- Li, Jun, et al.
(författare)
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Hygroscopicity and Ice Nucleation Properties of Dust/Salt Mixtures Originating from the Source of East Asian Dust Storms
- 2022
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Ingår i: Frontiers in Environmental Science. - : Frontiers Media SA. - 2296-665X. ; 10
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Tidskriftsartikel (refereegranskat)abstract
- Dust storms are common meteorological events that occur frequently in the late spring and early summer in arid and semi-arid areas. The resulting lofted dust and salt mixtures can impact atmospheric chemistry and climate systems through the many pathways represented by aerosol-cloud-climate interactions. In this study, dust/salt samples were collected from important sources of the East Asian dust storm, including the Badain Jaran Desert, the Tengger Desert and the Ulan Buh Desert in northwestern China. Ion chromatography (IC) measurements were performed to determine the concentrations of cations and anions. The ionic concentrations, pH and dissolvable fractions of sand samples show a positive correlation, indicating that the dissolved content is rich in alkaline ions. A positive matrix factorization (PMF) receptor model was employed to analyze the IC results, and from the PMF solutions non-obvious connections to local geography emerge. The results of hygroscopic experiments of sand samples which were measured by a vapor sorption analyzer indicate that the hygroscopicity may be related to the soluble content of samples, and the observed hygroscopic behavior can be well described by a thermodynamic model. The morphology of individual particles was chemically mapped by the synchrotron-based scanning transmission X-ray microscopy, and needle-shaped CaCO3 particles were observed to adhere to more irregular high K-containing particles. Moreover, a continuous flow diffusion chamber was used to investigate the ice nucleation abilities of typical salts, with both homogeneous freezing and deposition nucleation being observed. The results indicate that the salts primarily act as cloud condensation nuclei but can also act as ice nucleating particles at low temperatures.
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| 9. |
- Schneider, J., et al.
(författare)
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The seasonal cycle of ice-nucleating particles linked to the abundance of biogenic aerosol in boreal forests
- 2021
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Ingår i: Atmospheric Chemistry and Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 21:5, s. 3899-3918
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Tidskriftsartikel (refereegranskat)abstract
- Ice-nucleating particles (INPs) trigger the formation of cloud ice crystals in the atmosphere. Therefore, they strongly influence cloud microphysical and optical properties and precipitation and the life cycle of clouds. Improving weather forecasting and climate projection requires an appropriate formulation of atmospheric INP concentrations. This remains challenging as the global INP distribution and variability depend on a variety of aerosol types and sources, and neither their short-term variability nor their long-term seasonal cycles are well covered by continuous measurements. Here, we provide the first year-long set of observations with a pronounced INP seasonal cycle in a boreal forest environment. Besides the observed seasonal cycle in INP concentrations with a minimum in wintertime and maxima in early and late summer, we also provide indications for a seasonal variation in the prevalent INP type. We show that the seasonal dependency of INP concentrations and prevalent INP types is most likely driven by the abundance of biogenic aerosol. As current parameterizations do not reproduce this variability, we suggest a new mechanistic description for boreal forest environments which considers the seasonal variation in INP concentrations. For this, we use the ambient air temperature measured close to the ground at 4.2 m height as a proxy for the season, which appears to affect the source strength of biogenic emissions and, thus, the INP abundance over the boreal forest. Furthermore, we provide new INP parameterizations based on the Ice Nucleation Active Surface Site (INAS) approach, which specifically describes the ice nucleation activity of boreal aerosols particles prevalent in different seasons. Our results characterize the boreal forest as an important but variable INP source and provide new perspectives to describe these new findings in atmospheric models.
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