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Dimethyl sulfide (DMS) influences climate via cloud condensation nuclei (CCN) formation resulting from its oxidation products (mainly methanesulfonic acid, MSA, and sulfuric acid, H2SO4). Despite their importance, accurate prediction of MSA and H2SO4from DMS oxidation remains challenging. With comprehensive experiments carried out in the Cosmics Leaving Outdoor Droplets (CLOUD) chamber at CERN, we show that decreasing the temperature from +25 to -10 °C enhances the gas-phase MSA production by an order of magnitude from OH-initiated DMS oxidation, while H2SO4production is modestly affected. This leads to a gas-phase H2SO4-to-MSA ratio (H2SO4/MSA) smaller than one at low temperatures, consistent with field observations in polar regions. With an updated DMS oxidation mechanism, we find that methanesulfinic acid, CH3S(O)OH, MSIA, forms large amounts of MSA. Overall, our results reveal that MSA yields are a factor of 2-10 higher than those predicted by the widely used Master Chemical Mechanism (MCMv3.3.1), and the NOxeffect is less significant than that of temperature. Our updated mechanism explains the high MSA production rates observed in field observations, especially at low temperatures, thus, substantiating the greater importance of MSA in the natural sulfur cycle and natural CCN formation. Our mechanism will improve the interpretation of present-day and historical gas-phase H2SO4/MSA measurements. publishedVersion

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., Atmospheric Chemistry and Physics, 22 (8), ISSN:1680-7375, ISSN:1680-7367

Satellite- and aircraft-based mid-infrared measurements of polar stratospheric clouds (PSCs) have provided spectroscopic evidence for the presence of β-NAT (nitric acid trihydrate) particles. Metastable nitric acid hydrate phases such as α-NAT and α-NAD (nitric acid dihydrate) have been frequently observed in laboratory experiments, but not yet detected as a constituent of PSCs in atmospheric measurements. As for the β-NAD modification, its formation was first observed in X-ray diffraction measurements when the low-temperature α-NAD phase was warmed to a temperature above 210 K. Its infrared spectrum has been reported, but so far no optical constants have been derived that could be used as input for infrared retrievals of PSC composition. In this work, we show that β-NAD particles were efficiently formed in isothermal, heterogeneous crystallisation experiments at 190 K from supercooled HNO3/H2O solution droplets containing an embedded mineral dust or meteoric smoke particle analogue. An inversion algorithm based on a T-matrix optical model was used to derive for the first time the mid-infrared complex refractive indices of the β-NAD modification from the measured extinction spectrum of the particles. In contrast to the heterogeneous crystallisation experiments, the α-NAD phase was formed when the HNO3/H2O solution droplets did not contain a solid nucleus and crystallised homogeneously. Using a light scattering detector that recorded two-dimensional scattering patterns of the crystallised NAD particles, we were able to determine predominant shapes of the α- and β-NAD crystals. We found that α-NAD grew into elongated, needle-shaped crystals, while β-NAD particles were compact in shape. This agrees with previously reported images of α- and β-NAD particles grown on the cryo-stage of an Environmental Scanning Electron Microscope.

Earlier chapters of this work have described procedures and protocols that are applicable to most chambers, this chapter has a slightly different focus; we predominantly consider multiphase processes where the applications are on phase transfer of chemical species rather than chemical reactions and the processes are generally occurring in highly specialized chambers. Three areas are described. Firstly, cloud formation processes; here, precise control of physical and thermodynamic properties is required to generate reproducible results. The second area examined is the air/sea interface, looking at the formation of aerosols from nonanoic acid as a surfactant with humic acid as a photosensitizer. The final apparatus described is the Roland von Glasow sea-ice chamber where a detailed protocol for the reproducible formation of sea-ice is given along with an outlook of future work. The systems studied in all three sections are characterized by difficulties in making detailed in situ observations in the real world, either due to the transitory nature of systems or the practical difficulties in accessing the systems. While these specialized simulation chambers may not perfectly reproduce conditions in the real world, the chambers do provide more facile opportunities for making extended and reproducible measurements to investigate fundamental physical and chemical processes, at significantly lower costs.

Atmospheric simulation chambers are often utilized to study the physical properties and chemical reactivity of particles suspended in air. In this chapter, the various approaches employed for the addition of particles to simulation chambers are described in detail. Procedures for the generation of monodispersed seed aerosols, mineral dust, soot particles and bioaerosols are all presented using illustrative examples from chamber experiments. Technical descriptions of the methods used for the addition of whole emissions (gases and particles) from real-world sources such as wood-burning stoves, automobile engines and plants are also included, along with an outline of experimental approaches for investigating the atmospheric processing of these emissions.

Ice growth from vapor deposition is an important process for the evolution of cirrus clouds, but the physics of depositional ice growth at the low temperatures ( K) characteristic of the upper troposphere and lower stratosphere is not well understood. Surface attachment kinetics, generally parameterized as a deposition coefficient αD, control ice crystal habit and also may limit growth rates in certain cases, but significant discrepancies between experimental measurements have not been satisfactorily explained. Experiments on single ice crystals have previously indicated the deposition coefficient is a function of temperature and supersaturation, consistent with growth mechanisms controlled by the crystal's surface characteristics. Here we use observations from cloud chamber experiments in the Aerosol Interactions and Dynamics in the Atmosphere (AIDA) aerosol and cloud chamber to evaluate surface kinetic models in realistic cirrus conditions. These experiments have rapidly changing temperature, pressure, and ice supersaturation such that depositional ice growth may evolve from diffusion limited to surface kinetics limited over the course of a single experiment. In Part 1, we describe the adaptation of a Lagrangian parcel model with the Diffusion Surface Kinetics Ice Crystal Evolution (DiSKICE) model (Zhang and Harrington, 2014) to the AIDA chamber experiments. We compare the observed ice water content and saturation ratios to that derived under varying assumptions for ice surface growth mechanisms for experiments simulating ice clouds between 180 and 235 K and pressures between 150 and 300 hPa. We found that both heterogeneous and homogeneous nucleation experiments at higher temperatures (>205 K) could generally be modeled consistently with either a constant deposition coefficient or the DiSKICE model assuming growth on isometric crystals via abundant surface dislocations. Lower-temperature experiments showed more significant deviations from any depositional growth model, with different ice growth rates for heterogeneous and homogeneous nucleation experiments.

The presence of ice in mixed-phase clouds has a vital impact on their radiative properties, lifetime, and ability to precipitate. Ice crystal formation is initially induced by a rare subset of ambient aerosol particles called ice-nucleating particles (INPs). Despite the importance of INPs on aerosol-cloud interactions and century-long research efforts, the knowledge about their nature and atmospheric abundance still needs improvement. Recent instrument developments allow more automated and continuous INP measurements with a high time resolution, to gain a better understanding of the natural variability of INPs in different locations, and to investigate the identity and source regions of them. Here we present long-term observations of INPs at Storm Peak Laboratory (SPL) located in the Rocky Mountains of Colorado. SPL is at an altitude of 3200 m a.s.l. within the lower free troposphere, and in winter it is a location where mixed-phase clouds frequently occur. Therefore, the present aerosol particles are directly relevant for ice formation in such clouds. The ongoing INP measurements started in October 2021, and are conducted with the Portable Ice Nucleation Experiment (PINE) at conditions resembling the formation of mixed-phase clouds at temperatures between -22°C and -32°C. Results on the short-term and inter-seasonal variability will be presented, with a focus on parallel measurements of aerosol particle properties and meteorology. During the winter months of January and February 2022, we characterized the size of the INPs by selecting ice crystal residuals downstream of PINE using a pumped-counterflow virtual impactor and a novel optical particle counter. As this setup operates continuously, it is capable to investigate INP properties for longer time periods and to improve sampling statistics. In the future, it will be used with other diagnostic instruments, such as a single particle mass spectrometer, giving insights into the size and chemical composition of INPs, and thus allows to have a direct measure of the nature of INPs in ambient air.

Although the coverage of ice-nucleating particle (INP) measurements grows more comprehensively distributed by the year, studies measuring comprehensive aerosol properties often focus extensively on one or two sites at most, and methodology between studies even within the same lab is rarely the same as methods are refined and study aims differ. This inconsistency in part contributes to a sizeable uncertainty in effective radiative forcing estimation in regard to aerosol cloud interactions. To complement our insufficient knowledge of aerosol properties, we compiled and assessed a multitude of aerosol measurements from four sites: Graciosa Island to represent a predominantly marine site (data from autumn 2020), central Oklahoma to represent a mid-latitude terrestrial site (data from autumn 2019), and Utqiagvik, Alaska (data from autumn 2021) and Ny-Ålesund, Svalbard (data from autumn 2019 and 2020) to represent Arctic sites in different longitudes.Here we report both total aerosol concentration as well as information related to two distinct aerosol concentrations: INPs and cloud concentration nuclei (CCN). INPs were measured using a single online and two offline methods, while CCN and total aerosol concentrations were measured with the same methods and similar instrumentation. This dataset can allow a broad-level comparison of several contrasting sites which would be expected to have vastly different INP and CCN activated fractions and total concentrations due to the variety in aerosol sources around the globe. Our spatial variation analysis indicates the aerosol concentrations vary by up to two orders of magnitude between sites (approximately 101 to 103 particles per cubic centimeter), while INP and CCN concentrations measured by two comparable methods vary by an order of magnitude (approximately 101 to 102 INPs per liter, and approximately 101 to 102 CCN per cubic centimeter) and INPs show much less variation than the ranges reported by previous studies. This small range may be due to similarities in INP composition, even as total aerosol population composition varies. For instance, INPs at all sites include a population of dust aerosols (either locally sourced or long-range transported). On the other hand, the total aerosol sources are more divergent between sites, especially between continental and marine-dominant sites where the greatest differentiation is seen. As well, previous studies have focused on a yearly average rather than a single season, which may also lead to greater variation. There is also variation in the heat-sensitivity of the INP samples, with continental samples from Graciosa Island showing the least heat sensitivity. Carefully comparing a large dataset containing a variety of aerosol property information including INP and CCN concentrations will allow us to determine patterns in the global distribution of aerosols that will be important as future climate models are developed.

Cirrus are high-level clouds composed uniquely of ice crystals. To correctly estimate their radiative contribution to the Earth’s energy budget, it is necessary to know their optical properties, which in turn depend on the formation mechanism. Cirrus clouds can form either by homogeneous freezing of supercooled aqueous solution droplets or by heterogeneous freezing with the contribution of an ice nucleating particle (INP). Therefore, it is fundamental to understand which aerosol particles are present in the upper troposphere and contribute to initiate heterogeneous ice nucleation.Sulphate particles are among the most abundant aerosol types in the upper troposphere, and their degree of neutralization with ammonia significantly varies with geographical location and altitude. According to the ammonium-to-sulphate ratio (ASR), three pure inorganic salts can form in the H2SO4/NH3/H2O system: ammonium bisulphate (NH4HSO4, ASR = 1), letovicite (NH4)3H(SO4)2, ASR = 1.5), and ammonium sulphate ((NH4)2SO4, ASR = 2). However, the transport, ageing and processing of atmospheric aerosols are more likely to lead to a variety of mixtures of the different salts than to particles with exact stoichiometry. The ice nucleation ability of aqueous sulphuric acid (ASR=0) and fully neutralized crystalline ammonium sulphate particles has been extensively investigated in the past. The low-temperature phase state and ice nucleation ability of partially neutralized particles, instead, has never been measured before.In this contribution, we present new AIDA cloud chamber experiments on the crystallization, deliquescence, and ice nucleation ability of partially neutralized particles in the H2SO4/NH3/H2O system (1Our results show that in the cirrus cloud temperature range, the phase state and ice nucleation ability of particles in the H2SO4/NH3/H2O system depend on their degree of neutralization. In particular, we measured an increased ice nucleation ability with increasing degree of neutralization. Quantifying the abundance and neutralization degree of ammoniated sulphate particles in the upper troposphere may thus be critical to correctly represent their direct and indirect effect on climate.

In mixed-phase clouds, primary ice formation occurs only in the presence of ice-nucleating particles (INPs) [Vali et al., 2015], which are a very rare subset of the aerosols in the atmosphere. INPs are an important part of the earth climate system, as they can initiate the formation of precipitation [Mülmenstädt et al., 2015] and have an influence on the cloud radiative properties [Murray et. al, 2021]. In the last decades, different INP measurements have been performed within the atmospheric boundary layer at mixed-phase clouds conditions [Kanji et. al, 2017]. INP measurements in the free troposphere are challenging, as they can only be conducted by aircraft-based measurements or at high altitude mountain stations. However, it is important to study long-term INP concentrations at different altitudes and geographical locations to get a better understanding of the presence of INPs in the atmosphere.The Sonnblick Observatory (SBO) in the Austrian Alps is located at an altitude of 3106 m above sea level and is an ideal location to investigate the INP concentration in the free troposphere, as the measured INPs are directly relevant for ice formation. Since August 2019, we continuously measure the INP concentration at the SBO via filter collection and offline analysis with INSEKT (Ice Nucleation Spectrometer of the Karlsruhe Institute of Technology) [Schneider et. al, 2020]. The analysis of the sampled aerosols gives us the temperature dependent number concentration of INPs at temperatures above -25°C with a time resolution of one week. In order to receive a better insight into short-term fluctuations, we performed additional measurements with the online INP measurement PINE (Portable Ice Nucleation Experiment) [Möhler et al., 2021], since the end of July 2021. PINE has a time resolution of 5 – 6 min and usually measures at a constant temperature of ~ -23°C. In addition, INP activity screenings in the range from -15°C to -30°C are performed in regular intervals and during interesting meteorological periods such as Saharan dust events. The overlap in temperature ranges of INSEKT and PINE enables a comparison between the two measuring instruments.Our results show that there are significant seasonal variations in the INP concentration. Especially during the summer time, strong diurnal variations in the INP concentration were observed, which could be explained by the influence of convectively lifted air from the boundary layer during the day. Correlations of the measured INP concentrations to meteorological parameters, aerosol properties and boundary layer stability will be discussed. In addition, we will present a case study of a dust event, which shows a sudden, strong increase in the INP concentration.

Dust particles from high latitudes have a potentially large local, regional, and global significance to climate and the environment as short-lived climate forcers, air pollutants, and nutrient sources. Identifying the locations of local dust sources and their emission, transport, and deposition processes is important for understanding the multiple impacts of high-latitude dust (HLD) on the Earth's systems. Here, we identify, describe, and quantify the source intensity (SI) values, which show the potential of soil surfaces for dust emission scaled to values 0 to 1 concerning globally best productive sources, using the Global Sand and Dust Storms Source Base Map (G-SDS-SBM). This includes 64 HLD sources in our collection for the northern (Alaska, Canada, Denmark, Greenland, Iceland, Svalbard, Sweden, and Russia) and southern (Antarctica and Patagonia) high latitudes. Activity from most of these HLD sources shows seasonal character. It is estimated that high-latitude land areas with higher (SI ≥0.5), very high (SI ≥0.7), and the highest potential (SI ≥0.9) for dust emission cover >1 670 000 km2, >560 000 km2, and >240 000 km2, respectively. In the Arctic HLD region (≥60∘ N), land area with SI ≥0.5 is 5.5 % (1 035 059 km2), area with SI ≥0.7 is 2.3 % (440 804 km2), and area with SI ≥0.9 is 1.1 % (208 701 km2). Minimum SI values in the northern HLD region are about 3 orders of magnitude smaller, indicating that the dust sources of this region greatly depend on weather conditions. Our spatial dust source distribution analysis modeling results showed evidence supporting a northern HLD belt, defined as the area north of 50∘ N, with a “transitional HLD-source area” extending at latitudes 50–58∘ N in Eurasia and 50–55∘ N in Canada and a “cold HLD-source area” including areas north of 60∘ N in Eurasia and north of 58∘ N in Canada, with currently “no dust source” area between the HLD and low-latitude dust (LLD) dust belt, except for British Columbia. Using the global atmospheric transport model SILAM, we estimated that 1.0 % of the global dust emission originated from the high-latitude regions. About 57 % of the dust deposition in snow- and ice-covered Arctic regions was from HLD sources. In the southern HLD region, soil surface conditions are favorable for dust emission during the whole year. Climate change can cause a decrease in the duration of snow cover, retreat of glaciers, and an increase in drought, heatwave intensity, and frequency, leading to the increasing frequency of topsoil conditions favorable for dust emission, which increases the probability of dust storms. Our study provides a step forward to improve the representation of HLD in models and to monitor, quantify, and assess the environmental and climate significance of HLD.

Dust particles emitted from high latitudes (≥ 50° N and ≥ 40° S, including Arctic as a subregion ≥ 60° N), have a potentially large local, regional, and global significance to climate and environment as short-lived climate forcers, air pollutants and nutrient sources. To understand the multiple impacts of the High Latitude Dust (HLD) on the Earth systems, it is foremost to identify the geographic locations and characteristics of local dust sources. Here, we identify, describe, and quantify the Source Intensity (SI) values using the Global Sand and Dust Storms Source Base Map (G-SDS-SBM), for sixty-four HLD sources included in our collection in the Northern (Alaska, Canada, Denmark, Greenland, Iceland, Svalbard, Sweden, and Russia) and Southern (Antarctica and Patagonia) high latitudes. Activity from most of these HLD dust sources show seasonal character. The environmental and climatic effects of dust on clouds and climatic feedbacks, atmospheric chemistry, marine environment, and cryosphere-atmosphere feedbacks at high latitudes are discussed, and regional-scale modelling of dust atmospheric transport from potential Arctic dust sources is demonstrated. It is estimated that high latitude land area with higher (SI ≥ 0.5), very high (SI ≥ 0.7) and the highest potential (SI ≥ 0.9) for dust emission cover >1 670 000 km2, >560 000 km2, and >240 000 km2, respectively. In the Arctic HLD region, land area with SI ≥ 0.5 is 5.5 % (1 035 059 km2), area with SI ≥ 0.7 is 2.3 % (440 804 km2), and with SI ≥ 0.9 it is 1.1 % (208 701 km2). Minimum SI values in the north HLD region are about three orders of magnitude smaller, indicating that the dust sources of this region are highly dependable on weather conditions. In the south HLD region, soil surface conditions are favourable for dust emission during the whole year. Climate change can cause decrease of snow cover duration, retrieval of glaciers, permafrost thaw, and increase of drought and heat waves intensity and frequency, which all lead to the increasing frequency of topsoil conditions favourable for dust emission and thereby increasing probability for dust storms. Our study provides a step forward to improve the representation of HLD in models and to monitor, quantify and assess the environmental and climate significance of HLD in the future.

Swabian MOSES 2021 ist eine hydro-meteorologische Messkampagne, die zwischen Mai und Oktober 2021 im Neckartal und auf der Schwäbischen Alb im Südwesten Deutschlands im Verbund von zehn deutschen wissenschaftlichen Einrichtungen und unter Beteiligung von über 30 Forschenden durchgeführt wurde. Im Fokus von Swabian MOSES 2021 stehen zwei Wetterextreme, die nicht nur für das Untersuchungsgebiet von großer Relevanz sind: Starkniederschläge durch hochreichende Konvektion (Gewitter) und Hitzewellen mit den damit verbundenen Trockenperioden. Mehrere heftige Unwetterereignisse, aber auch sogenannte "non cases", bei denen trotz guter prä-konvektiver Bedingungen keine Gewitter entstanden, lieferten einen umfangreichen Datensatz. Mit diesem lässt sich die gesamte Ereigniskette abbilden: von der Entstehung hochreichender Konvektion über die Intensivierung und den Zerfall der Gewittersysteme, die Dynamik der damit verbundenen Begleiterscheinungen (z.B. Starkregen, Hagel, Windböen) bis hin zu Abflüssen und Schadstoffeinträgen in Fließgewässern sowie zum Wasserdampftransport in die untere Stratosphäre. Eine Hitzewelle mit Dürreepisoden hat sich dagegen nicht eingestellt. Swabian MOSES 2021 ist Teil der Implementierungsphase von MOSES (Modular Observation Solutions for Earth Systems), einem Beobachtungssystem, das vom Forschungsbereich "Erde und Umwelt" der Helmholtz-Gemeinschaft entwickelt wird. Die Koordination von MOSES liegt beim Zentrum für Umweltforschung (UFZ) in Leipzig. Federführendes Institut bei Swabian MOSES 2021 ist das Institut für Meteorologie und Klimaforschung (IMK-TRO) des Karlsruher Instituts für Technologie (KIT), welches sein mobiles integriertes Atmosphärenbeobachtungssystem KITcube als größte Messinfrastruktur einbrachte. Insgesamt wurden an über 20 Standorten im Untersuchungsgebiet in situ und Fernerkundungssysteme wie z.B. Regen- und Wolkenradar, Aerosolmessgeräte, Wasserprobenahmesysteme, ein Infraschallsensor, Energiebilanz- und Eddy-Kovarianz-Stationen, Wolkenkameras, eine Station für Ballonsondierungen sowie Netzwerke aus Windlidaren, Niederschlags-, Hagel- und Bodenfeuchtesensoren von den Projektbeteiligten installiert und betrieben. Zum Messkonzept gehörten zudem die Forschungsflugzeuge D-ILAB, D-IBUF und D-CFFU, der UFZ-Rover zur Messung der Bodenfeuchte mittels Neutronensensoren und kleine Schwarmsonden, die ein Team aus "Gewitterjägern" im unmittelbaren Vorfeld von Gewittern startete. Präsentiert werden zum einen das Konzept des interdisziplinären Forschungsprojekts und die abgestimmten Messstrategien der verschiedenen beteiligten Gruppen. Zum anderen wird ein Überblick über die zugrundeliegenden wissenschaftlichen Fragestellungen und Ziele gegeben und diese anhand erster Messergebnisse veranschaulicht. Zu den Fragestellungen und Zielen, die auch die Standorte der Messgeräte bestimmten, gehören unter anderem die Rolle der topografischen Strömungsmodifikation auf die Gewitterauslösung sowie der Einfluss von Aerosolpartikeln (z.B. Saharastaub) auf die Veränderung der atmosphärischen Stabilität und die Entstehung konvektiver Zellen. Weiterhin erlaubt das dichte Messnetz die Untersuchung der Inhomogenität von Starkregen, Hagel und Bodenfeuchte bei konvektiven Ereignissen. Wie der Einsatz der teils neuartigen mobilen Messsysteme zeigt, nimmt neben den inhaltlichen hydro-meteorologischen Forschungsfragen auch die (Weiter-)Entwicklung neuer Messtechniken einen wichtigen Platz in der Messkampagne ein. Zum Abschluss wird ein Ausblick auf die geplante Folgekampagne im Jahr 2023 gegeben, an der weitere Forschungspartner teilnehmen können.