André Welti
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View article: Homogeneous ice nucleation in adsorbed water films: a theoretical approach
Homogeneous ice nucleation in adsorbed water films: a theoretical approach Open
Ice nucleation plays a critical role in cloud formation and atmospheric processes, influencing precipitation and climate. In this study, we present a theoretical approach for describing homogeneous ice nucleation within adsorbed water film…
View article: Ice Nucleating Particle Concentrations over the Eurasian-Arctic seas
Ice Nucleating Particle Concentrations over the Eurasian-Arctic seas Open
Ice nucleating particles (INPs) catalyze primary ice formation in Arctic low-level mixed-phase clouds, influencing their persistence and radiative properties. Knowledge of the abundance, sources, and nature of INPs over the remote Arctic O…
View article: Deposition ice nucleation via homogeneous freezing of adsorbed water
Deposition ice nucleation via homogeneous freezing of adsorbed water Open
Deposition ice nucleation (DIN) occurs when water insoluble particles (that are not immersed in water or aqueous solution droplets) initiate the growth of ice crystals in water vapor supersaturated with respect to ice. The classical view (…
View article: Exploring the processes controlling secondary inorganic aerosol: evaluating the global GEOS-Chem simulation using a suite of aircraft campaigns
Exploring the processes controlling secondary inorganic aerosol: evaluating the global GEOS-Chem simulation using a suite of aircraft campaigns Open
Secondary inorganic aerosols (sulfate, nitrate, and ammonium, SNA) are major contributors to fine particulate matter. Predicting concentrations of these species is complicated by the cascade of processes that control their abundance, inclu…
View article: Homogeneous ice nucleation in adsorbed water films: A theoretical approach
Homogeneous ice nucleation in adsorbed water films: A theoretical approach Open
Ice nucleation plays a critical role in cloud formation and atmospheric processes, influencing precipitation and climate. In this study, we present a theoretical approach for describing homogeneous ice nucleation within adsorbed water film…
View article: A diagonal volatility basis set to assess the condensation of organic vapors onto particles
A diagonal volatility basis set to assess the condensation of organic vapors onto particles Open
We present a “diagonal” Volatility Basis Set (dVBS) comparing gas-phase concentrations of oxygenated organic molecules (OOM) to their condensed-phase mass fractions.
View article: Terrestrial and marine sources of ice nucleating particles in the Eurasian Arctic
Terrestrial and marine sources of ice nucleating particles in the Eurasian Arctic Open
Biogenic ice nucleating particles (INPs) are key over the Arctic Ocean. Significant links between marine biogenic activity, aerosolization, and INP abundance are highlighted, advancing our understanding of ice nucleation for Arctic clouds.
View article: Water Vapor Adsorption–Desorption Hysteresis Due to Clustering of Water on Nonporous Surfaces
Water Vapor Adsorption–Desorption Hysteresis Due to Clustering of Water on Nonporous Surfaces Open
Water vapor is continuously adsorbed onto and desorbed from all kinds of surfaces depending on changes in relative humidity. Adsorption-desorption hysteresis of water that occurs on various nonporous surfaces and extends down to low relati…
View article: Exploring the processes controlling secondary inorganic aerosol: Evaluating the global GEOS-Chem simulation using a suite of aircraft campaigns
Exploring the processes controlling secondary inorganic aerosol: Evaluating the global GEOS-Chem simulation using a suite of aircraft campaigns Open
Secondary inorganic aerosols (sulfate, nitrate, and ammonium; SNA) are major contributors to fine particulate matter. Predicting concentrations of these species is complicated by the cascade of processes that control their abundance, inclu…
View article: Saharan dust in the Finnish atmosphere and on the ground: Citizen science to verify transport and deposition modeling
Saharan dust in the Finnish atmosphere and on the ground: Citizen science to verify transport and deposition modeling Open
Long-range transported mineral dust has a wide range of direct and indirect effects as a pollutant, nutrient and climate-forcer.  On 21–23 February 2021, dust from a sand and dust storm in northern Africa was transported to…
View article: Glucose Enhances Salinity-Driven Sea Spray Aerosol Production in Eastern Arctic Waters
Glucose Enhances Salinity-Driven Sea Spray Aerosol Production in Eastern Arctic Waters Open
Sea spray aerosols (SSA) greatly affect the climate system by scattering solar radiation and acting as seeds for cloud droplet formation. The ecosystems in the Arctic Ocean are rapidly changing due to global warming, and the effects these …
View article: Phase state of water adsorbed on ice nucleating particles
Phase state of water adsorbed on ice nucleating particles Open
Barnes and Sänger (1961) suggested that a substance only becomes active at nucleating ice when the adsorbed water on the surface is in an ice-like state, and that there should be a correspondence between the temperature of ice nucleat…
View article: Insights from a Year-long Study on Ice-Nucleating Particles in Helsinki
Insights from a Year-long Study on Ice-Nucleating Particles in Helsinki Open
This study explores the seasonal dynamics of ice-nucleating particles (INPs) in Helsinki over a year. Using an automatic sampler, we collected atmospheric particle samples daily onto filters, which were subsequently analyzed offline throug…
View article: Investigating the Molecular-Scale Mechanism of Deposition Ice Nucleation on Silver Iodide Surfaces
Investigating the Molecular-Scale Mechanism of Deposition Ice Nucleation on Silver Iodide Surfaces Open
Heterogeneous ice nucleation is a ubiquitous process in the natural and built environment. Deposition ice nucleation, according to the traditional view,, occurs in a subsaturated water vapor environment without the presence of supercooled …
View article: Temperature dependence of cloud drop activation of insoluble particles
Temperature dependence of cloud drop activation of insoluble particles Open
The critical supersaturation of cloud droplet activation by water-soluble aerosols increases at lower temperatures. This is due to the Kelvin effect, with the logarithm of the saturation ratio being inversely proportional to the absolute t…
View article: African dust transport and deposition modelling verified through a successful citizen science campaign in Finland  
African dust transport and deposition modelling verified through a successful citizen science campaign in Finland   Open
On 21–23 February 2021, dust from a sand and dust storm (SDS) in northern Africa was transported to Finland, north of 60°N. The episode was predicted 5 days in advance by the Finnish Meteorological Institute (FMI) global operati…
View article: Cloud drop activation of insoluble particles: impact of surface properties
Cloud drop activation of insoluble particles: impact of surface properties Open
A number of studies have reported experimental CCN activation properties of water insoluble particles, mainly various minerals and soots, during the past decade or so (e.g. Kumar et al., 2011; Lathem et al., 2011, Dalirian et al., 2018). A…
View article: Nitrate Radicals Suppress Biogenic New Particle Formation from Monoterpene Oxidation
Nitrate Radicals Suppress Biogenic New Particle Formation from Monoterpene Oxidation Open
Highly oxygenated organic molecules (HOMs) are a major source of new particles that affect the Earth's climate. HOM production from the oxidation of volatile organic compounds (VOCs) occurs during both the day and night and can lead to new…
View article: The molecular scale mechanism of deposition ice nucleation on silver iodide
The molecular scale mechanism of deposition ice nucleation on silver iodide Open
Schematic of the proposed deposition ice nucleation mechanism on AgI (0001).
View article: Iodine oxoacids enhance nucleation of sulfuric acid particles in the atmosphere
Iodine oxoacids enhance nucleation of sulfuric acid particles in the atmosphere Open
The main nucleating vapor in the atmosphere is thought to be sulfuric acid (H 2 SO 4 ), stabilized by ammonia (NH 3 ). However, in marine and polar regions, NH 3 is generally low, and H 2 SO 4 is frequently found together with iodine oxoac…
View article: African dust transport and deposition modelling verified through a citizen science campaign in Finland
African dust transport and deposition modelling verified through a citizen science campaign in Finland Open
African desert dust is emitted and long-range transported with multiple effects on climate, air quality, cryosphere, and ecosystems. On 21–23 February 2021, dust from a sand and dust storm in northern Africa was transported to Finland, nor…
View article: The chance of freezing – a conceptional study to parameterize temperature-dependent freezing by including randomness of ice-nucleating particle concentrations
The chance of freezing – a conceptional study to parameterize temperature-dependent freezing by including randomness of ice-nucleating particle concentrations Open
Ice-nucleating particle concentrations (INPCs) can spread over several orders of magnitude at any given temperature. However, this variability is rarely accounted for in heterogeneous ice-nucleation parameterizations. In this paper, we pre…
View article: Iodine oxoacids enhance nucleation of sulfuric acid particles in the atmosphere: data resources
Iodine oxoacids enhance nucleation of sulfuric acid particles in the atmosphere: data resources Open
Data resources for manuscript: "Iodine oxoacids enhance nucleation of sulfuric acid particles in the atmosphere"
View article: Iodine oxoacids enhance nucleation of sulfuric acid particles in the atmosphere: data resources
Iodine oxoacids enhance nucleation of sulfuric acid particles in the atmosphere: data resources Open
Data resources for manuscript: "Iodine oxoacids enhance nucleation of sulfuric acid particles in the atmosphere"
View article: Model output from "The chance of freezing – a conceptional study to parameterize temperature-dependent freezing by including randomness of ice-nucleating particle concentrations"
Model output from "The chance of freezing – a conceptional study to parameterize temperature-dependent freezing by including randomness of ice-nucleating particle concentrations" Open
Model output from "The chance of freezing – a conceptional study to parameterize temperature-dependent freezing by including randomness of ice-nucleating particle concentrations", accepted for publication in Atmospheric Chemistry and Physi…
View article: Model output from "The chance of freezing – a conceptional study to parameterize temperature-dependent freezing by including randomness of ice-nucleating particle concentrations"
Model output from "The chance of freezing – a conceptional study to parameterize temperature-dependent freezing by including randomness of ice-nucleating particle concentrations" Open
Model output from "The chance of freezing – a conceptional study to parameterize temperature-dependent freezing by including randomness of ice-nucleating particle concentrations", accepted for publication in Atmospheric Chemistry and Physi…
View article: Measurement of the collision rate coefficients between atmospheric ions and multiply charged aerosol particles in the CERN CLOUD chamber
Measurement of the collision rate coefficients between atmospheric ions and multiply charged aerosol particles in the CERN CLOUD chamber Open
Aerosol particles have an important role in Earth's radiation balance and climate, both directly and indirectly through aerosol–cloud interactions. Most aerosol particles in the atmosphere are weakly charged, affecting both their collision…
View article: An intercomparison study of four different techniques for measuring the chemical composition of nanoparticles
An intercomparison study of four different techniques for measuring the chemical composition of nanoparticles Open
Currently, the complete chemical characterization of nanoparticles (< 100 nm) represents an analytical challenge, since these particles are abundant in number but have negligible mass. Several methods for particle-phase characterization ha…