The growth of freshly formed aerosol particles can be the bottleneck in their survival to cloud condensation nuclei. It is therefore crucial to understand how particles grow in the atmosphere. Insufficient experimental data has impeded a profound understanding of nano-particle growth under atmospheric conditions. Here we study nano-particle growth in the CLOUD (Cosmics Leaving OUtdoors Droplets) chamber, starting from the formation of molecular clusters. We present measured growth rates at sub-3 nm sizes with different atmospherically relevant concentrations of sulphuric acid, water, ammonia and dimethylamine. We find that atmospheric ions and small acid-base clusters, which are not generally accounted for in the measurement of sulphuric acid vapour, can participate in the growth process, leading to enhanced growth rates. The availability of compounds capable of stabilizing sulphuric acid clusters governs the magnitude of these effects and thus the exact growth mechanism. We bring these observations into a coherent framework and discuss their significance in the atmosphere.

, 717 (2014); 344 Science et al. Francesco Riccobono of Atmospheric Particles Oxidation Products of Biogenic Emissions Contribute to Nucleation This copy is for your personal, non-commercial use only. clicking here. colleagues, clients, or customers by , you can order high-quality copies for your If you wish to distribute this article to others here. following the guidelines can be obtained by Permission to republish or repurpose articles or portions of articles ): May 18, 2014 www.sciencemag.org (this information is current as of The following resources related to this article are available online at http://www.sciencemag.org/content/344/6185/717.full.html version of this article at: including high-resolution figures, can be found in the online Updated information and services, http://www.sciencemag.org/content/suppl/2014/05/14/344.6185.717.DC1.html can be found at: Supporting Online Material http://www.sciencemag.org/content/344/6185/717.full.html#ref-list-1 , 9 of which can be accessed free: cites 68 articles This article http://www.sciencemag.org/cgi/collection/atmos Atmospheric Science subject collections: This article appears in the following

Atmospheric new-particle formation affects climate and is one of the least understood atmospheric aerosol processes. The complexity and variability of the atmosphere has hindered elucidation of the fundamental mechanism of new-particle formation from gaseous precursors. We show, in experiments performed with the CLOUD (Cosmics Leaving Outdoor Droplets) chamber at CERN, that sulfuric acid and oxidized organic vapors at atmospheric concentrations reproduce particle nucleation rates observed in the lower atmosphere. The experiments reveal a nucleation mechanism involving the formation of clusters containing sulfuric acid and oxidized organic molecules from the very first step. Inclusion of this mechanism in a global aerosol model yields a photochemically and biologically driven seasonal cycle of particle concentrations in the continental boundary layer, in good agreement with observations.

The first experimental study on the temperature dependence (263-288 K) of heterogeneous nucleation of water vapor on neutral insoluble Ag and soluble NaCl particles (3.5-8 nm) is presented. Heterogeneous nucleation probability was measured as a function of saturation ratio for different seed particle diameters and nucleation temperatures by means of an expansion type condensation particle counter (CPC) - the Size Analyzing Nuclei Counter (SANC). Water vapor onset saturation ratios were also determined. Results revealed an unusual temperature trend for Ag particles, while the temperature effect for NaCl seeds was found to be in qualitative agreement with theory. In order to exclude potential experimental artifacts the effect of temperature on homogeneous nucleation of water vapor was investigated as well and agreement with theoretical predictions was observed.

We present a newly developed expansion chamber condensation particle counter - the versatile Size Analyzing Nuclei Counter (vSANC) - applicable for both laboratory as well as field measurements.The vSANC was optimized to achieve high flexibility in investigating aerosol particles from diameters of 1-2nm upwards at temperatures ranging from -20 degrees C to +40 degrees C and gas pressures ranging from 0.2 bar to 1.2 bar. The operation is based on heterogeneous nucleation of well-defined uniform supersaturated vapor on particles and subsequent droplet growth. Thereby particles, which are initially too small to be detected, grow to visible sizes. Starting from diameters of about 120nm they can be observed with an optical detection method - the multiple Constant Angle Mie Scattering method. This enables automated determination of droplet growth rates for precision verification of vapor supersaturation ranging from 5% up to the limit of homogeneous nucleation as well as absolute number concentrations ranging from 50/cc to 10(7)/cc, independent from the aerosol flow.

Nucleation of aerosol particles from trace atmospheric vapours is thought to provide up to half of global cloud condensation nuclei. Aerosols can cause a net cooling of climate by scattering sunlight and by leading to smaller but more numerous cloud droplets, which makes clouds brighter and extends their lifetimes. Atmospheric aerosols derived from human activities are thought to have compensated for a large fraction of the warming caused by greenhouse gases. However, despite its importance for climate, atmospheric nucleation is poorly understood. Recently, it has been shown that sulphuric acid and ammonia cannot explain particle formation rates observed in the lower atmosphere. It is thought that amines may enhance nucleation, but until now there has been no direct evidence for amine ternary nucleation under atmospheric conditions. Here we use the CLOUD (Cosmics Leaving OUtdoor Droplets) chamber at CERN and find that dimethylamine above three parts per trillion by volume can enhance particle formation rates more than 1,000-fold compared with ammonia, sufficient to account for the particle formation rates observed in the atmosphere. Molecular analysis of the clusters reveals that the faster nucleation is explained by a base-stabilization mechanism involving acid-amine pairs, which strongly decrease evaporation. The ion-induced contribution is generally small, reflecting the high stability of sulphuric acid-dimethylamine clusters and indicating that galactic cosmic rays exert only a small influence on their formation, except at low overall formation rates. Our experimental measurements are well reproduced by a dynamical model based on quantum chemical calculations of binding energies of molecular clusters, without any fitted parameters. These results show that, in regions of the atmosphere near amine sources, both amines and sulphur dioxide should be considered when assessing the impact of anthropogenic activities on particle formation.

First order phase transitions involve nucleation, formation of nanoscale regions of a new phase within a metastable parent phase. Using the heterogeneous nucleation theorem we show how clusters formed by nucleation on single molecules evolve from the gas phase and determine the critical size beyond which condensation starts to form aerosol particles. Our experiments reveal the activation of molecules into droplets to happen via formation of critical clusters substantially larger than the seed molecule. The nanosized critical clusters were found to be well predicted by the Kelvin-Thomson relation pointing directly to the key step in the phase transition.

The concept of the life supporting zone is a generalization of the concept of the habitable zone (and therefore for water based life, i.e. life-as-we-know-it) to other solvents (and to life-as-we-do-not-know-it). We present an estimate of life supporting zones of Kepler-22b and the Kepler planetary candidates KOI268.01, KOI701.03, KOI854.01 and KOI1026.01. The life supporting zone envelopes in this study the water, sulfuric acid and water/ammonia mixture habitable zones. Planetary surface temperatures were computed with a radiative convective model for "Venus-like" and "Earth-like" atmospheric scenarios including clouds. For Kepler-22b an Earth-like planet and an ocean planet (50 wt% H2O) scenario are investigated. Restrictions on stellar and planetary input parameters are derived from the model simulations. The input parameters with the largest influence on planetary surface temperature are the stellar flux, the planets' surface albedo, the considered atmospheric scenario and cloud properties. Water and thick H2SO4-clouds lead to lower surface temperatures for small values of surface albedos and higher temperatures for higher albedos. For thin H2SO4-clouds the cooling effect dominates. All planet(ary candidate)s investigated are likely to lie in the life supporting zone. Kepler-22b and KOI701.03 are likely to lie in the water habitable zone.

Atmospheric aerosols exert an important influence on climate through their effects on stratiform cloud albedo and lifetime and the invigoration of convective storms. Model calculations suggest that almost half of the global cloud condensation nuclei in the atmospheric boundary layer may originate from the nucleation of aerosols from trace condensable vapours, although the sensitivity of the number of cloud condensation nuclei to changes of nucleation rate may be small. Despite extensive research, fundamental questions remain about the nucleation rate of sulphuric acid particles and the mechanisms responsible, including the roles of galactic cosmic rays and other chemical species such as ammonia. Here we present the first results from the CLOUD experiment at CERN. We find that atmospherically relevant ammonia mixing ratios of 100 parts per trillion by volume, or less, increase the nucleation rate of sulphuric acid particles more than 100-1,000-fold. Time-resolved molecular measurements reveal that nucleation proceeds by a base-stabilization mechanism involving the stepwise accretion of ammonia molecules. Ions increase the nucleation rate by an additional factor of between two and more than ten at ground-level galactic-cosmic-ray intensities, provided that the nucleation rate lies below the limiting ion-pair production rate. We find that ion-induced binary nucleation of H(2)SO(4)-H(2)O can occur in the mid-troposphere but is negligible in the boundary layer. However, even with the large enhancements in rate due to ammonia and ions, atmospheric concentrations of ammonia and sulphuric acid are insufficient to account for observed boundary-layer nucleation.

Unary and binary heterogeneous nucleation has been studied experimentally using monodisperse tungsten oxide (WOx) particles in the size range from 1.4 nm up to 7 nm. WOx particles were generated using a commercially available WOx generator in combination with a nanoDMA for size selection. n-Propanol and n-nonane as well as mixtures thereof were used as the nucleating substances. The experiments were performed with an expansion-type condensation particle counter in combination with a constant-angle Mie scattering detector providing counting efficiency of 100% down to at least 3 nm particle diameter. The binary n-propanol–n-nonane system was found to co-nucleate only reluctantly which is in agreement with homogeneous nucleation experiments as well as composition of critical clusters as determined by the heterogeneous nucleation theorem. The size dependent measurements for the pure systems revealed that n-nonane leads to contamination of the chamber at particle sizes below 4 nm. In contrast, n-propanol is suitable to detect particles as small as 1.4 nm.

A radiative convective model to calculate the width and the location of the life supporting zone (LSZ) for different, alternative solvents (i.e. other than water) is presented. This model can be applied to the atmospheres of the terrestrial planets in the solar system as well as (hypothetical, Earth-like) terrestrial exoplanets. Cloud droplet formation and growth are investigated using a cloud parcel model. Clouds can be incorporated into the radiative transfer calculations. Test runs for Earth, Mars and Titan show a good agreement of model results with observations.

In this paper we present the results of contact angle measurements between n-propanol and silver substrates in the temperature range from -10 degrees C to 30 degrees C. The interest in a potential temperature dependence of contact angles originates from recent experiments by S. Schobesberger et al. (Schobesberger S., Strange temperature dependence observed for heterogeneous nucleation of n-propanol vapor on NaCl particles. Master's thesis, University of Vienna, 2008; Schobesberger S. et al., Experiments on the temperature dependence of heterogeneous nucleation on NaCl and Ag particles. In preparation.) investigating the temperature dependence for heterogeneous nucleation of n-propanol vapour on NaCl and on silver particles.We determined dynamic advancing theta(a) and receding theta(r) angles on variously prepared silver probes. The Dynamic Wilhelmy method (Wilhelmy L. Uber die Abhangigkeit der Capillaritats-Constanten des Alkohols von Substanz und Gestalt des benetzten festen Korpers. Ann. Phys. Chem., 199:177-217, 1863) was applied using a Kruss K12 Tensiometer, with a refrigerated double-walled glass top. With respect to its potential influence on heterogeneous nucleation mainly the advancing angle is of interest.The uniform probe geometry required was achieved by accurate cutting and by multiple polishing stages up to the accomplishment of a 0.04 mu m grain size. The original probes consist of 925 sterling silver including a 7.5% copper content. Additional coating with silver pro Analysi (p.A.) was applied making use of pure silver powder evaporation process via Physical Vapour Deposition (PVD).Results show that a surface contamination by copper cannot be neglected for the specification of contact angles. It turned out that additional PVD coatings not only change the values of theta(a) but also their temperature dependence. With increasing the number of coatings of a plate the contact angle decreases and its temperature dependence inverts. Since the contact angle hysteresis theta(hyst) obtained for the variously often coated probes remained practically constant possible changes in surface roughness with increasing number of PVD layers could be excluded. (C) 2010 Elsevier B.V. All rights reserved.

Experimental investigations on the activation of NaCl and Ag aerosol particles by heterogeneous nucleation of n-propanol vapor at well-defined vapor saturation ratios are presented. Particular emphasis is placed on the temperature dependence of this process from -11 to +14 °C. Aerosols are generated in a tube furnace and electrostatically classified at mean geometric mobility equivalent diameters between 3.6 and 11 nm. Activation probabilities are measured by means of expansion chamber experiments, and onset n-propanol saturation ratios are subsequently determined. The experiments with Ag particles do not produce any unexpected results. The results for NaCl particles, however, show a temperature trend of the onset saturation ratios that is opposite to that predicted by classical nucleation theory. This stresses the important role that surface properties play in heterogeneous nucleation processes. By tentatively assuming a temperature-dependent contact angle, we are able to theoretically reproduce this reversed temperature trend. In addition, the shrinkage of NaCl condensation particles is investigated for varying amounts of n-propanol vapor, and contact angle measurements are performed at temperatures ranging from -7 to +30 °C.

Generation, investigation, and manipulation of nanostructured materials are of fundamental and practical importance for several disciplines, including materials science and medicine. Recently, atmospheric new particle formation in the nanometer-size range has been found to be a global phenomenon. Still, its detailed mechanisms are mostly unknown, largely depending on the incapability to generate and measure nanoparticles in a controlled way. In our experiments, an organic vapor (n-propanol) condenses on molecular ions, as well as on charged and uncharged inorganic nanoparticles, via initial activation by heterogeneous nucleation. We found a smooth transition in activation behavior as a function of size and activation to occur well before the onset of homogeneous nucleation. Furthermore, nucleation enhancement for charged particles and a substantial negative sign preference were quantitatively detected.

Heterogeneous nucleation of supersaturated n-nonane vapour on seed particles of different size and composition has been investigated using a fast expansion chamber. Monodisperse seed particle sizes were ranging from about 4 nm up to about 24 nm in diameter. By using different types of particle generators WOx, Ag and (NH4)(2)SO4 particles were generated. For direct comparison between different particle compositions overlapping sizes have been generated for WO, and Ag at about 7 nm particle diameter as well as for Ag and (NH4)(2)SO4 at about 15 nm. Nucleation temperature was kept constant at about 278 K. Experimental data were compared to Kelvin equation and Fletcher theory including the effect of line tension. it was found that heterogeneous nucleation of n-nonane seems to be independent of seed particle composition and starts well below the Kelvin curve. Good agreement was achieved with Fletcher theory including the effect of line tension. (c) 2008 Elsevier B.V. All rights reserved.

Particle detection by condensation particle counters (CPCs) is ultimately limited by the onset of homogeneous nucleation. At vapour supersaturations around the homogeneous nucleation limit the diameter of critical clusters is typically about 2 nm. It is widely assumed that only particles larger than critical clusters can be activated by vapour condensation and the general detection limit of CPCs is therefore currently accepted to be around 2 nm particle diameter. Using an expansion type CPC with n-propanol as working fluid we investigated the transition from heterogeneous to homogeneous nucleation, clearly showing that particles are activated much before the onset of homogeneous nucleation, even at particle diameters as small as 1.4 nm. For particle diameters below 2 nm we have usually found condensation particle counting to be influenced by the simultaneous presence of ions as generated in a bipolar diffusion charger. In this paper we illustrate how the presence of ions influences particle number concentration measurement and how ions can be removed in order to obtain accurate seed particle number concentrations for particle diameters down to 1 nm. (c) 2008 Elsevier B.V. All rights reserved.

Heterogeneous nucleation probabilities for nucleation of n-propanol vapor on positive and negative ions around 1 nm electrical mobility diameter were experimentally determined using a fast expansion chamber. Ions were obtained from a 241Am bipolar diffusion charger and subsequently classified by means of a newly developed Differential Mobility Analyzer (DMA) especially designed for operation in the few nanometer and even subnanometer size range. Although positive and negative ions exhibit clearly different mobility diameters, the corresponding onset saturation ratios were found to be surprisingly similar.