Open questions on atmospheric nanoparticle growth

Yli-Juuti, T; Mohr, C; Riipinen, I
Cloud droplets form in the atmosphere on aerosol particles, many of which result from nucleation of vapors. Here the authors comment on current knowledge and open questions regarding the condensational growth of nucleated particles to sizes where they influence cloud formation.

Overview: Integrative and Comprehensive Understanding on Polar Environments (iCUPE) – concept and initial results

Petaja, T; Duplissy, EM; Tabakova, K; Schmale, J; Altstadter, B; Ancellet, G; Arshinov, M; Balin, Y; Baltensperger, U; Bange, J; Beamish, A; Belan, B; Berchet, A; Bossi, R; Cairns, WRL; Ebinghaus, R; El Haddad, I; Ferreira-Araujo, B; Franck, A; Huang, L; Hyvarinen, A; Humbert, A; Kalogridis, AC; Konstantinov, P; Lampert, A; MacLeod, M; Magand, O; Mahura, A; Marelle, L; Masloboev, V; Moisseev, D; Moschos, V; Neckel, N; Onishi, T; Osterwalder, S; Ovaska, A; Paasonen, P; Panchenko, M; Pankratov, F; Pernov, JB; Platis, A; Popovicheva, O; Raut, JC; Riandet, A; Sachs, T; Salvatori, R; Salzano, R; Schroder, L; Schon, M; Shevchenko, V; Skov, H; Sonke, JE; Spolaor, A; Stathopoulos, VK; Strahlendorff, M; Thomas, JL; Vitale, V; Vratolis, S; Barbante, C; Chabrillat, S; Dommergue, A; Eleftheriadis, K; Heilimo, J; Law, KS; Massling, A; Noe, SM; Paris, JD; Prevot, ASH; Riipinen, I; Wehner, B; Xie, ZY; Lappalainen, HK
2020 | Atmos. Chem. Phys. | 20 (14) (8551-8592)
The role of polar regions is increasing in terms of megatrends such as globalization, new transport routes, demography, and the use of natural resources with consequent effects on regional and transported pollutant concentrations. We set up the ERA-PLANET Strand 4 project "iCUPE - integrative and Comprehensive Understanding on Polar Environments" to provide novel insights and observational data on global grand challenges with an Arctic focus. We utilize an integrated approach combining in situ observations, satellite remote sensing Earth observations (EOs), and multi-scale modeling to synthesize data from comprehensive long-term measurements, intensive campaigns, and satellites to deliver data products, metrics, and indicators to stakeholders concerning the environmental status, availability, and extraction of natural resources in the polar areas. The iCUPE work consists of thematic state-of-the-art research and the provision of novel data in atmospheric pollution, local sources and transboundary transport, the characterization of arctic surfaces and their changes, an assessment of the concentrations and impacts of heavy metals and persistent organic pollutants and their cycling, the quantification of emissions from natural resource extraction, and the validation and optimization of satellite Earth observation (EO) data streams. In this paper we introduce the iCUPE project and summarize initial results arising out of the integration of comprehensive in situ observations, satellite remote sensing, and multi-scale modeling in the Arctic context.

Rapid growth of new atmospheric particles by nitric acid and ammonia condensation

Wang, MY; Kong, WM; Marten, R; He, XC; Chen, DX; Pfeifer, J; Heitto, A; Kontkanen, J; Dada, L; Kurten, A; Yli-Juuti, T; Manninen, HE; Amanatidis, S; Amorim, A; Baalbaki, R; Baccarini, A; Bell, DM; Bertozzi, B; Brakling, S; Brilke, S; Murillo, LC; Chiu, R; Chu, BW; De Menezes, LP; Duplissy, J; Finkenzeller, H; Carracedo, LG; Granzin, M; Guida, R; Hansel, A; Hofbauer, V; Krechmer, J; Lehtipalo, K; Lamkaddam, H; Lampimaki, M; Lee, CP; Makhmutov, V; Marie, G; Mathot, S; Mauldin, RL; Mentler, B; Muller, T; Onnela, A; Partoll, E; Petaja, T; Philippov, M; Pospisilova, V; Ranjithkumar, A; Rissanen, M; Rorup, B; Scholz, W; Shen, JL; Simon, M; Sipila, M; Steiner, G; Stolzenburg, D; Tham, YJ; Tome, A; Wagner, AC; Wang, DYS; Wang, YH; Weber, SK; Winkler, PM; Wlasits, PJ; Wu, YH; Xiao, M; Ye, Q; Zauner-Wieczorek, M; Zhou, XQ; Volkamer, R; Riipinen, I; Dommen, J; Curtius, J; Baltensperger, U; Kulmala, M; Worsnop, DR; Kirkby, J; Seinfeld, JH; El-Haddad, I; Flagan, RC; Donahue, NM
2020 | Nature | 581 (7807) (184-+)
A list of authors and their affiliations appears at the end of the paper New-particle formation is a major contributor to urban smog(1,2), but how it occurs in cities is often puzzling(3). If the growth rates of urban particles are similar to those found in cleaner environments (1-10 nanometres per hour), then existing understanding suggests that new urban particles should be rapidly scavenged by the high concentration of pre-existing particles. Here we show, through experiments performed under atmospheric conditions in the CLOUD chamber at CERN, that below about +5 degrees Celsius, nitric acid and ammonia vapours can condense onto freshly nucleated particles as small as a few nanometres in diameter. Moreover, when it is cold enough (below -15 degrees Celsius), nitric acid and ammonia can nucleate directly through an acid-base stabilization mechanism to form ammonium nitrate particles. Given that these vapours are often one thousand times more abundant than sulfuric acid, the resulting particle growth rates can be extremely high, reaching well above 100 nanometres per hour. However, these high growth rates require the gas-particle ammonium nitrate system to be out of equilibrium in order to sustain gas-phase supersaturations. In view of the strong temperature dependence that we measure for the gas-phase supersaturations, we expect such transient conditions to occur in inhomogeneous urban settings, especially in wintertime, driven by vertical mixing and by strong local sources such as traffic. Even though rapid growth from nitric acid and ammonia condensation may last for only a few minutes, it is nonetheless fast enough to shepherd freshly nucleated particles through the smallest size range where they are most vulnerable to scavenging loss, thus greatly increasing their survival probability. We also expect nitric acid and ammonia nucleation and rapid growth to be important in the relatively clean and cold upper free troposphere, where ammonia can be convected from the continental boundary layer and nitric acid is abundant from electrical storms(4,5).

A Novel Framework to Study Trace Gas Transport in Deep Convective Clouds

Bardakov, R; Riipinen, I; Krejci, R; Savre, J; Thornton, JA; Ekman, AML
Deep convective clouds reach the upper troposphere (8-15 km height). In addition to moisture and aerosol particles, they can bring aerosol precursor gases and other reactive trace gases from the planetary boundary layer to the cloud top. In this paper, we present a method to estimate trace gas transport based on the analysis of individual air parcel trajectories. Large eddy simulation of an idealized deep convective cloud was used to provide realistic environmental input to a parcel model. For a buoyant parcel, we found that the trace gas transport approximately follows one out of three scenarios, determined by a combination of the equilibrium vapor pressure (containing information about water-solubility and pure component saturation vapor pressure) and the enthalpy of vaporization. In one extreme, the trace gas will eventually be completely removed by precipitation. In the other extreme, there is almost no vapor condensation on hydrometeors and most of the gas is transported to the top of the cloud. The scenario in between these two extremes is also characterized by strong gas condensation, but a small fraction of the trace gas may still be transported aloft. This approach confirms previously suggested patterns of inert trace gas behavior in deep convective clouds, agrees with observational data, and allows estimating transport in analytically simple and computationally efficient way compared to explicit cloud-resolving model calculations.

Effect of nucleation on icy pebble growth in protoplanetary discs

Katrin Ros; Anders Johansen; Ilona Riipinen; Daniel Schlesinger
2019 | Astron Astrophys | 629 (A65)

Solid particles in protoplanetary discs can grow by direct vapour deposition outside of ice lines. The presence of microscopic silicate particles may nevertheless hinder growth into large pebbles, since the available vapour is deposited predominantly on the small grains that dominate the total surface area. Experiments on heterogeneous ice nucleation, performed to understand ice clouds in the Martian atmosphere, show that the formation of a new ice layer on a silicate surface requires a substantially higher water vapour pressure than the deposition of water vapour on an existing ice surface. In this paper, we investigate how the difference in partial vapour pressure needed for deposition of vapour on water ice versus heterogeneous ice nucleation on silicate grains influences particle growth close to the water ice line. We developed and tested a dynamical 1D deposition and sublimation model, where we include radial drift, sedimentation, and diffusion in a turbulent protoplanetary disc. We find that vapour is deposited predominantly on already ice-covered particles, since the vapour pressure exterior of the ice line is too low for heterogeneous nucleation on bare silicate grains. Icy particles can thus grow to centimetre-sized pebbles in a narrow region around the ice line, whereas silicate particles stay dust-sized and diffuse out over the disc. The inhibition of heterogeneous ice nucleation results in a preferential region for growth into planetesimals close to the ice line where we find large icy pebbles. The suppression of heterogeneous ice nucleation on silicate grains may also be the mechanism behind some of the observed dark rings around ice lines in protoplanetary discs, as the presence of large ice pebbles outside ice lines leads to a decrease in the opacity there.

Molecular identification of organic vapors driving atmospheric nanoparticle growth

Mohr, C; Thornton, JA; Heitto, A; Lopez-Hilfiker, FD; Lutz, A; Riipinen, I; Hong, J; Donahue, NM; Hallquist, M; Petaja, T; Kulmala, M; Yli-Juuti, T
2019 | Nat. Commun. | 10
aerosol , gas , hyytiala , multifunctional compounds , nucleation mode particles , oxidation , products , size , thermodynamics , volatility
Particles formed in the atmosphere via nucleation provide about half the number of atmospheric cloud condensation nuclei, but in many locations, this process is limited by the growth of the newly formed particles. That growth is often via condensation of organic vapors. Identification of these vapors and their sources is thus fundamental for simulating changes to aerosol-cloud interactions, which are one of the most uncertain aspects of anthropogenic climate forcing. Here we present direct molecular-level observations of a distribution of organic vapors in a forested environment that can explain simultaneously observed atmospheric nanoparticle growth from 3 to 50 nm. Furthermore, the volatility distribution of these vapors is sufficient to explain nanoparticle growth without invoking particle-phase processes. The agreement between observed mass growth, and the growth predicted from the observed mass of condensing vapors in a forested environment thus represents an important step forward in the characterization of atmospheric particle growth.

Interactions between the atmosphere, cryosphere, and ecosystems at northern high latitudes

Boy, M; Thomson, ES; Navarro, JCA; Arnalds, O; Batchvarova, E; Back, J; Berninger, F; Bilde, M; Brasseur, Z; Dagsson-Waldhauserova, P; Castarede, D; Dalirian, M; de Leeuw, G; Dragosics, M; Duplissy, EM; Duplissy, J; Ekman, AML; Fang, KY; Gallet, JC; Glasius, M; Gryning, SE; Grythe, H; Hansson, HC; Hansson, M; Isaksson, E; Iversen, T; Jonsdottir, I; Kasurinen, V; Kirkevag, A; Korhola, A; Krejci, R; Kristjansson, JE; Lappalainen, HK; Lauri, A; Lepparanta, M; Lihavainen, H; Makkonen, R; Massling, A; Meinander, O; Nilsson, ED; Olafsson, H; Pettersson, JBC; Prisle, NL; Riipinen, I; Roldin, P; Ruppel, M; Salter, M; Sand, M; Seland, O; Seppa, H; Skov, H; Soares, J; Stohl, A; Strom, J; Svensson, J; Swietlicki, E; Tabakova, K; Thorsteinsson, T; Virkkula, A; Weyhenmeyer, GA; Wu, YS; Zieger, P; Kulmala, M
2019 | Atmos. Chem. Phys. | 19 (3) (2015-2061)
aerosol-climate interactions , biogenic volatile emissions , black carbon deposition , boreal forest , cloud droplet activation , earth system model , elemental carbon , eurasian experiment peex , organic compounds , sea-ice conditions

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.

Key drivers of cloud response to surface-active organics

Lowe, SJ; Partridge, DG; Davies, JF; Wilson, KR; Topping, D; Riipinen, I
2019 | Nat. Commun. | 10
Aerosol-cloud interactions constitute the largest source of uncertainty in global radiative forcing estimates, hampering our understanding of climate evolution. Recent empirical evidence suggests surface tension depression by organic aerosol to significantly influence the formation of cloud droplets, and hence cloud optical properties. In climate models, however, surface tension of water is generally assumed when predicting cloud droplet concentrations. Here we show that the sensitivity of cloud microphysics, optical properties and shortwave radiative effects to the surface phase are dictated by an interplay between the aerosol particle size distribution, composition, water availability and atmospheric dynamics. We demonstrate that accounting for the surface phase becomes essential in clean environments in which ultrafine particle sources are present. Through detailed sensitivity analysis, quantitative constraints on the key drivers - aerosol particle number concentrations, organic fraction and fixed updraft velocity - are derived for instances of significant cloud microphysical susceptibilities to the surface phase.

The role of highly oxygenated organic molecules in the Boreal aerosol-cloud-climate system

Roldin, P; Ehn, M; Kurten, T; Olenius, T; Rissanen, MP; Sarnela, N; Elm, J; Rantala, P; Hao, LQ; Hyttinen, N; Heikkinen, L; Worsnop, DR; Pichelstorfer, L; Xavier, C; Clusius, P; Ostrom, E; Petaja, T; Kulmala, M; Vehkamaki, H; Virtanen, A; Riipinen, I; Boy, M
2019 | Nat. Commun. | 10
Over Boreal regions, monoterpenes emitted from the forest are the main precursors for secondary organic aerosol (SOA) formation and the primary driver of the growth of new aerosol particles to climatically important cloud condensation nuclei (CCN). Autoxidation of monoterpenes leads to rapid formation of Highly Oxygenated organic Molecules (HOM). We have developed the first model with near-explicit representation of atmospheric new particle formation (NPF) and HOM formation. The model can reproduce the observed NPF, HOM gas-phase composition and SOA formation over the Boreal forest. During the spring, HOM SOA formation increases the CCN concentration by similar to 10 % and causes a direct aerosol radiative forcing of -0.10 W/m(2). In contrast, NPF reduces the number of CCN at updraft velocities < 0.2 m/s, and causes a direct aerosol radiative forcing of +0.15 W/m(2). Hence, while HOM SOA contributes to climate cooling, NPF can result in climate warming over the Boreal forest.

Aerosol Indirect Effects in Marine Stratocumulus: The Importance of Explicitly Predicting Cloud Droplet Activation

Bulatovic, I; Ekman, AML; Savre, J; Riipinen, I; Leck, C
2019 | Geophys Res Lett | 46 (6) (3473-3481)
Climate models generally simulate a unidirectional, positive liquid water path (LWP) response to increasing aerosol number concentration. However, satellite observations and large-eddy simulations show that the LWP may either increase or decrease with increasing aerosol concentration, influencing the overall magnitude of the aerosol indirect effect (AIE). We use large-eddy simulation to investigate the LWP response of a marine stratocumulus cloud and its dependence on different parameterizations for obtaining cloud droplet number concentration (CDNC). The simulations confirm that the LWP response is not always positiveregardless of CDNC treatment. However, the AIE simulated with the model version with prescribed CDNC is almost 3 times larger compared to the version with prognostic CDNC. The reason is that the CDNC in the prognostic scheme varies in time due to supersaturation fluctuations, collection, and other microphysical processes. A substantial spread in simulated AIE may thus arise simply due to the CDNC treatment. Plain Language Summary Our poor understanding of aerosol-cloud-radiation interactions (aerosol indirect effects) results in a major uncertainty in estimates of anthropogenic aerosol forcing. In climate models, the cloud water response to an increased aerosol number concentration may be especially uncertain as models simplify, or do not account for, processes that affect the cloud droplet number concentration and the total amount of cloud water. In this study, we employ large-eddy simulation to explore how different model descriptions for obtaining the number concentration of cloud droplets influences the cloud water response of a marine stratocumulus cloud and thus the simulated aerosol indirect effect. Our simulations show a qualitatively similar cloud water response regardless of model description: the total amount of cloud water increases first and then decreases with increasing aerosol concentration. However, the simulated aerosol indirect effect is almost 3 times as large when the number concentration of cloud droplets is prescribed compared to when it is dependent on the calculated supersaturation and other microphysical processes such as collisions between cloud droplets. Our findings show that a relatively simple difference in the treatment of the number concentration of cloud droplets in climate models may result in a significant spread in the simulated aerosol indirect effect.

Cloud droplet activation of black carbon particles with organic compounds of varying solubility

Dalirian, M.; Ylisirnio, A.; Buchholz, A.; Schlesinger, D.; Strom, J.; Virtanen, A.; Riipinen, I.
2018 | Atmos. Chem. Phys. | 18 (12477-12489)

New particle formation and growth: Creating a new atmospheric phase interface

Olenius, T.; Yli-Juuti, T.; Elm, J.; Kontkanen, J.; Riipinen, I.
2018 | Elsevier Science Publishers | Physical Chemistry of Gas-Liquid Interfaces (315-352) | ISBN: 9780128136416

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