Direct observations of atmospheric aerosol nucleation.
22 Feb 2013-Science (American Association for the Advancement of Science)-Vol. 339, Iss: 6122, pp 943-946
TL;DR: Three separate size regimes below 2-nm diameter are identified that build up a physically, chemically, and dynamically consistent framework on atmospheric nucleation—more specifically, aerosol formation via neutral pathways.
Abstract: Atmospheric nucleation is the dominant source of aerosol particles in the global atmosphere and an important player in aerosol climatic effects. The key steps of this process occur in the sub–2-nanometer (nm) size range, in which direct size-segregated observations have not been possible until very recently. Here, we present detailed observations of atmospheric nanoparticles and clusters down to 1-nm mobility diameter. We identified three separate size regimes below 2-nm diameter that build up a physically, chemically, and dynamically consistent framework on atmospheric nucleation—more specifically, aerosol formation via neutral pathways. Our findings emphasize the important role of organic compounds in atmospheric aerosol formation, subsequent aerosol growth, radiative forcing and associated feedbacks between biogenic emissions, clouds, and climate.
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TL;DR: It is found that a direct pathway leads from several biogenic VOCs, such as monoterpenes, to the formation of large amounts of extremely low-volatility vapours, helping to explain the discrepancy between the observed atmospheric burden of secondary organic aerosol and that reported by many model studies.
Abstract: Forests emit large quantities of volatile organic compounds (VOCs) to the atmosphere. Their condensable oxidation products can form secondary organic aerosol, a significant and ubiquitous component of atmospheric aerosol, which is known to affect the Earth's radiation balance by scattering solar radiation and by acting as cloud condensation nuclei. The quantitative assessment of such climate effects remains hampered by a number of factors, including an incomplete understanding of how biogenic VOCs contribute to the formation of atmospheric secondary organic aerosol. The growth of newly formed particles from sizes of less than three nanometres up to the sizes of cloud condensation nuclei (about one hundred nanometres) in many continental ecosystems requires abundant, essentially non-volatile organic vapours, but the sources and compositions of such vapours remain unknown. Here we investigate the oxidation of VOCs, in particular the terpene α-pinene, under atmospherically relevant conditions in chamber experiments. We find that a direct pathway leads from several biogenic VOCs, such as monoterpenes, to the formation of large amounts of extremely low-volatility vapours. These vapours form at significant mass yield in the gas phase and condense irreversibly onto aerosol surfaces to produce secondary organic aerosol, helping to explain the discrepancy between the observed atmospheric burden of secondary organic aerosol and that reported by many model studies. We further demonstrate how these low-volatility vapours can enhance, or even dominate, the formation and growth of aerosol particles over forested regions, providing a missing link between biogenic VOCs and their conversion to aerosol particles. Our findings could help to improve assessments of biosphere-aerosol-climate feedback mechanisms, and the air quality and climate effects of biogenic emissions generally.
1,340 citations
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Goethe University Frankfurt1, CERN2, University of Helsinki3, Paul Scherrer Institute4, University of Beira Interior5, University of Innsbruck6, Carnegie Mellon University7, California Institute of Technology8, University of Leeds9, University of Eastern Finland10, University of Vienna11, Lebedev Physical Institute12, Finnish Meteorological Institute13, Kyoto University14, Helsinki Institute of Physics15, Stockholm University16, Leibniz Association17
TL;DR: The 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.
Abstract: Nucleation of aerosol particles from trace atmospheric vapours is thought to provide up to half of global cloud condensation nuclei(1). Aerosols can cause a net cooling of climate by scattering sun ...
738 citations
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TL;DR: The literature on atmospheric particulate maffer (PM), or atmospheric aerosol, has increased enormously over the last 2 decades and amounts now to some 1500-2000 papers per year in the refereed literature.
Abstract: The literature on atmospheric particulate maffer (PM), or atmospheric aerosol, has increased enormously over the last 2 decades and amounts now to some 1500—2000 papers per year in the refereed literature. This is in part due to the enormous advances in measurement technologies, which have allowed for an increasingly accurate understanding of the chemical composition and of the physical properties of atmospheric particles and of their processes in the atmosphere. The growing scientific interest in atmospheric aerosol particles is due to their high importance for environmental policy. In fact, particulate maffer constitutes one of the most challenging problems both for air quality and for climate change policies. In this context, this paper reviews the most recent results within the atmospheric aerosol sciences and thepoticy needs, which have driven much ofthe increase in monitoring and mechanistic research over the last 2 decades. The synthesis reveals many new processes and developments in the science underpinning climate—aerosol interactions and effects of PM on human health and the environment. However, while airborne particulate matter is responsible for globally important influences on premature human mortality, we stijl do not know the relative importance of the different chemical components of PM for these effects. Likewise, the magnitude of the overall effects of PM on climate remains highly uncertain. Despite the uncertainty there are many things that could be done to mitigate local and global problems of atmospheric PM. Recent analyses have shown that reducing black carbon (BC) emissions, using known control measures, would reduce global wanning and delay the time when anthropogenic effects on global temperature would exceed 2°C. Likewise, cost-effective control measures on ammonia, an important agricultural precursor gas for secondary inorganic aerosols (SlA), would reduce regional eutrophication and PM concentrations in large areas of Europe, China and the USA. Thus, there is much that could be done to reduce the effects of atmospheric PM on the climate and the health of the environment and the human population. A prioritized list of actions to mitigate the full range of effects ofPM is currently undeliverable due to shortcomings in the knowledge of aerosol science; among the shortcomings, the roles of PM in global climate and the relative roles of different PM precursor sources and their response to climate and land use change over the remaining decades of this century are prominent. In any case, the evidence from this paper strongly advocates for an integrated approach to air quality and climate policies.
648 citations
Cites background from "Direct observations of atmospheric ..."
...Secondary biogenic aerosol does not include only monoterpene, isoprene and sesquiterpene oxidation products but also amines as detected at several sites, including the Boreal forest and the North Atlantic (Facchini et al., 2008; Kulmala et al., 2013)....
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...After being formed at sizes close to 1–2 nm (Kulmala et al., 2007, 2013), the new particles are rapidly lost by coagulation to the larger end of the size distribution (Fig....
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Paul Scherrer Institute1, Carnegie Mellon University2, CERN3, Goethe University Frankfurt4, University of Helsinki5, Stockholm University6, ETH Zurich7, Earth System Research Laboratory8, Cooperative Institute for Research in Environmental Sciences9, California Institute of Technology10, Helsinki Institute of Physics11, University of Innsbruck12, University of Eastern Finland13, Finnish Meteorological Institute14, National Center for Atmospheric Research15, Karlsruhe Institute of Technology16, University of Leeds17, University of California, Irvine18, University of Vienna19, University of Beira Interior20
TL;DR: It is shown that organic vapours alone can drive nucleation, and a particle growth model is presented that quantitatively reproduces the measurements and implements a parameterization of the first steps of growth in a global aerosol model that can change substantially in response to concentrations of atmospheric cloud concentration nuclei.
Abstract: About half of present-day cloud condensation nuclei originate from atmospheric nucleation, frequently appearing as a burst of new particles near midday. Atmospheric observations show that the growth rate of new particles often accelerates when the diameter of the particles is between one and ten nanometres. In this critical size range, new particles are most likely to be lost by coagulation with pre-existing particles, thereby failing to form new cloud condensation nuclei that are typically 50 to 100 nanometres across. Sulfuric acid vapour is often involved in nucleation but is too scarce to explain most subsequent growth, leaving organic vapours as the most plausible alternative, at least in the planetary boundary layer. Although recent studies predict that low-volatility organic vapours contribute during initial growth, direct evidence has been lacking. The accelerating growth may result from increased photolytic production of condensable organic species in the afternoon, and the presence of a possible Kelvin (curvature) effect, which inhibits organic vapour condensation on the smallest particles (the nano-Kohler theory), has so far remained ambiguous. Here we present experiments performed in a large chamber under atmospheric conditions that investigate the role of organic vapours in the initial growth of nucleated organic particles in the absence of inorganic acids and bases such as sulfuric acid or ammonia and amines, respectively. Using data from the same set of experiments, it has been shown that organic vapours alone can drive nucleation. We focus on the growth of nucleated particles and find that the organic vapours that drive initial growth have extremely low volatilities (saturation concentration less than 10(-4.5) micrograms per cubic metre). As the particles increase in size and the Kelvin barrier falls, subsequent growth is primarily due to more abundant organic vapours of slightly higher volatility (saturation concentrations of 10(-4.5) to 10(-0.5) micrograms per cubic metre). We present a particle growth model that quantitatively reproduces our measurements. Furthermore, we implement a parameterization of the first steps of growth in a global aerosol model and find that concentrations of atmospheric cloud concentration nuclei can change substantially in response, that is, by up to 50 per cent in comparison with previously assumed growth rate parameterizations.
507 citations
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Goethe University Frankfurt1, CERN2, University of Helsinki3, Helsinki Institute of Physics4, University of Leeds5, Paul Scherrer Institute6, University of Washington7, University of Innsbruck8, University of Lisbon9, ETH Zurich10, California Institute of Technology11, University of Eastern Finland12, Finnish Meteorological Institute13, Lebedev Physical Institute14, Stockholm University15, University of Vienna16, Leibniz Association17, University of Beira Interior18, Carnegie Mellon University19
TL;DR: Ion-induced nucleation of pure organic particles constitutes a potentially widespread source of aerosol particles in terrestrial environments with low sulfuric acid pollution.
Abstract: Atmospheric aerosols and their effect on clouds are thought to be important for anthropogenic radiative forcing of the climate, yet remain poorly understood. Globally, around half of cloud condensation nuclei originate from nucleation of atmospheric vapours. It is thought that sulfuric acid is essential to initiate most particle formation in the atmosphere, and that ions have a relatively minor role. Some laboratory studies, however, have reported organic particle formation without the intentional addition of sulfuric acid, although contamination could not be excluded. Here we present evidence for the formation of aerosol particles from highly oxidized biogenic vapours in the absence of sulfuric acid in a large chamber under atmospheric conditions. The highly oxygenated molecules (HOMs) are produced by ozonolysis of α-pinene. We find that ions from Galactic cosmic rays increase the nucleation rate by one to two orders of magnitude compared with neutral nucleation. Our experimental findings are supported by quantum chemical calculations of the cluster binding energies of representative HOMs. Ion-induced nucleation of pure organic particles constitutes a potentially widespread source of aerosol particles in terrestrial environments with low sulfuric acid pollution.
502 citations
References
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TL;DR: In this paper, the formation rate of 3-nm particles is often in the range 0.01-10 cm −3 s −1 in the boundary layer in urban areas and in coastal areas and industrial plumes.
2,028 citations
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TL;DR: Nucleation and Growth of Nanoparticles in the Atmosphere Renyi Zhang,* Alexei Khalizov, Lin Wang, Min Hu, and Wen Xu.
Abstract: Nucleation and Growth of Nanoparticles in the Atmosphere Renyi Zhang,* Alexei Khalizov, Lin Wang, Min Hu, and Wen Xu Department of Atmospheric Sciences andDepartment of Chemistry, Center for Atmospheric Chemistry and Environment, Texas A&M University, College Station, Texas 77843, United States Department of Environmental Science & Engineering and Institute of Global Environment Change Research, Fudan University, Shanghai 200433, China State Key Laboratory of Environmental Simulation and Pollution Control, College of Environmental Sciences and Engineering, Peking University, Beijing, 100871, China
920 citations
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TL;DR: In this paper, the stationary charge distribution on aerosol particles in a symmetrical bipolar ionic atmosphere was determined by the "limiting sphere" method, allowing for the jump in ion concentration at the surface of the particles.
Abstract: By the «limiting sphere» method the combination coefficients for gaseous ions and aerosol particles were calculated, allowing for the jump in ion concentration at the surface of the particles. Hence the stationary charge distribution on aerosol particles in a symmetrical bipolar ionic atmosphere was determined. The use of the Boltzmann equation for this purpose proposed by some authors is theoretically wrong asthis equation applies to equilibrium rather than to stationary states. In practice, the Boltzmann equation can be used for particles with radius ≥3·10−5 cm (under atmospheric pressure). Within this range the image forces and the jump in ion concentration may be neglected. The conditions of the applicability of the steady diffusion equations to the theory of the stationary charge distribution in aerosols are discussed.
709 citations
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TL;DR: In this paper, the authors analyzed size distributions measured continuously at a boreal forest measurement site at Hyytiala, Finland between 1996 and 2003 and identified days when new aerosol particle formation was taking place as well as days when no formation was detected, removing days with ambiguous status.
Abstract: We analyzed size distributions measured continuously at a boreal forest measurement site at Hyytiala, Finland between 1996 and 2003. From the eight-year data we identified days when new aerosol particle formation was taking place as well as days when no formation was detected, removing days with ambiguous status. The event days were then classified based on whether it was possible to determine formation and growth rates of new particles. These characteristics were then calculated. We found that new particle formation happens frequently in the boreal forest boundary layer, with at least 24% of days containing an event. Events are more probable during spring and autumn than during other times of the year. The average formation rate of particles larger than 3 nm was 0.8 cm -3 s -1 , with enhanced rates during spring and autumn. The mean growth rate was 3.0 nm h -1 , peaking in summer. The created event database is valuable for future studies of reasons leading to new particle formation in the atmosphere.
708 citations