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1.
Nat Commun ; 10(1): 4442, 2019 09 30.
Artigo em Inglês | MEDLINE | ID: mdl-31570718

RESUMO

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.

2.
Nat Commun ; 10(1): 4370, 2019 09 25.
Artigo em Inglês | MEDLINE | ID: mdl-31554809

RESUMO

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 ~10 % and causes a direct aerosol radiative forcing of -0.10 W/m2. 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/m2. Hence, while HOM SOA contributes to climate cooling, NPF can result in climate warming over the Boreal forest.

3.
Sci Rep ; 8(1): 14160, 2018 Sep 21.
Artigo em Inglês | MEDLINE | ID: mdl-30242199

RESUMO

Comprehensive representation of nanoparticle dynamics is necessary for understanding nucleation and growth phenomena. This is critical in atmospheric physics, as airborne particles formed from vapors have significant but highly uncertain effects on climate. While the vapor-particle mass exchange driving particle growth can be described by a macroscopic, continuous substance for large enough particles, the growth dynamics of the smallest nanoparticles involve stochastic fluctuations in particle size due to discrete molecular collision and decay processes. To date, there have been no generalizable methods for quantifying the particle size regime where the discrete effects become negligible and condensation models can be applied. By discrete simulations of sub-10 nm particle populations, we demonstrate the importance of stochastic effects in the nanometer size range. We derive a novel, theory-based, simple and robust metric for identifying the exact sizes where these effects cannot be omitted for arbitrary molecular systems. The presented metric, based on examining the second- and first-order derivatives of the particle size distribution function, is directly applicable to experimental size distribution data. This tool enables quantifying the onset of condensational growth without prior information on the properties of the vapors and particles, thus allowing robust experimental resolving of nanoparticle formation physics.

4.
Environ Sci Technol ; 52(2): 692-700, 2018 01 16.
Artigo em Inglês | MEDLINE | ID: mdl-29185762

RESUMO

Although they are currently unregulated, atmospheric ultrafine particles (<100 nm) pose health risks because of, e.g., their capability to penetrate deep into the respiratory system. Ultrafine particles, often minor contributors to atmospheric particulate mass, typically dominate aerosol particle number concentrations. We simulated the response of particle number concentrations over Europe to recent estimates of future emission reductions of aerosol particles and their precursors. We used the chemical transport model PMCAMx-UF, with novel updates including state-of-the-art descriptions of ammonia and dimethylamine new particle formation (NPF) pathways and the condensation of organic compounds onto particles. These processes had notable impacts on atmospheric particle number concentrations. All three emission scenarios (current legislation, optimized emissions, and maximum technically feasible reductions) resulted in substantial (10-50%) decreases in median particle number concentrations over Europe. Consistent reductions were predicted in Central Europe, while Northern Europe exhibited smaller reductions or even increased concentrations. Motivated by the improved NPF descriptions for ammonia and methylamines, we placed special focus on the potential to improve air quality by reducing agricultural emissions, which are a major source of these species. Agricultural emission controls showed promise in reducing ultrafine particle number concentrations, although the change is nonlinear with particle size.


Assuntos
Poluentes Atmosféricos , Aerossóis , Aminas , Amônia , Monitoramento Ambiental , Europa (Continente) , Tamanho da Partícula , Material Particulado
6.
J Phys Chem A ; 121(25): 4812-4824, 2017 Jun 29.
Artigo em Inglês | MEDLINE | ID: mdl-28585824

RESUMO

We investigate the effect of the bisulfate anion HSO4-, ammonium cation NH4+, and ammonia NH3 on the clustering of sulfuric acid and pinic acid or 3-methyl-1,2,3-butanetricarboxylic acid (MBTCA). The systems were chosen based on their expected relevance in atmospheric new particle formation. Using quantum chemical methods together with kinetic calculations, we study the ability of these compounds to enhance cluster formation and growth. The cluster structures are obtained and frequencies are calculated using three different DFT functionals (M06-2X, PW91, and ωB97X-D) with the 6-31++G(d,p) basis set. The electronic energies are corrected using an accurate DLPNO-CCSD(T)/def2-QZVPP level of theory. The evaporation rates are evaluated based on the calculated Gibbs free energies. The interaction between the ions and sulfuric acid or carboxylic acid group is strong, and thereby small two-component ionic clusters are found to be very stable against evaporation. The presence of bisulfate stimulates the cluster formation through addition of the sulfuric acid, whereas the presence of ammonium favors the addition of organic acids. Bisulfate and ammonium enhance the first steps of cluster formation; however, at atmospheric conditions further cluster growth is limited due to the weak interaction and fast evaporation of the larger three-component clusters. On the basis of our results it is therefore unlikely that the studied organic acids and sulfuric acid, even together with bisulfate, ammonia, or ammonium can drive new-particle formation via clustering mechanisms. Other mechanisms such as chemical reactions are needed to explain observed new-particle formation events in the presence of oxidized organic compounds resembling the acids studied here.

7.
Environ Sci Technol ; 51(7): 3922-3928, 2017 04 04.
Artigo em Inglês | MEDLINE | ID: mdl-28263597

RESUMO

Phenolic and nitro-aromatic compounds are extremely toxic components of atmospheric aerosol that are currently not well understood. In this Article, solid and subcooled-liquid-state saturation vapor pressures of phenolic and nitro-aromatic compounds are measured using Knudsen Effusion Mass Spectrometry (KEMS) over a range of temperatures (298-318 K). Vapor pressure estimation methods, assessed in this study, do not replicate the observed dependency on the relative positions of functional groups. With a few exceptions, the estimates are biased toward predicting saturation vapor pressures that are too high, by 5-6 orders of magnitude in some cases. Basic partitioning theory comparisons indicate that overestimation of vapor pressures in such cases would cause us to expect these compounds to be present in the gas state, whereas measurements in this study suggest these phenolic and nitro-aromatic will partition into the condensed state for a wide range of ambient conditions if absorptive partitioning plays a dominant role. While these techniques might have both structural and parametric uncertainties, the new data presented here should support studies trying to ascertain the role of nitrogen containing organics on aerosol growth and human health impacts.


Assuntos
Pressão de Vapor , Volatilização , Nitrocompostos , Hidrocarbonetos Policíclicos Aromáticos , Temperatura
8.
Environ Sci Technol ; 50(14): 7434-42, 2016 07 19.
Artigo em Inglês | MEDLINE | ID: mdl-27326704

RESUMO

Atmospheric particulate matter is one of the main factors governing the Earth's radiative budget, but its exact effects on the global climate are still uncertain. Knowledge on the molecular-scale surface phenomena as well as interactions between atmospheric organic and inorganic compounds is necessary for understanding the role of airborne nanoparticles in the Earth system. In this work, surface composition of aqueous model systems containing succinic acid and sodium chloride or ammonium sulfate is determined using a novel approach combining X-ray photoelectron spectroscopy, surface tension measurements and thermodynamic modeling. It is shown that succinic acid molecules are accumulated in the surface, yielding a 10-fold surface concentration as compared with the bulk for saturated succinic acid solutions. Inorganic salts further enhance this enrichment due to competition for hydration in the bulk. The surface compositions for various mixtures are parametrized to yield generalizable results and used to explain changes in surface tension. The enhanced surface partitioning implies an increased maximum solubility of organic compounds in atmospheric nanoparticles. The results can explain observations of size-dependent phase-state of atmospheric nanoparticles, suggesting that these particles can display drastically different behavior than predicted by bulk properties only.


Assuntos
Material Particulado/química , Soluções , Aerossóis/química , Sulfato de Amônio/química , Nanopartículas
9.
Nature ; 533(7604): 521-6, 2016 05 26.
Artigo em Inglês | MEDLINE | ID: mdl-27225125

RESUMO

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.


Assuntos
Aerossóis/química , Atmosfera/química , Mudança Climática , Íons/química , Oxigênio/química , Material Particulado/química , Poluição do Ar/análise , Monoterpenos Bicíclicos , Radiação Cósmica , Atividades Humanas , Monoterpenos/química , Oxirredução , Ozônio/química , Tamanho da Partícula , Teoria Quântica , Ácidos Sulfúricos/análise , Volatilização
11.
Environ Sci Technol ; 48(23): 13718-26, 2014 Dec 02.
Artigo em Inglês | MEDLINE | ID: mdl-25369247

RESUMO

Particulate phase reactions between organic and inorganic compounds may significantly alter aerosol chemical properties, for example, by suppressing particle volatility. Here, chemical processing upon drying of aerosols comprised of organic (acetic, oxalic, succinic, or citric) acid/monovalent inorganic salt mixtures was assessed by measuring the evaporation of the organic acid molecules from the mixture using a novel approach combining a chemical ionization mass spectrometer coupled with a heated flow tube inlet (TPD-CIMS) with kinetic model calculations. For reference, the volatility, i.e. saturation vapor pressure and vaporization enthalpy, of the pure succinic and oxalic acids was also determined and found to be in agreement with previous literature. Comparison between the kinetic model and experimental data suggests significant particle phase processing forming low-volatility material such as organic salts. The results were similar for both ammonium sulfate and sodium chloride mixtures, and relatively more processing was observed with low initial aerosol organic molar fractions. The magnitude of low-volatility organic material formation at an atmospherically relevant pH range indicates that the observed phenomenon is not only significant in laboratory conditions but is also of direct atmospheric relevance.


Assuntos
Aerossóis/química , Ácidos Carboxílicos/química , Espectrometria de Massas/métodos , Ácido Acético/química , Ionização do Ar , Ácido Cítrico/química , Cinética , Modelos Teóricos , Ácido Oxálico/química , Sais , Ácido Succínico/química , Pressão de Vapor , Volatilização
12.
Environ Sci Technol ; 48(23): 13769-75, 2014 Dec 02.
Artigo em Inglês | MEDLINE | ID: mdl-25356879

RESUMO

The effect of ammonia on the partitioning of two dicarboxylic acids, oxalic (C2) and adipic (C6) is determined. Measurements by a tandem differential mobility analysis system and a thermodenuder (TD-TDMA) system are used to estimate the saturation vapor pressure and enthalpy of vaporization of ammonium oxalate and adipate. Ammonia dramatically lowered the vapor pressure of oxalic acid, by several orders of magnitude, with an estimated vapor pressure of 1.7 ± 0.8 × 10(­6) Pa at 298 K. The vapor pressure of ammonium adipate was 2.5 ± 0.8 × 10(­5) Pa at 298 K, similar to that of adipic acid. These results suggest that the dominance of oxalate in diacid concentrations measured in ambient aerosol could be attributed to the salt formation with ammonia.


Assuntos
Adipatos/química , Aerossóis/química , Poluentes Atmosféricos/química , Ácido Oxálico/química , Termodinâmica , Pressão de Vapor , Volatilização
13.
Phys Chem Chem Phys ; 16(39): 21486-95, 2014 Oct 21.
Artigo em Inglês | MEDLINE | ID: mdl-25182698

RESUMO

The water-vapor interface of aqueous solutions of succinic acid, where pH values and bulk concentrations were varied, has been studied using surface sensitive X-ray photoelectron spectroscopy (XPS) and molecular dynamics (MD) simulations. It was found that succinic acid has a considerably higher propensity to reside in the aqueous surface region than its deprotonated form, which is effectively depleted from the surface due to the two strongly hydrated carboxylate groups. From both XPS experiments and MD simulations a strongly increased concentration of the acid form in the surface region compared to the bulk concentration was found and quantified. Detailed analysis of the surface of succinic acid solutions at different bulk concentrations led to the conclusion that succinic acid saturates the aqueous surface at high bulk concentrations. With the aid of MD simulations the thickness of the surface layer could be estimated, which enabled the quantification of surface concentration of succinic acid as a multiple of the known bulk concentration. The obtained enrichment factors were successfully used to model the surface tension of these binary aqueous solutions using two different models that account for the surface enrichment. This underlines the close correlation of increased concentration at the surface relative to the bulk and reduced surface tension of aqueous solutions of succinic acid. The results of this study shed light on the microscopic origin of surface tension, a macroscopic property. Furthermore, the impact of the results from this study on atmospheric modeling is discussed.

14.
Environ Sci Technol ; 48(20): 12083-9, 2014 Oct 21.
Artigo em Inglês | MEDLINE | ID: mdl-25260072

RESUMO

Atmospheric aerosol particles have a significant effect on global climate, air quality, and consequently human health. Condensation of organic vapors is a key process in the growth of nanometer-sized particles to climate relevant sizes. This growth is very sensitive to the mass accommodation coefficient α, a quantity describing the vapor uptake ability of the particles, but knowledge on α of atmospheric organics is lacking. In this work, we have determined α for four organic molecules with diverse structural properties: adipic acid, succinic acid, naphthalene, and nonane. The coefficients are studied using molecular dynamics simulations, complemented with expansion chamber measurements. Our results are consistent with α = 1 (indicating nearly perfect accommodation), regardless of the molecular structural properties, the phase state of the bulk condensed phase, or surface curvature. The results highlight the need for experimental techniques capable of resolving the internal structure of nanoparticles to better constrain the accommodation of atmospheric organics.


Assuntos
Adipatos/química , Alcanos/química , Naftalenos/química , Material Particulado/química , Ácido Succínico/química , Aerossóis/química , Clima , Gases/química , Humanos , Simulação de Dinâmica Molecular , Peso Molecular , Nanopartículas/química , Tamanho da Partícula
15.
Environ Sci Technol ; 48(16): 9298-305, 2014 Aug 19.
Artigo em Inglês | MEDLINE | ID: mdl-25062124

RESUMO

The growth, composition, and evolution of secondary organic aerosol (SOA) are governed by properties of individual compounds and ensemble mixtures that affect partitioning between the vapor and condensed phase. There has been considerable recent interest in the idea that SOA can form highly viscous particles where the diffusion of either water or semivolatile organics within the particle is sufficiently hindered to affect evaporation and growth. Despite numerous indirect inferences of viscous behavior from SOA evaporation or "bounce" within aerosol instruments, there have been no bulk measurements of the viscosity of well-constrained model aerosol systems of atmospheric significance. Here the viscous behavior of a well-defined model system of 9 dicarboxylic acids is investigated directly with complementary measurements and model predictions used to infer phase state. Results not only allow us to discuss the atmospheric implications for SOA formation through this representative mixture, but also the potential impact of current methodologies used for probing this affect in both the laboratory and from a modeling perspective. We show, quantitatively, that the physical state transformation from liquid-like to amorphous semisolid can substantially increase the importance of mass transfer limitations within particles by 7 orders of magnitude for 100 nm diameter particles. Recommendations for future research directions are given.


Assuntos
Aerossóis/química , Poluentes Atmosféricos/química , Modelos Químicos , Ácidos Dicarboxílicos/química , Difusão , Gases , Tamanho da Partícula , Transição de Fase , Viscosidade , Água/química
16.
J Phys Chem A ; 118(14): 2599-611, 2014 Apr 10.
Artigo em Inglês | MEDLINE | ID: mdl-24678924

RESUMO

Formation of new particles through clustering of molecules from condensable vapors is a significant source for atmospheric aerosols. The smallest clusters formed in the very first steps of the condensation process are, however, not directly observable by experimental means. We present here a comprehensive series of electronic structure calculations on the hydrates of clusters formed by up to four molecules of sulfuric acid, and up to two molecules of ammonia or dimethylamine. Though clusters containing ammonia, and certainly dimethylamine, generally exhibit lower average hydration than the pure acid clusters, populations of individual hydrates vary widely. Furthermore, we explore the predictions obtained using a thermodynamic model for the description of these hydrates. The similar magnitude and trends of hydrate formation predicted by both methods illustrate the potential of combining them to obtain more comprehensive models. The stabilization of some clusters relative to others due to their hydration is highly likely to have significant effects on the overall processes that lead to formation of new particles in the atmosphere.


Assuntos
Atmosfera/química , Simulação de Dinâmica Molecular , Termodinâmica , Aerossóis/química , Amônia/química , Dimetilaminas/química , Elétrons , Ácidos Sulfúricos/química , Água/química
17.
Top Curr Chem ; 339: 97-143, 2014.
Artigo em Inglês | MEDLINE | ID: mdl-22955503

RESUMO

Organic-aerosol phase partitioning (volatility) and oxidative aging are inextricably linked in the atmosphere because partitioning largely controls the rates and mechanisms of aging reactions as well as the actual amount of organic aerosol. Here we discuss those linkages, describing the basic theory of partitioning thermodynamics as well as the dynamics that may limit the approach to equilibrium under some conditions. We then discuss oxidative aging in three forms: homogeneous gas-phase oxidation, heterogeneous oxidation via uptake of gas-phase oxidants, and aqueous-phase oxidation. We present general scaling arguments to constrain the relative importance of these processes in the atmosphere, compared to each other and compared to the characteristic residence time of particles in the atmosphere.

18.
Environ Sci Technol ; 47(21): 12123-30, 2013.
Artigo em Inglês | MEDLINE | ID: mdl-24107221

RESUMO

Condensation and evaporation modify the properties and effects of atmospheric aerosol particles. We studied the evaporation of aqueous succinic acid and succinic acid/ammonium sulfate droplets to obtain insights on the effect of ammonium sulfate on the gas/particle partitioning of atmospheric organic acids. Droplet evaporation in a laminar flow tube was measured in a Tandem Differential Mobility Analyzer setup. A wide range of droplet compositions was investigated, and for some of the experiments the composition was tracked using an Aerosol Mass Spectrometer. The measured evaporation was compared to model predictions where the ammonium sulfate was assumed not to directly affect succinic acid evaporation. The model captured the evaporation rates for droplets with large organic content but overestimated the droplet size change when the molar concentration of succinic acid was similar to or lower than that of ammonium sulfate, suggesting that ammonium sulfate enhances the partitioning of dicarboxylic acids to aqueous particles more than currently expected from simple mixture thermodynamics. If extrapolated to the real atmosphere, these results imply enhanced partitioning of secondary organic compounds to particulate phase in environments dominated by inorganic aerosol.


Assuntos
Aerossóis/química , Sulfato de Amônio/química , Atmosfera/química , Ácido Succínico/química , Cromatografia Líquida de Alta Pressão/métodos , Ácidos Dicarboxílicos/química , Espectrometria de Massas/instrumentação , Espectrometria de Massas/métodos , Modelos Químicos , Compostos Orgânicos/química , Soluções , Termodinâmica , Volatilização , Água
19.
Nature ; 502(7471): 359-63, 2013 Oct 17.
Artigo em Inglês | MEDLINE | ID: mdl-24097350

RESUMO

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.


Assuntos
Aminas/química , Atmosfera/química , Material Particulado/química , Ácidos Sulfúricos/química , Radiação Cósmica , Dimetilaminas/química , Efeito Estufa , Atividades Humanas , Modelos Químicos , Teoria Quântica , Dióxido de Enxofre/química
20.
Science ; 339(6122): 943-6, 2013 Feb 22.
Artigo em Inglês | MEDLINE | ID: mdl-23430652

RESUMO

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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