Role of nucleation mechanism on the size dependent morphology of organic aerosol

2016 ◽  
Vol 52 (59) ◽  
pp. 9220-9223 ◽  
Author(s):  
Muhammad Bilal Altaf ◽  
Andreas Zuend ◽  
Miriam Arak Freedman
Keyword(s):  
Phase Separation ◽  
Ammonium Sulfate ◽  
Organic Aerosol ◽  
Nucleation And Growth ◽  
Nucleation Mechanism ◽  
Sulfate Aerosol ◽  
Size Dependent ◽  
Peg 400

The size dependent morphology of PEG-400/ammonium sulfate aerosol originates from an activated process during phase separation by nucleation and growth.

scholarly journals The underappreciated role of nonvolatile cations on aerosol ammonium-sulfate molar ratios

2017 ◽  
Author(s):  
Hongyu Guo ◽  
Athanasios Nenes ◽  
Rodney J. Weber
Keyword(s):  
Gas Phase ◽  
Ammonium Sulfate ◽  
Organic Aerosol ◽  
Organic Films ◽  
Organic Film ◽  
Aerosol Chemistry ◽  
Molar Ratios ◽  
Aerosol Acidity ◽  
Aerosol Mass

Abstract. Overprediction of fine particle ammonium-sulfate molar ratios (R) by thermodynamic models is suggested as evidence for an organic film that only inhibits the equilibration of gas phase ammonia (but not water or nitric acid) with aerosol sulfate and questions the equilibrium assumption long thought to apply for submicron aerosol. The ubiquity of such organic films implies significant impacts on aerosol chemistry. We test the organic film hypothesis by analyzing ambient observations with a thermodynamic model and find that R and ammonia partitioning can be accurately reproduced when small amounts of nonvolatile cations (NVC), consistent with observations, are considered in the thermodynamic analysis. Exclusion of NVCs results in predicted R consistently near 2. The error in R is positively correlated with NVC and not organic aerosol mass fraction or concentration. These results strongly challenge the postulated ability of organic films to perturb aerosol acidity or prevent ammonia from achieving gas-particle equilibrium for the conditions considered.

scholarly journals Inconsistency of ammonium–sulfate aerosol ratios with thermodynamic models in the eastern US: a possible role of organic aerosol

2017 ◽  
Vol 17 (8) ◽  
pp. 5107-5118 ◽  
Author(s):  
Rachel F. Silvern ◽  
Daniel J. Jacob ◽  
Patrick S. Kim ◽  
Eloise A. Marais ◽  
Jay R. Turner ◽  
...  
Keyword(s):  
Gas Phase ◽  
Ammonium Sulfate ◽  
Wet Deposition ◽  
Transport Model ◽  
Organic Aerosol ◽  
Sulfate Aerosol ◽  
Chemical Transport Model ◽  
Thermodynamic Models ◽  
So2 Emissions ◽  
Mass Transfer Limitation

Abstract. Thermodynamic models predict that sulfate aerosol (S(VI)  ≡  H2SO4(aq) + HSO4−+ SO42−) should take up available ammonia (NH3) quantitatively as ammonium (NH4+) until the ammonium sulfate stoichiometry (NH4)2SO4 is close to being reached. This uptake of ammonia has important implications for aerosol mass, hygroscopicity, and acidity. When ammonia is in excess, the ammonium–sulfate aerosol ratio R =  [NH4+] ∕ [S(VI)] should approach 2, with excess ammonia remaining in the gas phase. When ammonia is in deficit, it should be fully taken up by the aerosol as ammonium and no significant ammonia should remain in the gas phase. Here we report that sulfate aerosol in the eastern US in summer has a low ammonium–sulfate ratio despite excess ammonia, and we show that this is at odds with thermodynamic models. The ammonium–sulfate ratio averages only 1.04 ± 0.21 mol mol−1 in the Southeast, even though ammonia is in large excess, as shown by the ammonium–sulfate ratio in wet deposition and by the presence of gas-phase ammonia. It further appears that the ammonium–sulfate aerosol ratio is insensitive to the supply of ammonia, remaining low even as the wet deposition ratio exceeds 6 mol mol−1. While the ammonium–sulfate ratio in wet deposition has increased by 5.8 % yr−1 from 2003 to 2013 in the Southeast, consistent with SO2 emission controls, the ammonium–sulfate aerosol ratio decreased by 1.4–3.0 % yr−1. Thus, the aerosol is becoming more acidic even as SO2 emissions decrease and ammonia emissions stay constant; this is incompatible with simple sulfate–ammonium thermodynamics. A tentative explanation is that sulfate particles are increasingly coated by organic material, retarding the uptake of ammonia. Indeed, the ratio of organic aerosol (OA) to sulfate in the Southeast increased from 1.1 to 2.4 g g−1 over the 2003–2013 period as sulfate decreased. We implement a simple kinetic mass transfer limitation for ammonia uptake to sulfate aerosols in the GEOS-Chem chemical transport model and find that we can reproduce both the observed ammonium–sulfate aerosol ratios and the concurrent presence of gas-phase ammonia. If sulfate aerosol becomes more acidic as OA ∕ sulfate ratios increase, then controlling SO2 emissions to decrease sulfate aerosol will not have the co-benefit of suppressing acid-catalyzed secondary organic aerosol (SOA) formation.

scholarly journals The underappreciated role of nonvolatile cations in aerosol ammonium-sulfate molar ratios

2018 ◽  
Vol 18 (23) ◽  
pp. 17307-17323 ◽  
Author(s):  
Hongyu Guo ◽  
Athanasios Nenes ◽  
Rodney J. Weber
Keyword(s):  
Gas Phase ◽  
Ammonium Sulfate ◽  
Fine Particle ◽  
Organic Aerosol ◽  
Molar Ratio ◽  
Strongly Correlated ◽  
Ammonia Gas ◽  
Molar Ratios ◽  
Aerosol Acidity

Abstract. Overprediction of fine-particle ammonium-sulfate molar ratios (R) by thermodynamic models is suggested as evidence for interactions with organic constituents that inhibit the equilibration of gas-phase ammonia with aerosol sulfate and questions the equilibrium assumption long thought to apply for submicron aerosol. This hypothesis is tested through thermodynamic analysis of ambient observations. We find that the deviation between R from a molar ratio of 2 is strongly correlated with the concentration of sodium (Na+), a nonvolatile cation (NVC), but exhibits no correlation to organic aerosol (OA) mass concentration or mass fraction. Thermodynamic predictions of both R and ammonia gas–particle partitioning can accurately reproduce observations when small amounts of NVCs are included in the calculations, whereas exclusion of NVCs results in a predicted R consistently near 2. The sensitivity of R to small amounts of NVCs arises because, when the latter are present but not included in the thermodynamic calculations, the missing cations are replaced with ammonium in the model (NH3–NH4+ equilibrium shifts to the particle), resulting in an R that is biased high. Results and conclusions based on bulk aerosol considerations that assume all species are internally mixed are not changed even if NVCs and sulfate are largely externally mixed; fine-particle pH is found to be much less sensitive to mixing state assumptions than molar ratios. We also show that the data used to support the “organic inhibition” of NH3 from equilibrium, when compared against other network and field campaign datasets, display a systematically and significantly lower NH4+ (thought to be from an evaporation bias), that is of the order of the effect postulated to be caused by organics. Altogether, these results question the postulated ability of organic compounds to considerably perturb aerosol acidity and prevent ammonia from achieving gas–particle equilibrium, at least for the locations considered. Furthermore, the results demonstrate the limitations of using molar ratios to infer aerosol properties or processes that depend on particle pH.

scholarly journals Liquid–liquid phase separation and morphologies in organic particles consisting of <i>α</i>-pinene and <i>β</i>-caryophyllene ozonolysis products and mixtures with commercially available organic compounds

2020 ◽  
Vol 20 (19) ◽  
pp. 11263-11273
Author(s):  
Young-Chul Song ◽  
Ariana G. Bé ◽  
Scot T. Martin ◽  
Franz M. Geiger ◽  
Allan K. Bertram ◽  
...  
Keyword(s):  
Phase Separation ◽  
Liquid Phase ◽  
Aerosol Particles ◽  
Organic Aerosol ◽  
Nucleation And Growth ◽  
Liquid Phases ◽  
Two Component ◽  
Organic Particles ◽  
Nucleation And Growth Mechanism ◽  
Liquid Liquid Phase Separation

Abstract. Liquid–liquid phase separation (LLPS) in organic aerosol particles can impact several properties of atmospheric particulate matter, such as cloud condensation nuclei (CCN) properties, optical properties, and gas-to-particle partitioning. Yet, our understanding of LLPS in organic aerosols is far from complete. Here, we report on the LLPS of one-component and two-component organic particles consisting of α-pinene- and β-caryophyllene-derived ozonolysis products and commercially available organic compounds of relevance to atmospheric organic particles. In the experiments involving single-component organic particles, LLPS was observed in 8 out of 11 particle types studied. LLPS almost always occurred when the oxygen-to-carbon elemental ratio (O:C) was ≤0.44 but did not occur when O:C was >0.44. The phase separation occurred by spinodal decomposition as well as the nucleation and growth mechanism, and when LLPS occurred, two liquid phases coexisted up to ∼100 % relative humidity (RH). In the experiments involving two-component organic particles, LLPS was observed in 23 out of 25 particles types studied. LLPS almost always occurred when the average was O:C ≤0.67 but never occurred when the average O:C was >0.67. The phase separation occurred by spinodal decomposition as well as the nucleation and growth mechanism. When LLPS occurred, two liquid phases coexisted up to ∼100 % RH. These results provide further evidence that LLPS is likely a frequent occurrence in organic aerosol particles in the troposphere, even in the absence of inorganic salts.

Modelling hygroscopicity-induced gas–aerosol partitioning, organic surface enrichment and cloud droplet formation

2020 ◽  
Author(s):  
Andreas Zuend ◽  
Kyle Gorkowski
Keyword(s):  
Surface Tension ◽  
Phase Separation ◽  
Cloud Droplet ◽  
Organic Aerosol ◽  
Chem Phys ◽  
Computationally Efficient ◽  
Volatile Organic ◽  
Reduced Complexity ◽  
Droplet Activation

&lt;p&gt;The interactions among low and semi-volatile organic compounds, water and other inorganic components within fine-mode aerosols are complex. We show that understanding several features of this complexity can be important in the context of phase separation, a particle surface composition enriched by organics and for related cloud droplet activation modeling. &amp;#160;&lt;br&gt;Context: oxidized organic compounds contribute to the particle hygroscopicity, yet typically to a lesser extent than dissolved inorganic ions. The overall hygroscopicity of aerosols in turn greatly affects their water uptake in an air parcel experiencing increasing relative humidity. The mechanism acts directly in terms of adding water mass, as well as indirectly via a hygroscopicity-induced feedback leading to enhanced gas&amp;#8211;to&amp;#8211;particle partitioning of semi-volatile organic components alongside a re-equilibration of the aerosol with inorganic acids, ammonia and further water uptake. Furthermore, non-ideal mixing may induce liquid&amp;#8211;liquid phase separation, often leading to an organic-rich phase of relatively low surface tension surrounding an inorganic-rich particle core. This phase separation effect and related surface enhancements of organic component concentrations affect not only the morphology but also the potential for near-surface chemical reactions, as well as the thermodynamics controlling an aerosol particle&amp;#8217;s activation into a cloud droplet at realistic water vapour supersaturations. &amp;#160;New experimental techniques and field observations over the past few years have encouraged model development for an improved representation of these processes on a detailed level (see, e.g., discussion in Davies et al., 2019). This has led to a better understanding of the potential role of organic aerosol compounds spanning a range of polarities and an associated evolution of surface tension prior to the cloud condensation nucleus (CCN) activation point. While detailed process models still lack finer details to fully capture these composition and phase effects reliably and predictively, important challenges exist in translating these mechanisms into computationally efficient and feasible reduced-complexity models of use for air quality and chemistry-climate modelling.&lt;br&gt;In this presentation, we will outline the current state of a relatively complete process-level aerosol thermodynamics model based on AIOMFAC and introduce key features of a recently developed reduced-complexity organic aerosol model that accounts for water content and hygroscopicity-induced feedbacks on composition (Gorkowski et al., 2019). A key advantage of the reduced-complexity model is its ability to use only input typically known from field measurements or data available in large-scale air quality models. Our approach is compatible with a volatility basis set approach and allows for extending it by adding a realistic humidity dependence. In addition, we account for phase separation and related effects on surface tension in a simplified, computationally efficient manner. This approach and its results for aerosol hygroscopicity and cloud droplet activation will be discussed.&lt;/p&gt;&lt;p&gt;References:&lt;/p&gt;&lt;p&gt;Davies, J. F., Zuend, A., and Wilson, K. R.: Technical note: The role of evolving surface tension in the formation of cloud droplets, Atmos. Chem. Phys., 19, 2933&amp;#8211;2946, doi:10.5194/acp-19-2933-2019, 2019.&lt;/p&gt;&lt;p&gt;Gorkowski, K., Preston, T. C., and Zuend, A.: Relative-humidity-dependent organic aerosol thermodynamics via an efficient reduced-complexity model, Atmos. Chem. Phys., 19, 13383&amp;#8211;13407, 10.5194/acp-19-13383-2019, 2019.&lt;/p&gt;

Key Role of the Oxidized Citrate-Free Radical in the Nucleation Mechanism of the Metal Nanoparticle Turkevich Synthesis

2019 ◽  
Vol 123 (36) ◽  
pp. 22624-22633 ◽  
Author(s):  
Sarah Al Gharib ◽  
Jean-Louis Marignier ◽  
Abdel Karim El Omar ◽  
Adnan Naja ◽  
Sophie Le Caer ◽  
...  
Keyword(s):  
Free Radical ◽  
Nucleation Mechanism ◽  
Metal Nanoparticle

The role of rough surface in the size-dependent behavior upon nano-indentation

2021 ◽  
pp. 103836
Author(s):  
Ding Tang ◽  
Leilei Zhao ◽  
Huamiao Wang ◽  
Dayong Li ◽  
Yinghong Peng ◽  
...  
Keyword(s):  
Rough Surface ◽  
Nano Indentation ◽  
Size Dependent ◽  
Dependent Behavior
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