Liquid–liquid phase separation in particles containing organics mixed with ammonium sulfate, ammonium bisulfate, ammonium nitrate or sodium chloride

You, Yuan; Renbaum-Wolff, Lindsay; Bertram, Allan K.

doi:10.5194/acp-13-11723-2013

Cited by 121 publications

(241 citation statements)

References 97 publications

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“…Organic aerosol (OA) often dominates over sulfate (Zhang et al, 2007), in particular in the Southeast in summer where there is a large OA source from biogenic hydrocarbons Marais et al, 2016). Mixing of organic and sulfate aerosol may slow down mass transfer due to phase separation, in which the organic aerosol fraction coats the predominantly aqueous inorganic core, as has been observed in many laboratory studies of organic ammonium sulfate particles (Anttila et al, 2007;Ciobanu et al, 2009;Bertram et al, 2011;Koop et al, 2011;You et al, 2013) as well as in the field in the Southeast (You et al, 2012). …”

Section: Introductionmentioning

confidence: 99%

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

et al. 2017

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Abstract. Thermodynamic models predict that sulfate aerosol (S(VI) ≡ H 2 SO 4 (aq) + HSO − 4 + SO 2− 4 ) should take up available ammonia (NH 3 ) quantitatively as ammonium (NH + 4 ) until the ammonium sulfate stoichiometry (NH 4 ) 2 SO 4 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 = [NHshould 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 SO 2 emission controls, the ammonium-sulfate aerosol ratio decreased by 1.4-3.0 % yr −1 . Thus, the aerosol is becoming more acidic even as SO 2 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 SO 2 emissions to decrease sulfate aerosol will not have the co-benefit of suppressing acidcatalyzed secondary organic aerosol (SOA) formation.

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Section: Introductionmentioning

confidence: 99%

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

et al. 2017

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“…This results in a particle whose core is predominantly aqueous and inorganic and whose outer shell is predominantly organic. Partially engulfed morphologies are also possible (Song et al, 2012;Veghte et al, 2013). Therefore, ERH for the phase-separated core of such a particle would be close to the ERH of pure ammonium sulfate (Bertram et al, 2011;Buajarern et al, 2007).…”

Section: A Zawadowicz Et Al: Hygroscopic and Phase Separation Prmentioning

confidence: 99%

“…The evidence for liquid-liquid phase separation comes almost solely from microscopy (Bertram et al, 2011;You et al, 2013;Ciobanu et al, 2009) and EDB studies (Marcolli and Krieger, 2006). As a limit of the resolution, the particles studied are large, on the order of 1 µm diameter or greater (Bertram et al, 2011;Ciobanu et al, 2009;Marcolli and Krieger, 2006).…”

Section: A Zawadowicz Et Al: Hygroscopic and Phase Separation Prmentioning

confidence: 99%

Hygroscopic and phase separation properties of ammonium sulfate/organics/water ternary solutions

et al. 2015

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Abstract. Atmospheric aerosol particles are often partially or completely composed of inorganic salts, such as ammonium sulfate and sodium chloride, and therefore exhibit hygroscopic properties. Many inorganic salts have well-defined deliquescence and efflorescence points at which they take up and lose water, respectively. Field measurements have shown that atmospheric aerosols are not typically pure inorganic salt, instead, they often also contain organic species. There is ample evidence from laboratory studies that suggests that mixed particles exist in a phase-separated state, with an aqueous inorganic core and organic shell. Although phase separation has not been measured in situ, there is no reason it would not also take place in the atmosphere. Here, we investigate the deliquescence and efflorescence points, phase separation and ability to exchange gas-phase components of mixed organic and inorganic aerosol using a flow tube coupled with FTIR (Fourier transform infrared) spectroscopy. Ammonium sulfate aerosol mixed with organic polyols with different O : C ratios, including 1,4-butanediol, glycerol, 1,2,6-hexanetriol, 1,2-hexanediol, and 1,5-pentanediol have been investigated. Those constituents correspond to materials found in the atmosphere in great abundance and, therefore, particles prepared in this study should mimic atmospheric mixed-phase aerosol particles. Some results of this study tend to be in agreement with previous microscopy experiments, but others, such as phase separation properties of 1,2,6-hexanetriol, do not agree with previous work. Because the particles studied in this experiment are of a smaller size than those used in microscopy studies, the discrepancies found could be a size-related effect.

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“…A number of laboratory studies have focused on liquid-liquid phase separations within particles consisting of inorganic and organic fractions (Svenningsson et al, 2006;Carrico et al, 2008;Dusek et al, 2011;Hodas et al, 2015). For example, studies about liquid-liquid separation occurring in mixed organic-inorganic aerosols were performed by Song et al (2012a, b) and You et al (2013) using Raman and optical microscopy, establishing that liquidliquid phase separation typically occurs in mixed organics + ammonium sulfate (AS) particles with an average elemental oxygen-to-carbon (O : C) ratio of the organic fraction of less than 0.6 and in some cases for 0.6 < O : C < 0.8. You et al (2013) further found that for a O : C ratio between 0.5 and 0.8, the occurrence of liquid-liquid phase separation at a moderate to high RH depends on the types of inorganic salts present (i.e., the effective strength of the salting-out effect), e.g., (NH 4 ) 2 SO 4 ≥ NH 4 HSO 4 ≥ NaCl ≥ NH 4 NO 3 .…”

Section: Introductionmentioning

confidence: 99%

“…For example, studies about liquid-liquid separation occurring in mixed organic-inorganic aerosols were performed by Song et al (2012a, b) and You et al (2013) using Raman and optical microscopy, establishing that liquidliquid phase separation typically occurs in mixed organics + ammonium sulfate (AS) particles with an average elemental oxygen-to-carbon (O : C) ratio of the organic fraction of less than 0.6 and in some cases for 0.6 < O : C < 0.8. You et al (2013) further found that for a O : C ratio between 0.5 and 0.8, the occurrence of liquid-liquid phase separation at a moderate to high RH depends on the types of inorganic salts present (i.e., the effective strength of the salting-out effect), e.g., (NH 4 ) 2 SO 4 ≥ NH 4 HSO 4 ≥ NaCl ≥ NH 4 NO 3 . Recently, the effect of a potential size-dependent morphology and dependence of the phase separation mechanism on the organic / inorganic mass ratio in mixed aerosol was studied for mixtures of poly(ethylene glycol)-400 + ammonium sulfate using cryogenic-transmission electron microscopy (Altaf et al, 2016).…”

Section: Introductionmentioning

confidence: 99%

Hygroscopicity of organic surrogate compounds from biomass burning and their effect on the efflorescence of ammonium sulfate in mixed aerosol particles

et al. 2018

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Abstract. Hygroscopic growth factors of organic surrogate compounds representing biomass burning and mixed organic-inorganic aerosol particles exhibit variability during dehydration experiments depending on their chemical composition, which we observed using a hygroscopicity tandem differential mobility analyzer (HTDMA). We observed that levoglucosan and humic acid aerosol particles release water upon dehumidification in the range from 90 to 5 % relative humidity (RH). However, 4-Hydroxybenzoic acid aerosol particles remain in the solid state upon dehumidification and exhibit a small shrinking in size at higher RH compared to the dry size. For example, the measured growth factor of 4-hyroxybenzoic acid aerosol particles is ∼ 0.96 at 90 % RH. The measurements were accompanied by RH-dependent thermodynamic equilibrium calculations using the Aerosol Inorganic-Organic Mixtures Functional groups Activity Coefficients (AIOMFAC) model and Extended Aerosol Inorganics Model (E-AIM), the Zdanovskii-Stokes-Robinson (ZSR) relation, and a fitted hygroscopicity expression. We observed several effects of organic components on the hygroscopicity behavior of mixtures containing ammonium sulfate (AS) in relation to the different mass fractions of organic compounds: (1) a shift of efflorescence relative humidity (ERH) of ammonium sulfate to higher RH due to the presence of 25 wt % levoglucosan in the mixture. (2) There is a distinct efflorescence transition at 25 % RH for mixtures consisting of 25 wt % of 4-hydroxybenzoic acid compared to the ERH at 35 % for organic-free AS particles.(3) There is indication for a liquid-to-solid phase transition of 4-hydroxybenzoic acid in the mixed particles during dehydration. (4) A humic acid component shows no significant effect on the efflorescence of AS in mixed aerosol particles. In addition, consideration of a composition-dependent degree of dissolution of crystallization AS (solid-liquid equilibrium) in the AIOMFAC and E-AIM models leads to a relatively good agreement between models and observed growth factors, as well as ERH of AS in the mixed system. The use of the ZSR relation leads to good agreement with measured diameter growth factors of aerosol particles containing humic acid and ammonium sulfate. Lastly, two distinct mixtures of organic surrogate compounds, including levoglucosan, 4-hydroxybenzoic acid, and humic acid, were used to represent the average water-soluble organic carbon (WSOC) fractions observed during the wet and dry seasons in the central Amazon Basin. A comparison of the organic fraction's hygroscopicity parameter for the simple mixtures, e.g., κ ≈ 0.12 to 0.15 for the wet-season mixture in the 90 to 40 % RH range, shows good agreement with field data for the wet season in the Amazon Basin (WSOC κ ≈ 0.14 ± 0.06 at 90 % RH). This suggests that laboratory-generated mixtures containing organic surrogate compounds and ammonium sulfate can be used to mimic, in a simplified manner, the chemical composition of ambient aerosols from the Amazon Basin for the purpose of RH-de...

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Liquid–liquid phase separation in particles containing organics mixed with ammonium sulfate, ammonium bisulfate, ammonium nitrate or sodium chloride

Cited by 121 publications

References 97 publications

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

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

Hygroscopic and phase separation properties of ammonium sulfate/organics/water ternary solutions

Hygroscopicity of organic surrogate compounds from biomass burning and their effect on the efflorescence of ammonium sulfate in mixed aerosol particles

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