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

Abstract

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...

Effect of mixing structure on the water uptake of mixtures of ammonium sulfate and phthalic acid particles

“…However, the discrepancy between measured growth factor of well-mixed AS/PA particles at 75 % RH and the predicted growth factors by using the ZSR relation may be due to the molecule interaction between organic molecular and completely or partially dissolved AS ions. A similar phenomenon was reported for well-mixed mixtures of AS + levoglucosan in the previous study by Lei et al (2014Lei et al ( , 2018. Figure 3 shows the measured hygroscopic growth of core-shell structured particles as a function of RH.…”

“…The ability of aerosol particles to absorb and maintain water molecules, called hygroscopicity, is one of the most important physico-chemical properties of atmospheric aerosol particles with profound implications (Shi et al, 2012;Lei et al, 2014Lei et al, , 2018Gupta et al, 2015;Hodas et al, et al, 2015;Zawadowicz et al, 2015;Martin et al, 2017). It might determine the phase state (Mu et al, 2018), size (Peng et al, 2001;Choi et al, 2002), mixing state, optical properties, and chemical reactivity of atmospheric aerosols exposed to the environment of the different relative humidities https://doi.org/10.5194/acp-2020-632 Preprint.…”

Effect of mixing structure on the water uptake of mixtures of ammonium sulfate and phthalic acid particles

“…Atmospheric aerosols contain a complex mixture of inorganic and organic compounds in different mixing structures, e.g., externally mixed or internally mixed (Ganguly et al, 2006). The internally well-mixed aerosol particles may be divided into homogeneous and heterogeneous internally mixed aerosol particles (Lang-Yona et al, 2010), which could, in turn, strongly influence the water uptake, optical properties, and cloud condensation nuclei (CCN) ability of the particles (Lesins et al, 2002;Falkovich et al, 2004;Zhang et al, 2005;Schwarz et al, 2006;Su et al, 2010). Most of the previous studies on the hygroscopic behavior of multicomponent aerosols focus on the well-mixed particles generated from internally mixed solutions (Miñambres et al, 2010;Shi et al, 2012;Gupta et al, 2015;Jing et al, 2016;Lei et al, 2014Lei et al, , 2018.…”

Nano-hygroscopicity tandem differential mobility analyzer (nano-HTDMA) for investigating hygroscopic properties of sub-10 nm aerosol nanoparticles

“…T. Lei et al: Nano-HTDMA for investigating hygroscopic properties of nanoparticles ficiently act as cloud condensation nuclei and, thus, to change the contributions of aerosol nanoparticles to climate forcing (Lihavainen, 2003;Wiedensohler et al, 2009;Sihto et al, 2011;Kirkby et al, 2011;Keskinen et al, 2013;Dunne et al, 2016;Kim et al, 2016). These processes strongly depend on the chemical composition and physicochemical properties of these nanoparticles (Köhler, 1936;Su et al, 2010;Wang et al, 2015;Cheng et al, 2015).…”