Hygroscopicity of organic compounds from biomass burning and their influence on the water uptake of mixed organic ammonium sulfate aerosols

Abstract

Abstract. Hygroscopic behavior of organic compounds, including levoglucosan, 4-hydroxybenzoic acid, and humic acid, as well as their effects on the hygroscopic properties of ammonium sulfate (AS) in internally mixed particles are studied by a hygroscopicity tandem differential mobility analyzer (HTDMA). The organic compounds used represent pyrolysis products of wood that are emitted from biomass burning sources. It is found that humic acid aerosol particles only slightly take up water, starting at RH (relative humidity) above ∼ 70 %. This is contrasted by the continuous water absorption of levoglucosan aerosol particles in the range 5-90 % RH. However, no hygroscopic growth is observed for 4-hydroxybenzoic acid aerosol particles. Predicted water uptake using the ideal solution theory, the AIOMFAC model and the E-AIM (with UNIFAC) model are consistent with measured hygroscopic growth factors of levoglucosan. However, the use of these models without consideration of crystalline organic phases is not appropriate to describe the hygroscopicity of organics that do not exhibit continuous water uptake, such as 4-hydroxybenzoic acid and humic acid. Mixed aerosol particles consisting of ammonium sulfate and levoglucosan, 4-hydroxybenzoic acid, or humic acid with different organic mass fractions, take up a reduced amount of water above 80 % RH (above AS deliquescence) relative to pure ammonium sulfate aerosol particles of the same mass. Hygroscopic growth of mixtures of ammonium sulfate and levoglucosan with different organic mass fractions agree well with the predictions of the thermodynamic models. Use of the Zdanovskii-Stokes-Robinson (ZSR) relation and AIOMFAC model lead to good agreement with measured growth factors of mixtures of ammonium sulfate with 4-hydroxybenzoic acid assuming an insoluble organic phase. Deviations of model predictions from the HTDMA measurement are mainly due to the occurrence of a microscopical solid phase restructuring at increased humidity (morphology effects), which are not considered in the models. Hygroscopic growth factors of mixed particles containing humic acid are well reproduced by the ZSR relation. Lastly, the organic surrogate compounds represent a selection of some of the most abundant pyrolysis products of biomass burning. The hygroscopic growths of mixtures of the organic surrogate compounds with ammonium sulfate with increasing organics mass fraction representing ambient conditions from the wet to the dry seasonal period in the Amazon basin, exhibit significant water uptake prior to the deliquescence of ammonium sulfate. The measured water absorptions of mixtures of several organic surrogate compounds (including levoglucosan) with ammonium sulfate are close to those of binary mixtures of levoglucosan with ammonium sulfate, indicating that levoglucosan constitutes a major contribution to the aerosol water uptake prior to (and beyond) the deliquescence of ammonium sulfate. Hence, certain hygroscopic organic surrogate compounds can substantially affect the deliquescence point of ...

Surface tension prevails over solute effect in organic-influenced cloud droplet activation

“…We use a state-of-the-art thermodynamic equilibrium model to compute (see Section 3.2). The particle diameter D is calculated by assuming linear additivity of the partial volume contributions by the mixture species based on their densities, as done in prior work 53,60 . Estimated pure-component densities for the surrogate systems studied in this work are listed in Tables S3.1 and S3.2.…”

Influence of particle-phase state on the hygroscopic behavior of mixed organic–inorganic aerosols

“…Multiple studies have sought to elucidate the hygroscopic properties of OA, as well as the influence of organic aerosol components on the hygroscopic behavior and phase transitions of inorganic salts. Much of this work has focused on single-and multicomponent aerosols comprised of carboxylic, dicarboxylic, and humic acids (e.g., Prenni et al, 2001;Choi and Chan, 2002a;Brooks et al, 2004;Chan et al, 2006;Moore and Raymond, 2008;Hatch et al, 2009;Pope et al, 2010;Lei et al, 2014), as well as mixtures of organic acids with inorganic salts (e.g., Cruz and Pandis, 2000;Choi and Chan, 2002b;Prenni et al, 2003;Wise et al, 2003;Brooks et al, 2004;Svenningsson et al, 2006;Sjogren et al, 2007;Gao et al, 2008). Recent studies have explored water uptake by sugars, higher molecular weight organics, and polymers (Gysel et al, 2004;Mochida and Kawamura, 2004;Tong et al, 2011;Zobrist et al, 2011;Lei et al, 2014;Xu et al, 2014).…”

Investigation of water adsorption and hygroscopicity of atmospherically relevant particles using a commercial vapor sorption analyzer

“…These techniques have been summarized and discussed by a very recent review paper (Tang et al, 2016), and here we only mention widely used ones. For airborne monodisperse particles typically produced by a differential mobility analyzer (DMA), the hygroscopicity can be determined by measuring their diameters at dry (typically at RH < 15 % or lower) and humidified conditions (Swietlicki et al, 2008;Freedman et al, 2009;Robinson et al, 2013;Lei et al, 2014). Typically, the diameter change is determined by using a scanning particle mobility sizer (in which mobility diameters are measured) (Vlasenko et al, 2005;Swietlicki et al, 2008;Herich et al, 2009;Koehler et al, 2009;Wu et al, 2011) or aerosol extinction cavity ring-down spectrometry (in which optical diameters are measured) (Freedman et al, 2009;Attwood and Greenslade, 2011).…”

“…Detailed descriptions of the E-AIM model can be found elsewhere (Clegg et al, 1998;Friese and Ebel, 2010). Hygroscopic growth factors, calculated using the E-AIM model, have been widely used to compare with experimental measurements to verify the performance of a variety of instruments, techniques, and/or methods developed for hygroscopic growth studies Lei et al, 2014;Estillore et al, 2016). We show that this instrument can measure a relative mass change (due to water uptake) of < 0.025 % within 6 h and < 0.05 % within 24 h, and the accuracy of mass change measurement is mainly limited by baseline drifts.…”