Phase Transitions of Malonic and Oxalic Acid Aerosols

Abstract

Atmospheric aerosol has been shown to contain an organic component that includes a significant fraction of small dicarboxylic acids, particularly in the urban environment. As an initial step toward understanding the phase in which particles may exist, a detailed study into the phase transitions of malonic and oxalic acid aerosols has been carried out. Both the aerosol phase transitions (deliquescence and efflorescence) and bulk solution properties (equilibrium water vapor pressure and the solubility and freezing curves of the aqueous solutions) are reported. An aerosol flow tube-FTIR and a static mode chamber-FTIR have been used to identify particulate phase transitions. In the latter the particles can be observed under ice-supersaturated conditions, allowing investigation of behavior at subeutectic temperatures. We report that both malonic and oxalic acid aerosols sustain a substantial level of solute supersaturation before efflorescence occurs, whereas deliquescence occurs at the thermodynamically predicted relative humidity. At room temperature, malonic acid efflorescence is observed at RH = 6% ± 3% and oxalic acid efflorescence occurs at RH ≤ 5%. Malonic acid particles deliquesce between 69% and 91% RH over the temperature range 293−252 K, and for oxalic acid conditions close to 100% RH are required. We report the first observation of the phase transition of oxalic acid between the anhydrous and dihydrate form and discuss our results in the context of recently published data.

Water Content and Phase Transitions in Particles of Inorganic and Organic Species and their Mixtures Using Micro-Raman Spectroscopy

“…However, formation of AN solids from the initially aqueous particles via heterogeneous nucleation in the presence of sulfate crystals was evident. Peng et al (2001) reported that MA particles did not crystallize at low RH of ∼5%, such crystallization events were observed by Braban et al (2003) at 6% RH. During the growth process, the abrupt increase in both the ν(C=O) peak's position and fwhh at 67% RH indicates deliquescence, consistent with Peng's bulk measurement of 65.3% RH and Braban's determination of 69% RH (Peng et al 2001;Braban et al 2003).…”

“…Peng et al (2001) reported that MA particles did not crystallize at low RH of ∼5%, such crystallization events were observed by Braban et al (2003) at 6% RH. During the growth process, the abrupt increase in both the ν(C=O) peak's position and fwhh at 67% RH indicates deliquescence, consistent with Peng's bulk measurement of 65.3% RH and Braban's determination of 69% RH (Peng et al 2001;Braban et al 2003). For GA, the CRH has been reported as 29-33% (Peng et al 2001) and 22.5-36% (Pant et al 2004).…”

High variability of the heterogeneous ice nucleation potential of oxalic acid dihydrate and sodium oxalate

“…Several recent studies have addressed the hygroscopic behaviour (deliquescence and efflorescence phase transitions) and ice nucleation abilities of low molecular weight dicarboxylic acids (Braban et al, 2003;Kanji et al, 2008;Mikhailov et al, 2009;Parsons et al, 2004;Prenni et al, 2001;Shilling et al, 2006;Treuel et al, 2008;Zobrist et al, 2006). These compounds have been identified as an important contribution to the water-soluble organic fraction of the tropospheric aerosol, typically comprising 1-3% of the total particulate organic carbon in urban and semiurban areas and up to 10% in remote continental and marinecases, oxalic acid (C2) is found to be the most abundant species, followed by malonic (C3) and succinic acid (C4).…”

“…In the following, we will give a brief literature survey on the hygroscopic properties of oxalic acid, starting with the aerosol flow tube/FTIR study by Braban et al (2003). The authors have generated a polydisperse aerosol of anhydrous oxalic acid particles by spray-drying of an aqueous solution at a relative humidity (RH) of less than 5%.…”

A study of the phase transition behavior of internally mixed ammonium sulfate - malonic acid aerosols

“…Several initial studies have focused on the properties of water-soluble organic compounds (WSOC) that are found in the atmosphere. Dicarboxylic acids, which have been identified globally in atmospheric aerosol (Narukawa et al, 1999;Rohrl and Lammel, 2001;Yao et al, 2002;Narukawa et al, 2002), have been considered by several recent phase transition studies (Prenni et al, 2001;Brooks et al, 2002;Braban et al, 2003;Marcolli et al, 2004;Parsons et al, 2004;).…”