Hygroscopic growth of common organic aerosol solutes, including humic substances, as derived from water activity measurements

Abstract

[1] Studies have shown that organic matter often constitutes up to 50% by mass of tropospheric aerosols. These organics may considerably affect the water uptake properties of these aerosols, impacting Earth's climate and atmosphere. However, considerable uncertainties still exist about hygroscopic properties of organic carbon (OC) in particles. In this study, we have assembled an apparatus to measure equilibrium water vapor pressure over bulk solutions. We used these results to calculate the hygroscopic growth curve and deliquescence relative humidity (DRH) of representative compounds in three OC categories: saccharides, mono/dicarboxylic acids, and HULIS (Humic-Like Substances). To our knowledge, this is the first study to examine the hygroscopic growth of HULIS by means of a bulk method on representative compounds such as fulvic and humic acids. We also explored the temperature effect on hygroscopic growth within the 0°C-30°C temperature range and found no effect. The DRH and hygroscopic growth obtained were in excellent agreement with published tandem differential mobility analyzer (TDMA), electrodynamic balance, and bulk data for sodium chloride, ammonium sulfate, d-glucose, levoglucosan, succinic acid, and glutaric acid. However, we found a hygroscopic growth factor of 1.0 at a relative humidity of 90% for phthalic, oxalic, humic, and two fulvic acids; these results disagree with various TDMA studies. The TDMA is used widely to study water uptake of organic particles but can be affected by particle microstructural arrangements before the DRH and by the inability to fully dry particles. Thus, in the future it will be important to confirm TDMA data for nondeliquescent organic particles with alternate methods.Citation: Zamora, I. R., A. Tabazadeh, D. M. Golden, and M. Z. Jacobson (2011), Hygroscopic growth of common organic aerosol solutes, including humic substances, as derived from water activity measurements,

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

“…For example, the measured diameter growth factors of levoglucosan particles at 80, 60, and 30 % RH are 1.19, 1.09, and 1.03, respectively, which are similar to results obtained for the hydration process of such particles. Levoglucosan has a DRH of ∼ 80 to 83 % (for a bulk system) at 293 to 298 K (Mochida and Kawamura, 2004;Zamora et al, 2011). The similarity of diameter growth factors both under hydration and dehydration conditions even below the DRH of levoglucosan is explained by the lack of crystallization of levoglucosan upon drying to low RH and the presence of a metastable supersaturated aqueous levoglucosan solution in both the hydration and dehydration modes for experiments initiated with liquid solution droplets (Mochida and Kawamura, 2004;Svenningsson et al, 2006).…”

Measuring and modeling the hygroscopic growth of two humic substances in mixed aerosol particles of atmospheric relevance

“…The equilibrium water vapor pressure was measured as a function of temperature and solution concentration with a water activity apparatus. This study builds upon our previous work quantifying the hygroscopic growth of single organic solutes (Zamora et al, 2011).…”

“…This uncertainty range was found over a relative humidity range of 70-99.9 %. Full details of our method calibration, validation and quality control experiments can be found in Zamora et al, 2011. This study employed a thermocouple with higher accuracy; thus the measurement uncertainty for the mixtures is lower than for the pure substances. This uncertainty was based on the accuracy of the thermocouple, and on the precision obtained experimentally for the vapor pressure measurements.…”

“…Water vapor pressure measurements were conducted with a bulk method described in detail by Zamora et al (2011). Briefly, the apparatus used consists of a removable glass sample vessel, mechanically pumped glass lines wrapped with heating tape, a temperature-controlled bath, and a 100 torr Baratron capacitance manometer (Model 626A12TBE, MKS Instruments, Andover, MA).…”

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

“…2013). Water-soluble organic carbon is also linked to a class of complex poly carboxylic acids, which are denoted by the generic term "HULIS" (humic-like substances) (Decesari et al, 2001;Fuzzi et al, 2001;Dinar et al, 2006aDinar et al, , b, 2007Pope et al, 2010;Fors et al, 2010;Zamora et al, 2011). Also, an aerosol population can appear as externally mixed, heterogeneously internally mixed (i.e., coated or phase-separated particles) or homogeneously internally mixed (Riziq et al, 2008;Shamjad et al, 2012;Maskey et al, 2014).…”