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RESEARCH ARTICLE
Contents Vol 6(5)

Water uptake of humic and fulvic acid: measurements and modelling using single parameter Köhler theory

Courtney D. Hatch A B C , Kelly M. Gierlus A , James Zahardis A , Jennifer Schuttlefield A and Vicki H. Grassian A B D
+ Author Affiliations
- Author Affiliations

A Department of Chemistry, University of Iowa, Iowa City, IA 52242, USA.

B Center for Global and Regional Environmental Research, University of Iowa, Iowa City, IA 52242, USA.

C Present address: Hendrix College, 1600 Washington Ave., Conway, AR 72032, USA. Email: hatch@hendrix.edu

D Corresponding author. Email: Vicki-Grassian@uiowa.edu

Environmental Chemistry 6(5) 380-388 https://doi.org/10.1071/EN09083
Submitted: 3 July 2009  Accepted: 16 September 2009   Published: 22 October 2009

Environmental context. Humic and fulvic acids are macromolecular, multifunctional, polyacidic compounds that are important proxies for humic-like substances (HULIS), which are ubiquitous components of tropospheric particulate matter. The hygroscopic nature of these substances suggests that they can contribute to direct and indirect climate forcing. Thus, the effects of water uptake in humic-like particles in the atmosphere must be well understood.

Abstract. The water uptake of humic and fulvic acid aerosols was determined by hygroscopic tandem differential mobility analysis (hTDMA) and extinction Fourier transform infrared (FTIR) spectroscopy. Water uptake on humic and fulvic acid thin films was also investigated using attenuated total reflectance (ATR) FTIR spectroscopy. The hygroscopic growth of monodisperse, 100-nm (dry) Suwannee River fulvic acid (SRFA) and humic acid sodium salt (NaHA) aerosols was determined and modelled using Köhler theory. A single parameter, the ionic density (ρion), which contains physical properties that are not well established for these substances, was determined for SRFA and NaHA to be 2.1 × 10–3 and 7.0 × 10–3 mol cm–3 respectively. The hygroscopic growth was then modelled using the ρion-Köhler equation and the critical parameters determined. The critical percent supersaturation of SRFA and NaHA was determined to be 0.60 and 0.33% respectively using the surface tension of water; and 0.35 and 0.19% respectively using the surface tension of aqueous HULIS. κ-Köhler theory, was also used to calculate the critical supersaturation and was found to be in good agreement with the ρion representation. Both extinction FTIR of aerosols and ATR-FTIR absorption measurements of thin films confirm enhanced water uptake with increasing relative humidity (RH).

Additional keywords: HULIS, hygroscopic growth.


Acknowledgements

This work was supported by the National Science Foundation under grants CHE0503854 and ATM0613124. Any opinions, findings and conclusions or recommendations expressed in this material are those of the authors and do not reflect the views of the National Science Foundation. C.D.H. also received funding from the University of Iowa Cardiovascular Center Institutional Research Fellowship.


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