Articles | Volume 17, issue 4
Research article
20 Feb 2017
Research article |  | 20 Feb 2017

Hygroscopic growth of water soluble organic carbon isolated from atmospheric aerosol collected at US national parks and Storm Peak Laboratory

Nathan F. Taylor, Don R. Collins, Douglas H. Lowenthal, Ian B. McCubbin, A. Gannet Hallar, Vera Samburova, Barbara Zielinska, Naresh Kumar, and Lynn R. Mazzoleni

Abstract. Due to the atmospheric abundance and chemical complexity of water soluble organic carbon (WSOC), its contribution to the hydration behavior of atmospheric aerosol is both significant and difficult to assess. For the present study, the hygroscopicity and CCN activity of isolated atmospheric WSOC particulate matter was measured without the compounding effects of common, soluble inorganic aerosol constituents. WSOC was extracted with high purity water from daily high-volume PM2.5 filter samples and separated from water soluble inorganic constituents using solid-phase extraction. The WSOC filter extracts were concentrated and combined to provide sufficient mass for continuous generation of the WSOC-only aerosol over the combined measurement time of the tandem differential mobility analyzer and coupled scanning mobility particle sizer–CCN counter used for the analysis. Aerosol samples were taken at Great Smoky Mountains National Park during the summer of 2006 and fall–winter of 2007–2008; Mount Rainier National Park during the summer of 2009; Storm Peak Laboratory (SPL) near Steamboat Springs, Colorado, during the summer of 2010; and Acadia National Park during the summer of 2011. Across all sampling locations and seasons, the hygroscopic growth of WSOC samples at 90 % RH, expressed in terms of the hygroscopicity parameter, κ, ranged from 0.05 to 0.15. Comparisons between the hygroscopicity of WSOC and that of samples containing all soluble materials extracted from the filters implied a significant modification of the hydration behavior of inorganic components, including decreased hysteresis separating efflorescence and deliquescence and enhanced water uptake between 30 and 70 % RH.

Short summary
The impacts of aerosols on health, visibility, and climate are very sensitive to their ability to take up water under subsaturated conditions and to serve as cloud condensation nuclei. These hydration properties are tightly linked to aerosol composition. This report finds that water soluble organic compounds contribute significantly to atmospheric aerosol hydration both as an independent fraction of aerosol mass and through complementary interactions with common inorganic aerosol constituents.
Final-revised paper