Abstract
Abstract. Accurate estimates of particle surface tension are required for models concerning atmospheric aerosol nucleation and activation. However, it is difficult to collect the volumes of atmospheric aerosol required by typical instruments that measure surface tension, such as goniometers or Wilhelmy plates. In this work, a method that measures, ex situ, the surface tension of collected liquid nanoparticles using atomic force microscopy is presented. A film of particles is collected via impaction and is probed using nanoneedle tips with the atomic force microscope. This micro-Wilhelmy method allows for direct measurements of the surface tension of small amounts of sample. This method was verified using liquids, whose surface tensions were known. Particles of ozone oxidized α-pinene, a well-characterized system, were then produced, collected, and analyzed using this method to demonstrate its applicability for liquid aerosol samples. It was determined that oxidized α-pinene particles formed in dry conditions have a surface tension similar to that of pure α-pinene, and oxidized α-pinene particles formed in more humid conditions have a surface tension that is significantly higher.
Highlights
According to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change, clouds and aerosols contribute the largest uncertainty to understanding changes in climate (Boucher et al, 2013)
A major difficulty in modeling particle nucleation and aerosol activation lies in determining physical properties of particles on the nanoscale without precise knowledge about chemical composition
Our results suggest that the surface tension of dry, oxidized α-pinene particles is not very different from the surface tension of its volatile organic compound (VOC) precursor
Summary
According to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change, clouds and aerosols contribute the largest uncertainty to understanding changes in climate (Boucher et al, 2013). Recent studies in particle nucleation and cloud droplet activation have used various methods to estimate particle surface tension, which is a very important parameter in modeling both processes (Duplissy et al, 2008; Kiss et al, 2005; Laaksonen and McGraw, 1996; Moldanova and Ljungström, 2000; Petters et al, 2009; Prisle et al, 2010; Sorjamaa et al, 2004; Wex et al, 2009). A direct method of measuring the surface tensions of particles immediately after nucleation is preferable to these assumptions and would likely reduce the error in particle nucleation models
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