AAAR 35th Annual Conference October 17 - October 21, 2016 Oregon Convention Center Portland, Oregon, USA
Abstract View
Hygroscopicity of Sub 30nm SOA Particles during CLOUD 10
ANGELA BUCHHOLZ, Pasi Miettinen, Aki Pajunoja, Olli Väisänen, Hao Wang, Arttu Ylisirniö, Annele Virtanen, University of Eastern Finland
Abstract Number: 336 Working Group: Aerosols, Clouds, and Climate
Abstract The impact of aerosol particles on the atmosphere depends strongly on their ability to take up water vapor (hygroscopicity) and act as cloud condensation nuclei. The hygroscopicity is determined by the composition and the size of the particles.
Sulfuric acid (H$_2SO$_4), ammonia and oxidized organic vapors play an important role in new particle formation of secondary organic aerosol (SOA) and growth of those particles. The CLOUD chamber at CERN was designed to study new particle formation and the early stages of particle growth. During the CLOUD10 campaign a range of different conditions (e.g. organic precursors, oxidation conditions) was studied aiming at mimicking atmospheric relevant processes as well as possible and at the same time deciphering the influence of the different factors on hygroscopicity.
The hygroscopic growth factor at 90% relative humidity was measured with a custom built Hygroscopicity Tandem Differential Mobility Analyzer (nanoHTDMA) for particles of sizes from 10 to 25nm, and the hygroscopicity parameter kappa was calculated based on Petters and Kreidenweis (2007). As the kappa values for pure H$_2SO$_4 and alpha-pinene derived SOA are known, the volume fractions of organics and H$_2SO$_4 in the particles can be calculated with the simple Zdanovskii–Stokes–Robinson mixing rule. Direct measurements of the chemical composition of sub 30 nm particles is quite challenging. Thus, size resolved hygroscopicity measurements may give valuable insides into the composition of these particles.
Higher gas phase H$_2SO$_4 concentrations increased the hygroscopicity of the particles while higher organic precursor concentrations in the gas phase decreased it. Only a small effect of the particle size was observed between 15 and 25nm. The impact of NOx in the system was also investigated. NO$_x can influence the composition of the particles directly through the oxidation pathway of the organics and indirectly by changing the H$_2SO$_4 concentration in the chamber.