AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
Water-Soluble VOCs and Aerosol CCN Activity: A Tale of Three Surfactants
Neha Sareen, Allison Schwier, Greg Drozd, Joseph Woo, Terry Lathem, Athanasios Nenes, V. FAYE MCNEILL, Columbia University
Abstract Number: 239 Working Group: Aerosols, Clouds, and Climate
Abstract The uptake of water-soluble volatile organic compounds (WSVOCs) by wet atmospheric aerosols can lead to the formation of secondary organic aerosol material (SOA). We have performed a series of laboratory studies in order to quantify of the impact of WSVOC uptake and aqueous-phase SOA formation on aerosol cloud condensation nuclei (CCN) activity. Deliquesced, acidified submicron ammonium sulfate aerosols at >60% RH were exposed to ppb levels of gas-phase methylglyoxal, acetaldehyde, or alpha-pinene oxide (aPO) in a continuous-flow aerosol reaction chamber (residence time = 3-5 h). Aerosol size, composition, and CCN activity was monitored at the reactor outlet via scanning mobility particle sizer (SMPS), continuous-flow streamwise thermal gradient chamber (CFSTGC), and aerosol chemical ionization mass spectrometry (Aerosol-CIMS), respectively.
Methylglyoxal and acetaldehyde are known to form SOA and suppress surface tension in bulk aqueous aerosol mimics, but both of these species have relatively low Henry’s Law constants. We found evidence that adsorption of these species from the gas phase to the gas-aerosol interface significantly impacts aerosol CCN activity, by directly altering the aerosol surface tension. Up to 15% reduction in critical dry diameter for activation was observed without any detectable particle growth due to bulk uptake of organics.
In contrast, aPO is efficiently taken up by the deliquesced aerosols. No detectable change in aerosol CCN activity was apparent at a given dry particle diameter, despite significant aerosol organic content detectable via Aerosol-CIMS and a 20% increase in particle volume. Kohler theory analysis indicates a surface tension of 68 mN/m, commensurate with previous analysis of total WSOC from alpha-pinene. This surface tension depression offsets the expected decrease in hygroscopicity due to the increase in aerosol organic content.
The need for future experiments and modeling studies to further quantify the impacts of WSVOCs on cloud formation and precipitation will be discussed.