AAAR 35th Annual Conference October 17 - October 21, 2016 Oregon Convention Center Portland, Oregon, USA
Abstract View
Gas Phase Vapors Play a Critical Role in Cloud Condensation Nuclei Activation
ASHLEY VIZENOR, Akua Asa-Awuku, University of California, Riverside
Abstract Number: 114 Working Group: Aerosols, Clouds, and Climate
Abstract Particles that can uptake water and form cloud droplets are referred to as cloud condensation nuclei (CCN). The hygroscopicity, or ability of a particle to activate is traditionally quantified by a single parameter, kappa. Traditional CCN analysis is performed by dividing the number of particles activated by the total number of particles (condensation nuclei, CN). The point at which the ratio equals 0.5 is used to identify the critical supersaturation at which 50% of the particles activate for a given diameter. Alternatively, the critical diameter at which 50% of particles for a given supersaturation can be identified. This critical supersaturation and the corresponding dry diameter are then used to calculate kappa-hygroscopicity. However, this calculation assumes that the hygroscopicity of particles stays constant for a given precursor gas.
In the experiments presented, the CCN activity of secondary organic aerosol (SOA) from the photooxidation of two biogenic compounds, isoprene and longifolene were studied. Experiments were carried out in the UCR CE-CERT Environmental Chamber. A TSI SMPS ran in parallel with a Droplet Measurement Technologies Cloud Condensation Nuclei Counter (CCNC) was used to observe the hygroscopicity of resulting SOA, and an Agilent GC-FID quantified the gas-phase decay of the precursors. The gas phase decay of precursors was then related to the CCN/CN ratio rather than the size distribution to test if gas phase precursors play a direct role in CCN activation, and the extent to which the precursors influence CCN activation.