AAAR 33rd Annual Conference
October 20 - October 24, 2014
Rosen Shingle Creek
Orlando, Florida, USA
Abstract View
Relating Volatility, Size and Cloud Condensation Nuclei Activation Properties of Longifolene SOA
ASHLEY VIZENOR, Akua Asa-Awuku, University of California, Riverside
Abstract Number: 126 Working Group: Aerosols, Clouds, and Climate
Abstract Longifolene is a sesquiterpene found in pine resin and emitted to the ambient air. Compared to similarly emitted biogenic compounds, it has a longer atmospheric lifetime. This longer lifetime makes it an ideal compound to study in atmospheric chamber experiments as its decay and reactivity can be observed over a greater time with less reactant. Here, longifolene secondary organic aerosol (SOA) was formed upon reaction with hydroxyl radical in dual 90m$^3 Teflon reactors at the University of California, Riverside College of Engineering- Center for Environmental Research and Technology Environmental Chamber. A Volatility Tandem Differential Mobility Analyzer was used during the experiments to observe changes in the volatilities of the SOA formed. Volume Fraction Remaining (VFR) data suggests that upon nucleation, longifolene SOA volatility varies significantly with temperature. The VFR doubles when the thermal denuder temperature is decreased by fifteen degrees Celsius. When reacted with hydroxyl radical, the mode of particles shifts from 50nm to over 200nm within 240 minutes. During this time, the particles begin to decline in volatility, leading to a logarithmic trend between temperature and VFR. The volatility appears to be correlated to particle size, and cloud condensation nuclei (CCN) activation was observed. As the particles grow and their volatility decreases, the supersaturation required for CCN activation decreases from approximately 1% to 0.2%, indicating that the more volatile longifolene SOA species are hygroscopic. These trends were compared to the SOA chemistry of other sesquiterpenes. Furthermore, a lower volatile pre-cursor, isoprene was added to longifolene experiments. Isoprene can produce more volatile products that can influence the overall particle hygroscopcity. The contributions of isoprene and longifolene decay in the gas-phase are observed to determine how the volatility of mixed-phase particles compares with single-phase pre-cursor SOA.