AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
Abstract View
Influence of Ammonia and Relative Humidity on the Optical Properties of Secondary Organic Aerosol Particles
YUMENG CUI, Alexander Frie, Isis Frausto-Vicencio, Francesca Hopkins, Roya Bahreini, University of California, Riverside
Abstract Number: 590 Working Group: Carbonaceous Aerosol
Abstract To understand the radiative impacts of secondary organic aerosol (SOA) particles, it is important to know their optical properties. In this work, we investigate the impact of ammonia (NH3) at different relative humidity (RH) levels on SOA optical properties. For this investigation, SOA was produced by reacting 1-methylnaphthalene or longifolene, with hydroxyl radicals under variable nitric oxide, RH, and NH3 conditions. During SOA formation, the chemical composition and optical properties of SOA were monitored. In addition, single scattering albedo (SSA), mass absorption coefficient (MAC), and refractive index (RI) of SOA at λ=375 nm were calculated.
At low RH (< ~30%) and in the presence of NH3, longifolene SOA had relatively high SSA values and low absorption coefficients (βabs) under both intermediate- and high-NOx regimes. This suggests that longifolene SOA is mostly scattering. In 1-methylnaphthalene experiments, βabs increased soon after initiation of the experiment, and the resulting SSA and MAC values suggest the formation of light-absorbing aerosols (with MACmax≈0.3-0.4 m2/g). The chemical composition of SOA will be analyzed, and results about the organic and nitrate fraction in aerosols along with the contribution of organic nitrates will be related to the SOA optical properties. To better understand the role of NH3 under different conditions, results from experiments at higher RH (60%-70%) will also be provided.