Connecting the Physicochemical Properties with Cloud Condensation and Ice Nucleation Activities of Secondary Organic Aerosol (SOA) Formed through Multiphase Chemical Reactions
SINING NIU, Janie (Yeaseul) Kim, Christopher Rapp, Miska Olin, Zezhen Cheng, Xiaoli Shen, Gregory W. Vandergrift, Yuzhi Chen, Claire E. Moffett, Gourihar Kulkarni, Alla Zelenyuk, Swarup China, Jason Surratt, Daniel Cziczo, Yue Zhang, Texas A&M University
Abstract Number: 386
Working Group: Aerosol Chemistry
Abstract
Current knowledge regarding the climate impact of secondary organic aerosol (SOA) are still not well understood. A primary reason is the limited knowledge of SOA serving as cloud condensation nuclei or ice nucleation particles due to their complex physicochemical properties and formation mechanism.
Here, we conducted chamber experiments with multiphase reactions of SOA generation from oxidation products of biogenic volatile organic compounds with neutral (ammonium sulfate) and acidic (ammonium bisulfate) seeds. We investigated the impact of seed acidity and physicochemical properties of SOA on their cloud formation.
The concentration and chemical composition of the SOA were determined by a High-Resolution Aerosol Mass Spectrometer (HR-AMS) and a Nanospray Desorption Electrospray Ionization (nano-DESI) coupled with an Orbitrap mass spectrometer. The morphology and phase state of SOAs were analyzed with a Scanning Electron Microscope (SEM). The miniaturized version of the Single Particle Laser-Ablation Time-of-Flight mass spectrometer (miniSPLAT) coupled with an evaporation chamber provided the volatility distribution of the SOA. The cloud condensation and ice nucleation activities of the SOAs undergoing multiphase reactions were measured by a Cloud Condensation Nucleus Counter and a Continuous Flow Diffusion Chamber in real-time to derive hygroscopicity parameter κ and ice freezing fraction, respectively.
Our result suggested that 20% of the inorganic sulfate was converted to organosulfates (OS) based on sulfate apportionment with AMS measurements, when reacting under the atmospherically relevant acidity. The sulfate equivalent mass fraction of OS was also higher with acidic seeds with the result from AMS being qualitatively consistent with the nano-DESI analysis. The κ of the bulk SOA was highly dependent on the volume fraction of organic aerosols. However, with the same organic fraction, the κ was lower under acid environment due to the higher concentration and lower κ of OS. The INP frozen fraction was higher for α-pinene-derived SOAs with acidic seeds due to the abundant OS formed and its higher viscosity, validated by the SEM images. Our study concludes that models should include the OS generation in SOA formation to constrain the uncertainties related to SOA-cloud interaction.