AAAR 35th Annual Conference October 17 - October 21, 2016 Oregon Convention Center Portland, Oregon, USA
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Chemistry, Morphology, and Cloud Activation: Chemical Composition Measurements of α-pinene SOA at Low Temperature with a FIGAERO-CIMS
CLAUDIA MOHR, Harald Saathoff, Aki Pajunoja, Annele Virtanen, Wei Huang, Xiaoli Shen, Robert Wagner, Yvette Gramlich, Karlsruhe Institute of Technology
Abstract Number: 264 Working Group: Aerosols, Clouds, and Climate
Abstract During transport of newly formed secondary organic aerosol (SOA) from the lower troposphere to the upper troposphere where cloud formation becomes important, temperature and relative humidity (RH) conditions vary significantly. To simulate SOA uplifting and investigate the influence of atmospherically relevant temperature and RH conditions on phase state, morphology, chemical composition, and (ice) cloud activation in the atmosphere, we used 2 chambers at the Karlsruhe Institute of Technology (KIT). α-pinene SOA was generated in a smaller stainless steel chamber at room temperature and then transported into the much larger AIDA chamber (84 m3, aluminum) kept at temperatures between 298 and 208 K. RH in the AIDA was then gradually increased from ~ 30% to ~95% to enable droplet or ice activation during an adiabatic expansion. The composition of the organic aerosol and its surrounding gas phase was measured with a Chemical Ionization Mass Spectrometer with a Filter Inlet for Gases and Aerosols (FIGAERO-CIMS) using I- as reagent ion. Viscosity of particles as a function of water uptake was investigated by the Aerosol Bounce Instrument.
We observed differences in chemical composition as well as water uptake behavior for organic particles under different temperature and humidity conditions. For semi-volatile compounds, thermograms from the FIGAERO show a shift towards larger maximum desorption temperatures with increasing AIDA RH at warm temperature, indicative of matrix effects or accretion reactions. Bounce measurements in the ABI indicate irreversible changes in the particles’ physicochemical properties with increased exposure to humid conditions. Such effects were not observed at cold temperatures.
The results show the importance of meteorological conditions during SOA formation and processing in the atmosphere (and the laboratory) on their physicochemical properties and consequently their climate effects via cloud formation.