AAAR 35th Annual Conference October 17 - October 21, 2016 Oregon Convention Center Portland, Oregon, USA
Abstract View
Evaporation of Alpha-pinene SOA at Atmospherically Relevant Humidity Range
TAINA YLI-JUUTI, Aki Pajunoja, Angela Buchholz, Olli-Pekka Tikkanen, Celia Faiola, Olli Väisänen, Hao Liqing, Eetu Kari, Otso Peräkylä, Olga Garmash, Manabu Shiraiwa, Mikael Ehn, Kari Lehtinen, Annele Virtanen, University of Eastern Finland
Abstract Number: 269 Working Group: Aerosol Chemistry
Abstract Climate effects of secondary organic aerosols (SOA) are affected by the dynamic processes that SOA goes through in the atmosphere. Here, we investigate the factors that affect the evaporation of alpha-pinene SOA particles. SOA was generated by alpha-pinene ozonolysis in a flow tube. A size selected particle population was conditioned with a desired RH (dry, RH 40 % or RH 80 %) and sampled either through varying length of tubing or led to a 100 L stainless steel residence time chamber before the sampling. This allowed for monitoring the particles’ size evolution over a time line from few seconds to few hours. The evaporation rates were analyzed using a liquid-like particle evaporation model and a multi-layer particle evaporation model which includes particle phase diffusion. Both models presented the organic compounds with a volatility basis set (VBS). The evaporation was slower under dry conditions than under humid conditions, and in all cases slower than predicted based on a previously determined VBS without any particle phase diffusion limitations. We determined the initial particle volatility distribution by fitting the liquid-like particle model to the experimental data at RH 80 % using the genetic algorithm. A large mass fraction in the low-volatile VBS bins was needed to capture the evaporation. Using this initial volatility distribution we investigated the effect of particle phase diffusion limitations on the evaporation rate at RH 40 % and dry conditions. We found that particle viscosities consistent with previous studies could explain the slower evaporation at dry conditions compared to RH 80 %. However, a strong composition dependence in viscosity was required. The particle evaporation rates were similar at RH 40 % and RH 80 %. This suggests that the particle phase diffusion limitations had less effect at RH 40 % compared to the dry conditions.