10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
Abstract View
Characteristics and Relative Humidity Dependence of the Condensational Growth of Secondary Organic Aerosol Particles in a Continuously Mixed Flow Reactor
YUEMEI HAN, Jinghao Zhai, Chlóe Vercruysse, Yiming Qin, Jianhuai Ye, Scot T. Martin, Harvard University
Abstract Number: 959 Working Group: Aerosol Physics
Abstract Condensation of low volatility and semivolatile organic gas-phase species is an important atmospheric process for nucleated particles growing up to large sizes that might act as cloud condensation nuclei to impact the climate. The formation and subsequent growth of atmospherically relevant aerosol particles have been investigated extensively using laboratory environmental chambers. However, most of the previous studies are performed under limited relative humidity (RH) or even dry conditions, differing from those in the ambient atmosphere over a range of RH values. The influence of RH on the condensational growth and evolution of secondary organic material (SOM) remains poorly understood. In the current study, SOM was generated from the dark ozonolysis of alpha-pinene in a continuously mixed flow reactor, the Harvard Environmental Chamber, from dry to high RH conditions. The condensational growth of particle population was characterized from their number-size distributions measured in real-time using a scanning mobility particle sizer. The chemical composition of SOM particle was measured continuously with aerosol mass spectrometry. A strong nucleation of SOM particles occurred immediately after turning on the ozone lamp, followed by a series of particle growth events throughout the entire experiments. The chemical composition and oxidation state of SOM particles changed slightly with variable RH, which is possibly due to the influence of RH on the gas-particle partitioning of condensable organic compounds. The condensational growth rate and the time scale of growth will be derived from the evolution of particle number-size distributions for the individual RH values. The potential dependence on RH will be parameterized and incorporated into an analytical equation to optimize the characterization of condensational growth of SOM particle. Results from this study would be helpful to understand the gaps in the condensational growth of aerosol particles in laboratory studies compared to those in the real atmosphere.