Abstract View
Homogeneous Nucleation of Carbon Dioxide from 30-90 K: The Transition from Barrier-Controlled to Barrierless Nucleation
KAYANE DINGILIAN, Martina Lippe, Ruth Signorell, Barbara Wyslouzil, The Ohio State University
Abstract Number: 197
Working Group: Aerosol Physics
Abstract
Characterizing the nucleation of carbon dioxide (CO2) from the gas phase is crucial to understanding processes as diverse as carbon capture, refrigeration cycles, and cloud formation on Mars. Here, we explore the homogeneous phase transition of CO2 for temperatures ranging from ~30 to ~90 K and pressures spanning about four orders of magnitude. The broad range of conditions is achieved by combining results from experimental setups at OSU and ETH, where both experiments rely on a supersonic expansion to rapidly cool selected gas mixtures. In the OSU experiments, nucleation occurs within the diverging portion of the nozzle, and particle formation rates are based on the results of pressure trace measurements and small angle X-ray scattering experiments. In the ETH experiments, nucleation occurs in a uniform post nozzle flow and nucleation is characterized using single-photon ultraviolet ionization coupled with mass spectrometry. Despite the differences in experimental setups and gas compositions, there is excellent agreement between the onset data in the region of overlap. Experimental nucleation rates measured in the OSU setup are, however, two to three orders of magnitude higher than those determined in the ETH apparatus. This difference is consistent with the degree to which non-isothermal nucleation effects play a role. In particular, if the measured rates are scaled by non-isothermal correction factors to determine the intrinsic nucleation rates, remarkable consistency is achieved between the data sets. Furthermore, the combined data suggests that, in this measurement range, the nucleation process changes from one in which particle formation is controlled by a barrier to one in which the barrier vanishes and the kinetics of dimer formation controls the phase transition rate.