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Humidity Dependence of the Condensational Growth Rate of Secondary Organic Aerosol Particles
YIMING QIN, Jinghao Zhai, Paul Ohno, Jianhuai Ye, Yuemei Han, Pengfei Liu, Rahul Zaveri, Scot T. Martin, Harvard University
Abstract Number: 183
Working Group: Aerosol Chemistry
Abstract
The condensational growth rate of the secondary organic aerosol (SOA) particles has a profound impact on the health and climate perturbation of atmospheric particles. This growth rate is typically represented in atmospheric models with a fixed value, regardless of the relative humidity (RH), even though the actual RH in the atmosphere varies widely with the location, season, and time. Whether and how RH affects the growth rate of atmospheric particles remains unclear. The study herein investigates the humidity dependence from 0% to 75% RH of the condensational growth of SOA particles derived from α-pinene ozonolysis in a continuously mixed flow reactor. A repeating pattern of the rapid growth of nanoparticles to larger particles of several hundred nm was observed even the total particle number concentration. A notable and monotonous increase of the particle area growth rate, from 1.1 ± 0.6 to 4.6 ± 0.4 nm2 s-1, were observed for a shift in RH from 0% to 75%. Aerosol mass spectrometer analysis shows that changes in chemical composition do not appear to explain the changes in the growth rate. However, mass transfer kinetic model (Model for Simulating Aerosol Interactions and Chemistry, MOSAIC) simulation shows that changes in the diffusivity inside the particle and the surface mass accommodation coefficients can reproduce the RH-dependent growth phenomena. The findings presented herein highlight the need to incorporate physical properties of atmospheric particles in probing and modeling the continuous size evolution of the particles at varying environmental conditions, which is expected to significantly influence the lifetime and potential health and climate impacts of atmospheric particles.