10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
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Formation and Evaporation Kinetics of Organic Aerosol from Oxidation of Precursor Mixtures by the Nitrate Radical
THOMAS BERKEMEIER, Masayuki Takeuchi, Gamze Eris, Michael Walker, Brent Williams, Nga Lee Ng, Georgia Institute of Technology
Abstract Number: 1515 Working Group: Aerosol Physics
Abstract Formation of Secondary Organic Aerosol (SOA) was investigated at the Georgia Tech Environmental Chamber (GTEC) facility from separate, simultaneous and sequential oxidations of the precursors α-pinene and limonene with the nitrate radical (NO3).
For the detailed characterization of nitrated and non-nitrated reaction products in the gas and particle phases, GTEC was equipped with a High-Resolution Time-of-Flight Chemical Ionization Mass Spectrometer (HR-ToF-CIMS) coupled with a Filter Inlet for Gases and AEROsols (FIGAERO) as well as a HR-ToF-MS with the Volatility and Polarity Separator (VAPS)1. Aerosol formation was initiated at low temperatures of 5 °C and evaporation of product species monitored during step-wise heating to 42 °C. α-pinene and limonene SOA showed distinct evaporation patterns upon increase in chamber temperature.
The measurement data is analyzed using a novel kinetic modelling approach that utilizes a kinetic multi-layer model to describe the coupling of mass transport and chemical reactions in complex multiphase reaction systems. Special attention was given to gas-phase chemistry, vapor wall loss, diffusion in the particle bulk and temperature-dependent gas-particle partitioning of reaction products. The model simulations, along with FIGAERO-CIMS and VAPS-MS data, allow for distinction of the volatility distributions of nitrated and non-nitrated reaction products. We present evidence for kinetic limitations in the evaporation of organic material and a phase transition during the heating process. A semi-explicit chemical mechanism is presented that represents the experimental data and simplifies the Master Chemical Mechanism (MCM)2 for the use in complex modelling applications. The chemical mechanism was generated using the Monte-Carlo Genetic Algorithm (MCGA)3 as global optimization tool.
References [1] Martinez, R.E., et al.: Development of a Volatility and Polarity Separator (VAPS) for Volatility- and Polarity-Resolved Organic Aerosol Measurement, Aerosol Sci. Tech.50(3), 255-271, 2016. [2] Saunders, S. M., Jenkin, M. E., Derwent, R. G. & Pilling, M. J.: Protocol for the development of the Master Chemical Mechanism, MCM v3 (Part A): tropospheric degradation of non-aromatic volatile organic compounds. Atmos. Chem. Phys.3, 161–180, 2003. [3] Berkemeier, T. et al.: Technical note: Monte Carlo genetic algorithm (MCGA) for model analysis of multiphase chemical kinetics to determine transport and reaction rate coefficients using multiple experimental data sets. Atmos. Chem. Phys.17, 8021–8029, 2017.