AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
Abstract View
Detailed Comparison of Chamber Measurements and Mechanistic Predictions to Improve Understanding of SOA Formation Mechanisms
JOSHUA MOSS, Abigail Koss, Kevin Nihill, Martin Breitenlechner, Alexander Zaytsev, Richard Valorso, Marie Camredon, Bernard Aumont, Frank Keutsch, Jesse Kroll, MIT
Abstract Number: 516 Working Group: Aerosol Chemistry
Abstract Elucidating the underlying chemical mechanisms pertaining to Secondary Organic Aerosol (SOA) formation and evolution via the oxidation of Volatile Organic Compounds (VOCs) is critical to improving our understanding of organic matter in the atmosphere. Much of our understanding of such mechanisms derives from experimental studies such as chamber experiments coupled with mass spectrometric measurements of the chemical composition of the gas and particle phases. These provide time-resolved measurements of individual species as well as measurements of ensemble properties such as elemental ratios and SOA yields. However, such measurements have inherent limitations such as those arising from the influence of walls and surfaces, and there are significant challenges associated with the interpretation of mass spectra in terms of detailed molecular composition. On the other hand, detailed chemical mechanisms enable the prediction of concentration profiles for a wide range of chemical species, but they are limited by a priori knowledge of the underlying chemistry and have not always been validated against experimental data. In this study, we carry out a detailed comparison of measured oxidation products (from a series of chamber studies) and results from a self-generating chemical mechanism (GECKO-A) in order to improve our understanding of the oxidation mechanisms of multiple VOCs. The chamber experiments were conducted with a suite of instruments that measured the majority of the product organic carbon in both the particle and gas phases. This enables the direct comparison with GECKO-A predictions, across various levels of detail, ranging from ensemble properties such as oxidation state and SOA yields to more granular data such as time series of individual molecular species. This comparison helps inform both the measurements and the model: differences between the predicted and measured results can suggest edits to the model (e.g., improved branching ratios) while model results can help clarify and disambiguate chamber mass spectrometry data and help constrain physical processes such as partitioning among the gas, particles, and walls. The ultimate objectives of this work are to yield novel insights into SOA oxidation mechanisms while also providing a template for future model-measurement comparisons.