Detailed Comparison of Chamber Measurements and Mechanistic Predictions to Improve Understanding of SOA Formation Mechanisms
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 knowledge of these mechanisms derives from chamber experiments coupled with mass spectrometric measurements of the aerosol chemical composition which provide time-resolved measurements of individual species and measurements of ensemble properties such as elemental ratios and SOA yields. However, these measurements have inherent limitations, and there are major 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 core 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) to improve our understanding of the oxidation mechanisms of multiple VOCs. The chamber experiments were conducted with a suite of instruments measuring the majority of the secondary organic carbon in the gas and particle 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 suggest edits to the model (e.g., more accurate reaction rate predictions, branching ratios, etc.) while model results disambiguate chamber mass spectrometry data, provide information about functional groups, and help constrain physical processes such as partitioning among the gas, particles, and walls. Preliminary results show great promise for this model-measurement comparison strategy. 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.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.A44G..07M
- Keywords:
-
- 0305 Aerosols and particles;
- ATMOSPHERIC COMPOSITION AND STRUCTURE;
- 0317 Chemical kinetic and photochemical properties;
- ATMOSPHERIC COMPOSITION AND STRUCTURE;
- 0322 Constituent sources and sinks;
- ATMOSPHERIC COMPOSITION AND STRUCTURE;
- 0365 Troposphere: composition and chemistry;
- ATMOSPHERIC COMPOSITION AND STRUCTURE