Explicit Modelling of the Multiphase Oxidation of Organic Compounds

Speaker: Bernard Aumont, Laboratoire Interuniversitaire des Systémes Atmosphériques (LISA), Universités Paris Est Creteil et Paris Diderot, France

When: Wednesday, August 13, 2014, 3:30 p.m. Mountain Time
Location: Room 2A305, DSRC (NOAA Building), 325 Broadway, Boulder
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Atmospheric oxidation of organic matter is a gradual process involving a myriad of gaseous intermediates usually denoted as secondary organic compounds (SOC). These intermediates are typically species bearing one or more functional groups, such as ketone, aldehyde, alcohol, nitrate or hydroperoxide moieties. Secondary organic compounds play a central role in the chemistry of the atmosphere, being directly involved in the HOx/NOx/Ox tropospheric budget, in the production of particulate matter via the formation low volatility organic compound and in cloud chemistry via the formation of water soluble organic compounds.

Explicit chemical mechanisms aim to embody the current knowledge of the transformations occurring in the atmosphere during the oxidation of organic matter. These explicit mechanisms are therefore useful tools to explore the fate of organic matter during its tropospheric oxidation and examine how these organic chemical processes shape the composition and properties of the gaseous and the condensed phases. Nevertheless, the explicit mechanism describing the oxidation of hydrocarbons with backbones larger than few carbon atoms involves millions of SOC, far exceeding the size of chemical mechanisms that can be written manually. Data processing tools can however be designed to overcome these difficulties and automatically generate consistent and comprehensive chemical mechanisms on a systematic basis.

The Generator for Explicit Chemistry and Kinetics of Organics in the Atmosphere (GECKO-A) has been developed for the automatic writing of explicit chemical schemes of organic species and their partitioning between the gas and condensed phases. GECKO-A can be viewed as an expert system that mimics the steps by which chemists might develop chemical schemes. GECKO-A generates chemical schemes according to a prescribed protocol assigning reaction pathways and kinetics data on the basis of experimental data and structure-activity relationships. In its current version, GECKO-A can generate the full atmospheric oxidation scheme for most linear, branched and cyclic precursors, including alkanes and alkenes up to C25.

Recent assessments and applications of the GECKO-A modeling tool will be presented, with a focus given to studies devoted to examine SOA formation and ageing, SOC phase partitioning and multiphase oxidation processes.