Leveraging comprehensive organic oxidation experiments for the development of improved atmospheric chemical mechanisms

EPA Grant Number: R840005
Title: Leveraging comprehensive organic oxidation experiments for the development of improved atmospheric chemical mechanisms
Investigators: Kroll, Jesse H. , Heald, Colette L.
Institution: Massachusetts Institute of Technology
EPA Project Officer: Chung, Serena
Project Period: August 1, 2020 through July 31, 2023
Project Amount: $799,667
RFA: Chemical Mechanisms to Address New Challenges in Air Quality Modeling (2019) RFA Text |  Recipients Lists
Research Category: Air , Air Quality and Air Toxics

Description:

The atmospheric oxidation of organic compounds plays a central role in air quality, as it controls the formation of secondary species such as ozone and secondary organic aerosol. An understanding of air quality both in the present day and under various future scenarios therefore relies critically on accurate mechanisms that accurately describe this oxidation chemistry. Recent laboratory studies using novel analytical techniques that can measure multifunctional organic compounds offer exciting opportunities for the development and refinement of such chemical mechanisms. However there currently exist no systematic approaches for translating results from such lab studies into improved mechanisms, given the immense chemical complexity associated with atmospheric oxidation processes.

Objective:

The goal of this work is the development of a systematic, general approach towards development of mechanisms (explicit and reduced) for complex organic compounds, based on new laboratory datasets describing their oxidation chemistry, and in a way that conserves carbon and retains the organic species’ key chemical properties.

Approach:

The steps of the proposed mechanism-development approach are as follows: the comparison of laboratory oxidation data with results from an explicit chemical mechanism using key chemical properties of the organics (carbon oxidation state, OSC, and carbon number, nC); the systematic investigation of how changes to structure-activity relationships can improve mechanism-measurement agreement; the reduction of the mechanism via binning by OSC and nC; and the use of chemical transport modeling to investigate how inclusion of such mechanisms affects air quality predictions. These activities bring together four state-of-the-art tools/approaches: comprehensive laboratory measurements of the evolving product distributions from a range of organic oxidation systems, a chemical mechanism generator (GECKO-A) for the automated construction of explicit oxidation mechanisms, the OSC-nC framework for describing organic compounds, and a global chemical transport model (GEOS-Chem) to assess the implications of new mechanisms.

Expected Results:

This primary outcome of this project will be the development of a general, scalable approach towards the construction of chemical mechanisms that reproduce the key properties and reactivities of organic compounds. The specific focus of this work will be a few classes of organic species (alkanes, monoterpenes, and aromatics), and the study of those systems (e.g., model-measurement comparisons, the development of reduced mechanisms) is expected to lead to a greatly improved understanding of their chemistry. Moreover, the approaches explored here for these important classes of compounds can be applied to a wider range of chemical systems, as mechanisms are improved and new laboratory measurements become available

Supplemental Keywords:

structure activity relationships (SARs), secondary organic aerosol (SOA), air quality models