Grantee Research Project Results

2022 Progress Report: 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 May 10, 2025
Project Period Covered by this Report: August 1, 2021 through July 31,2022
Project Amount: $799,667
RFA: Chemical Mechanisms to Address New Challenges in Air Quality Modeling (2019) RFA Text | Recipients Lists
Research Category: Watersheds , Endocrine Disruptors , Environmental Engineering , Air Quality and Air Toxics , Air

Objective:

The overarching goal of this work is the development of a systematic, general approach towards development of mechanisms (both 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. This will be done using a state- of-the-art chemical mechanism generator (GECKO-A), constrained by comprehensive laboratory measurements of the evolving product distributions from a range of organic oxidation systems. These laboratory oxidation data will be compared to predictions from the explicit chemical mechanism using key chemical properties of the organics (carbon oxidation state, OS_C, and carbon number, n_C), and the effects of changes to structure-activity relationships (SARs) on mechanism- measurement agreement will be explored. The mechanism will be reduced “on the fly” by binning by OS_C and n_C. Chemical transport modeling (GEOS-Chem) will then be used to investigate how inclusion of such mechanisms affects air quality predictions.

Progress Summary:

Y2 efforts centered on components of Tasks 1, 2, and 4 of the project, involving the comparison of laboratory data and GECKO predictions, the examination of how key parameters used in GECKO affect these comparisons, and the inclusion of mechanisms of various levels of complexity within a chemical transport model (GEOS-Chem). First, we continued mechanism- measurement comparisons for a number of systems previously studied in our environmental chamber (OH + n-butane, isoprene, toluene, trimethylbenzene, and a-pinene, all under conditions in which reactions with NO dominate RO₂ chemistry). We expanded our Y1 tests examining how changing model parameters can affect model-measurement agreement, by removing “manually- inputted” reactions, and modifying a wider range of chemical parameters than before (alkoxy chemistry, organic nitrate yields, rates of photolysis and ozonolysis reactions, etc.). These did not lead to substantial improvements in mechanism-measurement agreement across all reactions studied, suggesting the need to take a broader, more systematic approach towards SAR adjustments. Finally, organic nitrate formation was predicted by mechanisms of various levels of complexity and compared against results from a series of field campaigns in the United States.

Future Activities:

A new researcher will be hired to lead the model-development component of this work. Model parameters (e.g., structure-activity relationships and their associated parameters) will be changed using a “Monte-Carlo” approach (a less directed, more random approach than was taken in Y1-2); this will ideally enable the identification of possible scenarios that lead to improved agreement between GECKO predictions and laboratory measurements. In addition, development of the “on- the-fly” approaches to mechanism reduction (binning by OS_C and n_C) will begin, requiring modifications to the overall structure of the GECKO software.

Journal Articles:

No journal articles submitted with this report: View all 8 publications for this project

Supplemental Keywords:

Structure-activity relationships, secondary organic aerosol, air quality models

Progress and Final Reports:

Original Abstract

The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.