Grantee Research Project Results
2024 Progress Report: Leveraging comprehensive organic oxidation experiments for the development of improved atmospheric chemical mechanisms
EPA Grant Number: R840005Title: 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, 2023 through July 31,2024
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/improvement 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, 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 reduced chemical mechanisms using key species, species classes, and/or chemical properties of the organics. From these results, the effects of changes to the mechanism and/or structure-activity relationships (SARs) on mechanism-measurement agreement will be explored. Finally, chemical transport modeling will then be used to investigate how inclusion of such mechanisms affects air quality predictions.
Progress Summary:
The main research efforts in Y4 centered on comparisons between detailed chamber measurements and model predictions. The specific focus was the ability of EPA’s new Community Regional Atmospheric Chemistry Multiphase Mechanism (CRACCM2) to describe the observed chemistry of α-pinene + OH, across a range of RO2 chemistries. Such comparisons required development of a novel workflow that connects explicit and reduced models. First, chamber chemistry was simulated and key chamber conditions parameterized using CRACMM2; then species measured in the lab were mapped to lumped species in the mechanism, using an explicit mechanism generator updated with new kinetic measurements; and finally, the detailed model predictions were compared to measured oxidation products, as a function of reaction time and RO2 chemistry. Overall the agreement for the various organic species was found to be reasonably good, across a range of RO2 reactivities, though some disagreements were seen for specific species (e.g., acetone) and species classes (peroxides, nitrates), highlighting potential future improvements to both measurements and mechanisms. In addition, we carried out a modeling study examining the definitions of chemical regimes that control tropospheric ozone formation.
Future Activities:
In Y5 we will continue to focus on chamber-mechanism comparisons, first by continuing work on the α-pinene + OH system. Key efforts will include improvements to the mapping protocol; the detailed examination of the role of RO2 branching; and the comparison of not just gas-phase species but particle-phase species as well. From there we will expand our work to cover a wider range of chemical systems, such as isoprene oxidation by OH, aromatic oxidation by OH, and terpene oxidation by O3. From these measurement-model comparisons, we will systematically examine changes to CRACCM2 chemistry and parameters (rates, products) that can lead to improved agreement, ideally across all hydrocarbons and RO2 fates studied.
Journal Articles:
No journal articles submitted with this report: View all 8 publications for this projectSupplemental Keywords:
Structure-activity relationships, secondary organic aerosol, air quality modelsProgress and Final Reports:
Original AbstractThe 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.