Grantee Research Project Results
2021 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 July 31, 2023 (Extended to July 31, 2025)
Project Period Covered by this Report: August 1, 2020 through July 31,2021
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
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 stateof-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, OSC, and carbon number, nC), and the effects of changes to structure-activity relationships (SARs) to mechanismmeasurement agreement will be explored. The mechanism will be reduced “on the fly” by binning by OSC and nC; and finally chemical transport modeling (GEOS-Chem) will be used to investigate how inclusion of such mechanisms affects air quality predictions.
Progress Summary:
In Y1 of this project we made mechanism-measurement comparisons for a number of chemical systems (OH+trimethylbenzene, isoprene, n-butane, toluene, and α-pinene, all under high-NO conditions). A number of comparison approaches were attempted, including an isomer-by-isomer comparison, in which species of the same formula were compared; a modified isomer-by-isomer approach which takes into account decomposition processes within the mass spectrometers; and a binned approach that instead compares carbon oxidation state (OSC) and carbon number (nC). This last approach was found to provide the clearest comparison, and is least susceptible to decomposition processes or calibration errors. Based on this comparison a “similarity metric” was developed, providing a quantitative standard by which changes to the GECKO mechanism (namely the underlying SARs) can be assessed, as function of reaction time (atmospheric aging). We then carried out preliminary tests of how changing SARs describing key branch points (related to alkoxy and peroxy radical fate) affected this agreement. However, using this focused approach we were unable to find any changes that uniformly and clearly improved mechanism-measurement agreement, pointing to directions for future work.
Future Activities:
With our campus largely re-opened and travel becoming more straightforward, we plan to hire two postdoctoral associates to carry out the major tasks of this project. A key goal of their research will be to continue the comparisons between laboratory data and GECKO simulation results, and to adjust the SARs within GECKO to try to improve agreement (Tasks 1 and 2 of the project), as well as to begin the development of the “on-the-fly” approaches to mechanism reduction (Task 3). In Y2 postdocs will travel to LISA for a three-week training with the developers of GECKO, in order to become more familiar with the mechanism generator and its structure.
Journal Articles:
No journal articles submitted with this report: View all 5 publications for this projectSupplemental Keywords:
Structure-activity relationships, secondary organic aerosol, air quality models
Progress 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.