Grantee Research Project Results
2023 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, 2022 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
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, OSC, and carbon number, nC), 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 OSC and nC. Chemical transport modeling (GEOS-Chem) will then be used to investigate how inclusion of such mechanisms affects air quality predictions.
Progress Summary:
The main research efforts in year 3 centered on Task 1 of the project, the comparison of laboratory data and GECKO predictions, as part of a new collaboration with researchers at NCAR. We find decent agreement between the two in terms of overall carbon partitioning (organic gases, inorganic gases, particulate organic carbon, and wall-deposited species); however the predicted and measured composition of the gas-phase species differed considerably. Recently we identified the primary source of discrepancy between chamber measurements and mechanistic predictions, related to peroxyacyl nitrates (PANs, of formula RC(O)OONO2). GECKO predicts high levels of these species, but measurements indicate very low high concentrations (<10 parts-per-billion carbon) of species with formulas corresponding to PANs. It is currently unclear whether this difference is because GECKO overpredicts such species (with formation that is too fast or loss that is too slow), or because our mass spectrometric instruments do not measure them efficiently, or some combination of the two.
Future Activities:
In early 2024, a new postdoctoral associate (and possibly a graduate student as well) will begin working on this project full time. After an initial period for training on GECKO and familiarization with chamber data, efforts will focus on: (1) examination of the model-measurement discrepancy for PAN compounds, with the goal of reconciling predictions and chamber measurements; (2) automated exploration of changes to GECKO model parameters to improve model-mechanism agreement; (3) development of “on-the-fly” approaches to mechanism reduction; and (4) the comparison of predicted vs. measured dependences of product distributions on RO2 chemistry.
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.