Development, validation and integration of a new model-ready parameterization of N2O5 heterogeneous chemistry.EPA Grant Number: R840006
Title: Development, validation and integration of a new model-ready parameterization of N2O5 heterogeneous chemistry.
Investigators: Bertram, Timothy , Holloway, Tracey
Institution: University of Wisconsin - Madison
EPA Project Officer: Chung, Serena
Project Period: August 1, 2020 through July 31, 2023
Project Amount: $798,234
RFA: Chemical Mechanisms to Address New Challenges in Air Quality Modeling (2019) RFA Text | Recipients Lists
Research Category: Air , Air Quality and Air Toxics
Nitrogen oxides (NOx ≡ NO + NO2) play a central role in the production of tropospheric ozone and particulate nitrate aerosol. Accurate treatment of the chemical lifetime of NOx in chemical transport models is essential to robust prediction of air quality. Despite the central role of nocturnal nitrogen oxide chemistry, existing model parametrizations of key heterogeneous mechanisms, such as that of N2O5, are outdated in most chemical transport models.
The primary objective of this proposal is development and validation of a new chemically based parameterization for ϒ(N2O5) and Φ(ClNO2) that accounts for recent insights from laboratory and field measurements of N2O5 and ClNO2 heterogeneous chemistry, with a specific focus on the role of phase separation and aerosol water in regulating reactive uptake of N2O5. The chemically based parameterization will be constructed such that they can be readily integrated into CMAQv5.3 leveraging new advances in organic aerosol treatment in the model. We will then assess the impact of nocturnal nitrogen oxide chemistry on tropospheric O3 and particulate nitrate in two select urban regions (St. Louis, MO and Phoenix, AZ) during winter and summer. We hypothesize that the NOx lifetime (with respect to N2O5 heterogeneous chemistry) is a far too short in current models and that the product branching to ClNO2 is far too large.
We will construct a new version of the existing Bertram and Thornton  parameterization of ϒ(N2O5) that permits the organic fraction of aerosol to 1) phase separate, generating core-shell morphologies and 2) control aerosol liquid water content. Using the vast collection of existing laboratory and field measurements of ϒ(N2O5) we will determine the dependence of N2O5 diffusion, solubility and reaction kinetics on organic aerosol composition. The refined parameterization will then be included in CMAQ and validated against existing field determinations of ϒ(N2O5) and Φ(ClNO2). We will then assess the sensitivity of CMAQ derived morning NO2 vertical columns in two test regions (St. Louis, MO and Phoenix, AZ) to the model treatment of N2O5 chemistry and compare the model results with remote sensing measurements on NO2 vertical columns.
The primary outcome of the project is the development and integration of a new chemically based parameterization for ϒ(N2O5) and Φ(ClNO2) within CMAQ. This address research needs identified in the solicitation, including advancing the treatment of heterogeneous chemistry of important processes relevant to O3 and PM using explicit and condensed chemical mechanisms and what are the implications for air quality.
Heterogeneous and multiphase chemistry, satellite, NO2 vertical column, organic aerosol.