Rationale
Policies for air quality, climate and ecosystem services are made with the aid of predictive numerical models. These models describe the main processes driving the evolution of the species for various space and time scales. The description of the chemical transformations occurring in the atmosphere is one common feature of these models. Models use the concept of chemical mechanisms to describe the chemical transformations occurring in the atmosphere. Distinct chemical mechanisms are nowadays available in the literature, with various degree of complexity matching particular focuses and computational constraints. My research activities fall within the general framework of modeling the chemistry of the troposphere and focus in particular to the development of such chemical mechanisms.
Modeling the tropospheric oxidation of organic matter
Understanding the atmospheric oxidation of organic species is a central issue to assess the impacts of the primary emissions by human and natural activities. For example, oxidation of organic matter leads to elevated ozone concentrations and secondary organic aerosols (SOA), ultimately leading to a degraded air quality in the vicinity of large emission sources (e.g. urban environment or megacity plumes). Similarly, chemistry of the troposphere controls ozone levels, methane lifetime and the formation of particulate matter which are all climate contributors. However, the description of the oxidation of organic compounds in the air quality and climate models is challenging, owing to the complexity of the processes involved. To date, the development of chemical mechanism has been carried mostly manually. This manual construction is extremely time-consuming and the revision of the mechanisms as a whole or their expansion has been proved to be impracticable when the organic skeleton of the species exceeds a few carbon atoms. Automated tools are nowadays needed to manage the development of tropospheric oxidation mechanisms for organic compounds.
Explicit
chemical mechanisms?
Explicit chemical mechanisms reflect the current fundamental understanding of the transformations occurring in the atmosphere and therefore occupy a particular position in the mechanism hierarchy. Indeed, these explicit mechanisms are either used (i) as a standard reference mechanism to assess the strengths and weaknesses of other simplified mechanisms or (ii) as a benchmark for the development of parameterizations for chemical transport model. Explicit mechanisms therefore provide a critical link between fundamental studies of the chemical processes and air quality or climate models ultimately used for the development of environmental policies.
The GECKO-A modeling tool
Automation is required for the development of explicit organic mechanisms based on a sound and sustainable
approach. My research is mainly devoted to the development and application of such a modeling tool: the
GECKO-A software (Generator for Explicit Chemistry and Kinetics of Organics in the Atmosphere).
GECKO-A is a unique tool for the automatic writing of chemical mechanism of organic species.
The tool generates chemical schemes according to a prescribed protocol assigning reaction pathways and
kinetic data on the basis of experimental data and structure-activity relationships. The generated chemical
mechanisms are not conceptually different than those written manually, with the advantage to be fast and easy
to maintain and update. Mechanisms of several million species have thus been generated and the resulting
set of differential equations has been successfully solved. These mechanisms have been extended to phase
equilibria and, for the first time, the formation of secondary organic aerosols using a fully explicit
model has been simulated. Click here
to learn more about the GECKO-A modeling tool.