Axis 3: The evolution of organic carbon and its role in the transport of nitrogen oxides
Tropospheric organic matter sees its functionalization grow over its oxidation in the atmosphere. Among the chemical functions incorporated into the carbon skeleton, some are likely to be returned in subsequent transformations of molecules that support them. Secondary organic compounds can then become essential reservoirs to long distance transport of photochemical active species. This is particularly the case of organic nitrates (RONO2) produced in the atmosphere by the oxidation of VOCs in rich nitrogen oxides environments and which have lifetimes long enough to be transported over long distances and thus play the role of species reservoirs of NOx (Figure 1).
Figure 1: Role of organic nitrates in the long distance transport of reactive nitrogen
Among formed nitrates, we find alkyl nitrates, but also polyfunctional organic nitrates such as hydroxyalkyl nitrate from the oxidation of alkenes by OH radical, the dinitrates derived from the oxidation of unsaturated VOC by the nitrate radical or from oxygenated nitrates from the oxidation of NO3 of unsaturated oxygenated compounds. During field campaigns, it has thus been shown that polyfunctional organic nitrates represent a significant share of total organic nitrates.
The knowledge of the chemistry of these polyfunctional organic nitrates remains today very flawed. Therefore, LISA is involved in a study to improve the knowledge of these processes by combination of laboratory and modeling experiments. More specifically, it is :
- Enhanced the knowledge of the kinetics and mechanisms of formation of polyfunctional organic nitrates out of unsaturated VOCs oxidation by the NO3 radical by experiments in simulation chambers at LISA,
- Study the kinetics and mechanisms of degradation of polyfunctional organic nitrates by experiments in simulation chambers in order to improve the knowledge of their life spans, on the other hand to measure the amounts of NOx emitted by these processes. This study involves synthesizing prior polyfunctional organic nitrates which are not commercially available (Figure 2).
Figure 2: Device for the synthesis of organic nitrates
- Characterize the evolution of reactive nitrogen in urban and continental plumes using 0D simulations carried out with the automatic generator of chemical schemas GECKO-A updated with all of these experimental data
- Evaluate the impact of the geographical redistribution of NOx induced by organic nitrates on the assessments of oxidants to a continental-scale using the 3D CHIMERE model.