Axis 2: Chemical processes

Work in this axis is oriented in particular to the study of the radical budget. Its knowledge is essential for assessing the chemical reactivity of the troposphere. Observations and simulations show in certain cases significant discrepancies and unexplained gaps.

In a polluted environment, two complementary approaches are considered :

- experiences of chemical closure enabling a direct comparison between concentrations of simulated and observed radicals, especially during field campaigns at sub -urban sites (Grignon and SIRTA/ Palaiseau).

- laboratory experiments exploring the today unknown potential, of some urban surfaces with photocatalytic proporties to produce reactive compounds (HONO and HCHO), which would make these surfaces additional sources of HOx radical formation in an urban atmosphere.

In a clean or moderately polluted environment, we assess the effect of the vertical redistribution of reactive species in convective systems on photochemical processes and specifically on the rate of ozone production, for example from airborne observations obtained during the AMMA campaign.

These activities combine in a systematic way observations and chemical 0D modeling. The very explicit simulation of atmospheric chemistry with the GECKO-A model is described in the theme "Becoming carbon ". Ina Lagrangian mode, GECKO-A will simulate different paths of secondary organic aerosol formation. Results will be compared to measurements carried out in the Paris pollution plume during the MEGAPOLI campaign. Moreover, simulations with this explicit model will provide a reference to develop reduced modules best suited for 3D modeling (axis 3).