BIO-MAIDO

The BIO-MAIDO project aims at better understanding the chemical and biological multiphasic mechanisms that control the Secondary Organic Aerosol (SOA) formation. The tropical environment of the Reunion Island represents an ideal area to study SOA formation by the multiphasic atmosphere since: (1) numerous biogenic volatile organic compounds, precursors of SOA are emitted in huge amount and the high solar intensity flux and the temperature favours their chemical transformations; (2) the high occurrence of fogs and clouds over the area can lead to the formation of SOA by aqueous phase processes (chemistry and biology). The strategy adopted here is based on an intensive field campaign with the objective to characterize primary sources of gases and aerosols and to evaluate multiphasic pathways controlling the formation and oxidation of SOA. This work is done in synergy with modelling investigations using a 0D process cloud model (CLEPS) together with a 3D chemistry/transport model (Meso-NH). The field campaign will be deployed on two sites: one in source area with biogenic emissions and submitted to fog (mid-slope site in forest); one in receiver zone with transformed and oxidized air masses (Maïdo observatory). Previous results from numerical simulations and observations show the presence at the Maïdo observatory of air masses coming along the slope and mixing anthropogenic, marine and biogenic influences. Simulations of trajectory origins along the slope of the Maïdo will be performed during the campaign to help the interpretation of in-situ observations. Marine and anthropogenic sources will be assessed thanks to results from the OCTAVE project (Oxygenated Compounds in the Tropical Atmosphere: Variability and Exchange), chemical markers identification and back-trajectories. A particular attention will be paid of to the boundary layer features thanks to the MARLEY lidar deployed on a mobile pick-up truck. State-of-art instrumentations will be deployed for the characterization of SOA precursors gases including primary compounds, the physico-chemical properties of aerosol particles and the bio-physico-chemical properties of clouds forming along the slope of the Maïdo. The campaign will be synchronize with the ANR NEPHELAE campaign, which will document the 4D structure of clouds thanks to a fleet of autonomous aerial vehicles that coordinate themselves in real-time as an intelligent network. These sets of observation will help understand the formation of SOA in a humid tropical atmosphere by improvement of the CLEPS and Meso-NH models. The French INSU labelled 3D Meso-NH model will benefit from the observations and the simulations performed with the 0D CLEPS model to improve its parameterizations of SOA formation from gas phase and cloud droplets processes including bacterial activities. This last point is very innovative as never studied until now.