Preliminary Results From The Farce 2015 Campaign: Multidisciplinary Study Of The Forest-Gas-Aerosol-Cloud System On The Tropical Island Of La Reunion

The Forests gAses aeRosols Clouds Exploratory (FARCE) campaign was conducted in March-April 2015 on the tropical island of La Reunion. For the first time, several scientific teams from different disciplines collaborated to provide reference measurements and characterization of La Reunion vegetation, volatile organic compounds (VOCs), biogenic VOCs (BVOCs), (bio) aerosols and composition of clouds, with a strong focus on the Maido mountain slope area. The main observations obtained during this 2-month intensive field campaign are summarized. They include characterizations of forest structure, concentrations of VOCs and precursors emitted by forests, aerosol loading and optical properties in the planetary boundary layer (PBL), formation of new particles by nucleation of gas-phase precursors, icenucleating particles concentrations, and biological loading in both cloud-free and cloudy conditions. Simulations and measurements confirm that the Maido Observatory lies within the PBL from late morning to late evening and that, when in the PBL, the main primary sources impacting the Maido Observatory are of marine origin via the Indian Ocean and of biogenic origin through the dense forest cover. They also show that (i) the marine source prevails less and less while reaching the observatory; (ii) when in the PBL, depending on the localization of a horizontal wind shear, the Maido Observatory can be affected by air masses coming directly from the ocean and passing over the Maido mountain slope, or coming from inland; (iii) bio-aerosols can be observed in both cloud-free and cloudy conditions at the Maido Observatory; (iv) BVOC emissions by the forest covering the Maido mountain slope can be transported upslope within clouds and are a potential cause of secondary organic aerosol formation in the aqueous phase at the Maido Observatory; and (v) the simulation of dynamics parameters, emitted BVOCs and cloud life cycle in the Meso-NH model are realistic, and more advanced Meso-NH simulations should use an increased horizontal resolution (100 m) to better take into account the orography and improve the simulation of the wind shear front zone within which lies the Maido Observatory. Using various observations and simulations, this work draws up an inventory of the in situ studies that could be performed in La Reunion and at the Maido Observatory. It also aims to develop scientific collaborations and to support future scientific projects in order to better understand the forest-gas-aerosol-cloud system in an insular tropical environment.