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VOC measurements in the marine tropical atmosphere

Research Topic Chapter
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Although volatile organic compounds (VOCs) have a large impact on the oxidative capacity of the atmosphere and on climate, their sources and sinks are not well constrained, especially over tropical marine regions. In the context of the BRAIN project OCTAVE, BIRA-IASB started long-term VOC measurements at the high-altitude Maïdo station on Réunion Island in the Indian Ocean. These measurements are needed to identify and quantify VOC sources and sinks on the island, as well as their seasonal evolution, by means of statistical analysis, back trajectory calculations, and 3-dimensional modelling.
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The Brain-be OCTAVE project, which is a collaboration between BIRA-IASB (coordinator), ULB and CNRS, was started in 2017 and aims at reducing those uncertainties by using an integrated approach combining in situ measurements, satellite retrievals and modelling.

In the framework of this project, BIRA-IASB started collecting a two-year continuous dataset of (O)VOC concentrations at the Maido observatory (Fig. 1), a high-altitude (2200 m) atmospheric observatory at Réunion Island (21.06° S, 55.39° E) which is located in the Indian Ocean. These data are complementary to the FTIR column concentrations of IR active trace compounds that are being collected by BIRA-IASB at this location since 2013.

(O)VOC measurements are performed on-line with a fast and sensitive proton transfer reaction mass spectrometry (PTR-MS) instrument (Fig. 2 and 3), which is fully operated by remote control. Typical molecules which are characteristic for the major (O)VOC sources at Réunion Island (ocean, vegetation, anthropogenic activities, biomass burning) are continuously measured at high-time resolution.

The long-term dataset, which is quite unique in this part of the world, will then be used to determine the contribution of the different sources to the air composition at Maido and their seasonal variability.

Exploitation of the data set will require the use of advanced statistical techniques, back trajectory calculations and 3D modelling.

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Figure 2: Experimental set-up for measuring the VOC concentrations.
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Figure 3: Ambient air sampling from the roof of the Maido Observatory at Réunion Island.