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Volatile organic compounds are essentials drivers of atmospheric chemistry and precursors of pollutants that constitute a threat for human health and the environment: ozone (O₃) and secondary organic aerosols (SOA) (Chameides & Davis, 1980; Andreae & Crutzen, 1997). Most VOC are biogenic (BVOC), and are not exhaustively quantified. In particular, managed ecosystems which represent up to 50% of land use in Europe, represent the largest potential emitter of BVOC. It is estimated that 55% of the emissions come from forest, 27% from agriculture and 18% from other land use (grasslands and wetlands) (Karl et al., 2009). Current estimates however do not account satisfactorily for emissions linked with agricultural practices due to a lack of data: slurry management, emissions from litter, pesticides.

In this project we will set up a new direct method able to measure the fluxes of the vast majority of BVOC from a panel of managed ecosystem in France: crops and managed forests. We will also measure emission from agricultural practices identified as major BVOC and SVOC (semi volatile) emitters and in particular field slurry application and litter decomposition. Additional measurements will be performed to establish the links between BVOC fluxes and ecosystem functioning. This will allow extrapolating our results and evaluate emission potential of BVOC by these ecosystems.

To reach our objectives we will set up an eddy covariance (EC) method for measuring BVOC fluxes, using a state of the art PTR-TOF-MS (Time of flight Proton Transfer Mass Spectrometer) instrument. The sensitivity and acquisition frequency of this instrument indeed allow EC flux measurement for a large spectrum of BVOC. This instrument and complementary GC-MS (gas chormatography) measurements will also be used to measure BVOC fluxes in each compartment of the ecosystem and from slurry and litter in the laboratory.

Although the PTR-TOF-MS measures a large number of compounds, it is not an exhaustive measurement.  Hence, we will set up an indirect validation method by measuring the OH reactivity of the atmosphere which by comparison with the measured BVOC determines whether there are missing compounds in the balance.