Comprehensive Observations of the Biosphere-Atmosphere Exchange of Reactive Carbon during the Flux Closure Study (FluCS)

The bidirectional exchange of reactive biogenic volatile organic compounds (BVOC) between the atmosphere and terrestrial biosphere is an important process that can regulate the abundance of key oxidants such as the hydroxyl radical (OH) and ozone (O3) as well as control aerosol budgets. However, limited understanding of these fluxes prevents an accurate representation of their effects in current models. Key knowledge gaps include: 1.) an underrepresentation of reactive BVOC in chemical mechanisms, 2.) lack of knowledge on the physical and environmental drivers of emissions for the majority of BVOC, and 3.) uncertainty in the role of unmeasured and unmodeled compounds from vegetative layers (e.g., understory, midstory, canopy) on the BVOC flux budget. The Flux Closure Study (FluCS) seeks to close these gaps through a uniquely comprehensive characterization of BVOC exchange over a temperate coniferous forest. FluCS applies two high resolution time-of-flight mass spectrometers utilizing H3O+ and I- chemical ionization to simultaneously collect canopy-level fluxes, vertical through-canopy concentration gradients, and needle-level observations across the entirety of two unique mass spectra. Here, we present a first look at some of these measurements that will ultimately be used to quantify the contributions of known and unknown compounds across the mass spectrum to the BVOC flux budget as well as to OH reactivity.