Testing our Understanding of Biogenic Emissions and their Impacts on Atmospheric Composition above the Amazon Rainforest

Abstract:

Biogenic volatile organic compounds (BVOCs) have a profound effect on atmospheric chemistry and composition, and thereby affect global air quality and climate. The Amazon rainforest constitutes an intense source of BVOCs and is thus a key location in which to probe these effects. Notable uncertainties remain regarding the amount of BVOCs emitted from the rainforest (a function of plant type, environmental conditions and physiological factors) and the quantitative influence they have on atmospheric oxidants, such as OH and O₃ (a function of physical conditions and ambient atmospheric composition, not least the concentration of nitrogen oxides; NO_x=NO+NO₂). The effect that isoprene oxidation at low NO_x concentrations has on the concentrations of OH and O₃ proves a particular challenge to reproduce in atmospheric chemistry-transport models.

We present here the results of a series of experiments aimed at testing our understanding of BVOC emissions from the Brazilian Amazon and the atmospheric chemistry stemming from these. We attempt to reproduce aircraft measurements of BVOCs, NO_x and O₃ from the South American Biomass Burning Analysis (SAMBBA) campaign in 2012, including those made close to the site of recent BVOC emission measurements, just north of Manaus, in the Cooperative LBA Atmospheric Regional Experiment (CLAIRE-UK). We compare the abilities of a variety of atmospheric chemistry mechanisms to capture the measurements in both a global atmospheric chemistry-transport model and a trajectory model of chemistry and transport. The exploration in both Eulerian and Lagrangian frameworks, with their contrasting treatments of mixing, is pertinent in view of: the sensitivity that the chemistry stemming from BVOCs shows to ambient NO_x concentrations; and the episodic influence of anthropogenic emissions in this environment, for example from Manaus.