Multi-site Synthesis of the Role of Canopy Processes and Emissions on Ozone and Secondary Organic Aerosols

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The emissions of biogenic volatile organic compounds (BVOCs), such as those from terrestrial vegetation, are known to exert significant control on tropospheric composition and the oxidation capacity of the atmosphere through:(1) their formation of ozone in the presence of reactive nitrogen oxides (NOx = NO + NO2) and sunlight, (2) the regulation of hydrogen oxide radicals (HOx = OH + HO2) and(3) the formation of secondary organic aerosols (SOA) through the transformation of BVOC oxidation products Field campaigns in forested regions continue to improve our understanding of the role of BVOC emissions on gas-phase tropospheric chemistry, yet large uncertainties remain regarding their detailed role in HOx chemistry and SOA formation. A multi-site synthesis is needed to improve understanding of the key physical and chemical processes needed to account for BVOC reactivity. Using a computationally efficient one-dimensional (1D) model, with the ultimate goal of improving regional- and global-scale representation of of BVOCs, researchers from University of Michigan and Washington State hypothesize that many of the HOx mechanism changes recently developed for tropical forests will not achieve the desired model improvement at mid-latitudes. Observations from some five individual US campaigns are to be synthesized in a comprehensive manner and this meta-synthesis is hoped to clarify the role of forests on tropospheric chemistry in moderately clean to polluted regions such as found in the continental US. Since BVOC are also important precursors for short-lived climate forcing agents such a ozone and atmospheric aerosols, improved representation of these species is also needed in future climate models.