Biosphere-atmosphere chemical interactions during drought and heat waves in dryland ecosystems Prof. Alex Guenther University of. California, Irvine, USA

Biogenic volatile organic compounds (BVOC) are produced by terrestrial ecosystems and emitted into the atmosphere where they participate in chemical reactions that determine the atmospheric distributions of air pollutants and short-lived climate forcers including organic aerosol, ozone and methane. BVOC are the dominant global emission of reactive organics into the atmosphere and are included in most air quality and climate models with simple representations that broadly describe the observed behavior under optimal ecological conditions. It is well known BVOC emissions are sensitive to abiotic (e.g., drought and heat waves) and biotic (e.g., herbivores and microbes) stresses but these processes are difficult to quantify and are currently either omitted or highly simplified in numerical models. We assess the role of BVOC in biosphere-atmosphere chemical interactions during drought and heat waves in dryland ecosystems by synthesizing observations from Yatir forest and other field sties with laboratory investigations of drought and heat stress-induced BVOC emission and incorporating the results into the BVOC emission component of a regional chemistry and transport model. Model simulations using the MEGAN BVOC emission model embedded in the WRF-Chem chemistry and transport model are used to investigate the impact of drought and heat stress induced BVOC emission on atmospheric chemical composition and determine the potential for significant interactions and feedbacks. MEGAN simulations with and without stress are used to quantify the potential sensitivity of BVOC emission response. WRF-Chem regional model simulations are used to demonstrate how the stress-induced changes can influence atmospheric chemistry and ecosystem functioning to assess potential interactions and feedbacks.