Ethene, propene, butene and isoprene emissions from a ponderosa pine forest measured by relaxed eddy accumulation

摘要

Alkenes are reactive hydrocarbons that influence local andregional atmospheric chemistry by playing important roles in the photochemicalproduction of tropospheric ozone and in the formation of secondary organicaerosols. The simplest alkene, ethene (ethylene), is a major plant hormoneand ripening agent for agricultural commodities. The group of light alkenes(C-C) originates from both biogenic and anthropogenic sources,but their biogenic sources are poorly characterized, with limited field-basedflux observations. Here we report net ecosystem fluxes of light alkenes andisoprene from a semiarid ponderosa pine forest in the Rocky Mountains ofColorado, USA using the relaxed eddy accumulation (REA) technique during thesummer of 2014. Ethene, propene, butene and isoprene emissions have strongdiurnal cycles, with median daytime fluxes of 123, 95, 39 and17 µg m h, respectively. The fluxes were correlatedwith each other, followed general ecosystem trends of CO and watervapor, and showed similar sunlight and temperature response curves as otherbiogenic VOCs. The May through October flux, based on measurements andmodeling, averaged 62, 52, 24 and 18 µg m h forethene, propene, butene and isoprene, respectively. The light alkenescontribute significantly to the overall biogenic source of reactivehydrocarbons: roughly 18 % of the dominant biogenic VOC,2-methyl-3-buten-2-ol. The measured ecosystem scale fluxes are 40–80 %larger than estimates used for global emissions models for this type ofecosystem.