报告学者：Dr. Lei Geng 

学者单位：Department of Atmospheric Sciences at University of Washington 

报告地点：LAPC多功能厅 

报告时间： 2013年12月20日（星期五）上午10:00 

　　Abstract 

　　Tropospheric oxidation capacity, typically defined as the abundance of tropospheric O₃, OH and H₂O₂, determines the lifetimes of trace gases (e.g., CH₄, CO, VOCs) and the production of aerosols (e.g., sulfate, nitrate and secondary organic aerosols) in the troposphere. These gases and aerosols not only affect air quality and human health, but also have climate impact through altering the radiation balance of the atmosphere. Despite the importance of tropospheric oxidation capacity, its response to anthropogenic and climate forcing is still not well-understood. 

　　The chemistry of atmospheric reactive nitrogen, mainly including NO_x (NO + NO₂) and nitrate (HNO₃/NO^3-), is highly coupled with tropospheric oxidation capacity, because 1) the inter-molecular cycling between NO and NO₂ influences the production of O₃ and OH, and 2) the transformation from NO_x to its sink, nitrate, is through oxidation reactions which involve various oxidants but mainly as O₃ and HO_x (OH + HO₂). Thus changes in reactive nitrogen chemistry has implications on the variations in tropospheric oxidation capacity, especially given the fact that the oxygen-17 excess (Δ¹⁷O, the mass independent fractionation signal of stable oxygen isotopes) of nitrate is indicative of the relative abundance of ambient oxidants when nitrate was formed in the atmosphere.  

　　Polar ice sheets preserve atmospheric nitrate expanding back to hundreds of thousands years. In efforts to provide information on the interactions between oxidation capacity and climate change, we investigate past atmospheric reactive nitrogen chemistry by coupling ice core records of nitrate concentration and its stable isotopic composition (δ¹⁵N, Δ¹⁷O) with chemistry-climate modeling. We focus on the preindustrial-present day and glacial-interglacial time scales.