华北农村区域夏季大气中异戊二烯未知来源的探究

As an important volatile organic compound emitted from plant species, isoprene has been shown to be the precursor of SOA and ozone, and have an important impact on regional and global environment. Base on the abnormal phenomenon of the peak concentration of atmospheric isoprene (3-4 ppbv) at dusk obtained both from the study group of the applicant and the Peking university, we suggest that maize is the main atmospheric isoprene source in the study site and have obviously different emission characteristics with trees. And hence, with the maize (planted in the Wangdu County, Hebei province) as the study object, the exchange fluxes and the emission characteristics of isoprene at different growth stages are obtained by using dynamic chambers, which would be used to explain the abnormal phenomenon of the diurnal variation of atmospheric isoprene. Simultaneous recording of the photosynthetically active radiation and the temperature in the dynamic chamber to seek the quantitative relation between the isoprene emission and these impact factors, and simultaneous determination the exchange fluxes of carbon dioxide to reveal the relationship between the isoprene emission and the unphotosynthetic. Finally, based on the obtained isoprene emission fluxes, we estimate the total isoprene emissions from maize.

植物排放的异戊二烯是大气中一种重要的挥发性有机物，是二次有机气溶胶及臭氧的重要前体物，对区域乃至全球环境具有重要的影响。申请者基于所在课题组及北京大学在华北农村站点玉米季均观测到大气中异戊二烯傍晚峰值（3-4ppbv）的异常现象，推测玉米作物是大气异戊二烯的主要来源，且其排放特征与树木异戊二烯的常规排放特征可能显著不同。为此，本项目拟选择河北省望都县东白陀玉米作物为研究对象，采用双动态箱法测量玉米整个生长季节异戊二烯的排放通量，获得玉米不同生长阶段异戊二烯排放的日变化特征，阐明农村观测站点大气中异戊二烯异常日变化特征的原因；同步测定箱体内光合有效辐射及温度，探寻玉米作物异戊二烯排放量与它们之间的定量关系；同步测定二氧化碳的交换通量，揭示玉米光合休眠期与玉米作物异戊二烯排放通量的关系；基于所测异戊二烯的排放通量，估算华北玉米作物异戊二烯的排放总量。

植物排放的异戊二烯是大气中一种重要的挥发性有机物，是二次有机气溶胶(SOA)及臭氧(O3)的重要前体物，对区域乃至全球环境具有重要的影响。申请者基于所在课题组及北京大学在华北农村站点玉米季均观测到大气中异戊二烯傍晚峰值（3-4ppbv）的异常现象，推测玉米作物是大气异戊二烯的主要来源，且其排放特征与树木异戊二烯的常规排放特征可能显著不同。为此，本项目选择河北省望都县玉米作物和法桐树木为研究对象，采用双动态箱法测量其异戊二烯的排放通量。研究发现玉米不同生长阶段异戊二烯排放可以忽略，表明玉米作物排放异戊二烯对区域环境的影响较弱。玉米作物在一定生长阶段对大气OVOCs和臭氧具有显著的吸收作用，大面积玉米的种植对缓解华北平原地区夏季大气臭氧污染具有积极作用。法桐树叶呈现异戊二烯的高排放特征，其异戊二烯排放通量峰值达80mg m-2 h-1，且与光照正相关。不同生长阶段的梧桐树叶对大气OVOCs和臭氧的作用并不相同，即生长活力强的法桐树叶对大气臭氧和OVOCs具有吸收作用，而生长活力差的法桐树叶对臭氧的吸收作用较弱，并对甲醛、乙醛和丙酮等OVOCs呈现显著的排放特征。结合北京、泰安及河北望都外场大气异戊二烯的加强观测研究，揭示了华北农村地区异戊二烯在傍晚出现典型峰值的原因主要归属于大气氧化性的变化。本项目的研究结果揭示了华北农村大气异戊二烯的来源及变化特征，为深入评价该地区大气异戊二烯对区域环境的影响提供重要技术支撑。