基于涡动相关法观测求得农田一氧化氮排放通量的方法探索

Terrestrial ecosystems in rural regions are the major sources of atmospheric nitric oxide (NO), which is an important atmospheric pollutant itself and an essential precursor of a number of atmospheric pollutants. It is strongly expected to accurately quantify NO effluxes from terrestrial ecosystems on the basis of measurement using an eddy covariance technique (EC). As the gas is a reactive species, however, an EC-measured NO flux over an ecosystem, even in a rural region, is usually not representative directly for the NO efflux from the land surface, due to atmospheric chemical consumption of NO by reaction, e.g., primarily with ozone at daytime. Following the principle of mass conservation for the NO at the position of the EC sensor, the chemical reaction kinetics between atmospheric NO and ozone and, the lately revised equation for the classic hole-in-the-pipe model on NO and N2O emissions, this project will attempt to establish a function to describe the dependence of an EC flux of NO jointly upon land surface efflux of N2O, atmospheric concentrations of NO and ozone, air temperature, soil temperature and, soil concentrations of ammonium and nitrate. This function is expected to apply at daytime for rural upland ecosystems with non-forest vegetation. Parameters of this function are to be estimated using simultaneously measured data of the involved variables, and then to be used to calculate the divergence of an EC flux from the corresponding surface efflux. Using the divergence value to correct the EC flux, subsequently, the surface efflux of NO is determined. This attempt is expected to success so as to establish a brand new approach for determining daytime NO effluxes from rural upland ecosystems with non-forest vegetation based on EC measurement of NO fluxes and simultaneous observation of the other relating variables.

陆地生态系统是乡村地区向大气输入一氧化氮（NO）的主要排放源，因而依托涡动相关法（EC）测量来准确定量生态系统尺度的NO排放通量具有重要科学意义。但在大气中，NO是反应性气体，致使EC测量结果对白天乡村低矮植被生态系统NO排放通量的代表性，主要取决于大气中NO被臭氧消耗的程度。项目拟针对低矮植被旱地生态系统的白天时段，根据EC观测位置的大气NO质量守恒，大气中NO被臭氧消耗的化学反应，以及关于土壤氧化亚氮和NO排放的“管孔泄漏”模型改进型方程，建立EC测量的NO通量随氧化亚氮通量、大气NO和臭氧浓度、气温、土壤温度和土壤水分含量以及土壤铵态氮和硝态氮含量而变化的关系式，通过多变量同步观测估计关系式的参数，用以求算EC测量的NO通量相对于地面NO排放通量的偏移值，进而求得地面排放NO的通量。这项探索旨在建立依托EC观测及相关变量同步测量定量低矮作物生态系统NO排放通量的一套全新方法。

陆地生态系统是乡村地区向大气输入一氧化氮（NO）的主要排放源，因而依托涡动相关法（EC）测量来准确定量生态系统尺度的NO排放通量具有重要科学意义。但在大气中，NO是反应性气体，致使EC测量结果对白天乡村低矮植被生态系统NO排放通量的代表性，主要取决于大气中NO被臭氧消耗的程度。为解决这一问题，本项目自主研发了一套可同步高频测量七种气态物质（包含NO）地气交换通量的EC法观测系统，应用该系统，开展了低矮植被旱地生态系统NO地气交换通量观测研究。根据NO气体从地表被湍流输送至EC仪器所在位置过程中的质量守恒，以及大气中NO被臭氧消耗的化学反应，对白天时段获得的NO浓度10Hz观测值进行臭氧反应所致误差的修正方案，再用于EC法计算NO通量，其结果代表地面的NO排放通量，修正后的NO通量比EC法直接获取的通量高63%。这项探索成功建立了依托EC观测及相关变量同步测量定量低矮作物生态系统NO排放通量的一套全新方法。基于上述观测设备和方法，成功获得第一套NO和N2O通量的涡动相关法同步观测数据集，揭示了亚热带典型施肥农田NO和N2O排放通量的变化特征及其控制因素。