基于OP-TDLAS激光远程探测的秸秆堆肥农田面源氨排放特征研究

Due to the change of soil physical and chemical properties, the risk of non-point source ammonia emission is increased. At present, the measured data of ammonia emission coefficient of straw compost in China are not enough, and the traditional ventilation method or vorticity method only provide local small-scale results which are difficult to reflect the complete spatial and temporal characteristics of non-point source. In view of the urgent requirements for the preparation of ammonia emission inventory in China, this project combines OP-TDLAS laser remote detection and vertical radiation plume map (VPRM) technology to study the characteristics of ammonia emission from non-point source.. By analyzing the influence of atmospheric turbulence and environmental parameters on the open-path spectrum measurement, the characteristic spectrum detection and analysis are achieved by designing the co-frequency and dual-wavelength working mode to calculate the path integral concentration accurately. The fusion method of laser remote detection concentration and micrometeorology data is studied and the ammonia emission rate is retrieved by VRPM model. The effects of transmission path, observation height, networking mode and grid division on flux measurement are explored through preliminary experiments, also the working parameters are optimized. A typical straw compost farmland is selected for long-term continuous observation to obtain flux monitoring results with high time resolution, clarify the emission law of the same non-point source in different seasons and different meteorological conditions and improve the accuracy of flux measurement. This method provides technical support for accurately obtaining the ammonia emission characteristics of non-point source and improving the emission inventory of agricultural source ammonia in China.

由于农田秸秆堆肥方式改变了土壤理化性质，增加了面源氨排放的风险。目前我国秸秆堆肥氨排放系数的实测数据缺乏，而传统通气法或涡度法仅提供局地小尺度结果，难以反映出面源完整的时空特征。针对我国氨源排放清单编制的迫切要求，本项目结合OP-TDLAS激光远程探测和垂直辐射羽流图（VPRM）技术，研究面源氨排放特征。.通过分析大气湍流以及环境参数对开放光谱测量的影响，设计同频双波工作方式进行特征光谱探测及解析，精确计算路径积分浓度；研究激光远程探测浓度和微气象学数据的融合方法并通过VRPM模型反演氨排放率；通过初步实验探索传输光程、观测高度，组网方式和网格划分对通量测量的影响，优化工作参数；选择典型秸秆堆肥农田进行长期连续观测，获得高时间分辨率通量监测结果，明晰同一面源在不同季节、不同气象条件下的排放规律，提高排放通量测量的准确度。本方法为准确获取面源氨排放特征，完善我国农业源氨排放清单提供技术支撑。

我国农田秸秆堆肥方法对面源氨排放的目前缺乏长期观测方法及数据，传统通气法或涡度法仅提供局地小尺度结果，难以反映出面源完整的时空特征。因此本项目重点设计扫描型开放激光探测系统和光谱解析方法，优化基于激光远程探测（OP-TDLAS）和垂直辐射羽流图（VRPM）的面源排放测量方法，获得了典型旱地作物秸秆堆肥面源的高时间分辨率氨排放特征，本方法为准确获取面源氨排放信息，完善我国农业源氨排放清单提供技术支撑。.（1）OP-TDLAS系统结合用于扫描吸收光谱的激光波长锁定方法，利用同频双波工作方式进行特征光谱解析，并设计了浓度反演算法有效获取路径积分浓度，提高了外场环境下氨气测量的稳定性，改进方法修正后数据标准差为0.127，比传统方法提高2.63倍；通过压力伺服控制技术获得高分辨氨气中红外混叠光谱特征信息。.（2）基于S型控制算法实现扫描型OP-TDLAS系统二维旋转精确定位，通过优化基函数、改进SSE最小化函数、通过加权方法和历史数据修正当前积分浓度改进了VRPM平滑基础函数最小化（SBFM）重建方法和反演算法，并通过优化仪器工作参数（最佳平均数据周期，传输光程、观测位置、观测高度差、组网方式）、数据质量控制和分析复合面源贡献系数提高排放测量的有效性。.（3）获得黄淮海平原典型旱地作物秸秆堆肥氨排放连续观测结果，夏季的氨挥发速率高于秋冬季；氨挥发呈明显的日变化趋势，随温度升高而排放增加；秸秆堆肥和施肥均促进土壤氨挥发，施肥的增势效果更为快速，在施肥后一周时间内排放明显上升；堆肥还田对氨挥发效果表征时间更久，在还田1个多月后氨挥发上升。施肥期夏季氨挥发最大值为20.13 kg N/(hm2 d)，秋季为17.23 kg N/(hm2 d)，长期秸秆还田后的氨排放峰值为6.64 kg N/(hm2 d)。