基于傅立叶变换红外光谱技术的氨气和硝酸高精度垂直分布的探测研究

Although Reactive ammonia (NH3) and nitric acid (HNO3) are major threats to atmospheric environment and human health, their global and regional distributions, atmospheric processes involved and budget are still poorly known. The technique based on high resolution Fourier transform infrared spectroscopy (FTIR) for remote sensing of vertical distributions of reactive NH3 and HNO3 through the atmosphere has advantages of high sensitivity and high temporal resolution. However, the uncertainty of spectroscopic line parameters leads to the large retrieval errors in vertical profiles of target gases. In addition, the retrieval algorithm based on Optimal Estimation itself has some deficiencies, and it is difficult to determine a priori profile and a covariance matrix for reactive gases which vary significantly in space or time..In this study the method of improving the spectral retrieval strategy and spectroscopic parameters are proposed, including optimizing the forward model and iterative algorithm, in order to reduce the retrieval errors of vertical distributions of atmospheric NH3 and HNO3. The comparison methods between ground-based and satellite remote sensing, atmospheric chemistry transport models are researched. Also, we analyze the spatiotemporal distributions, variation trends and transport characteristics of the two target gases in Hefei region. The research will improve the accuracy, precision and stability of vertical profiles retrieved for reactive gases dramatically, and provide the foundation for revealing spatiotemporal distribution characteristics and variation trends of NH3 and HNO3 in regional atmosphere.

活性气体氨气（NH3）和硝酸（HNO3）是大气环境和人类健康的重大威胁，但目前人们对其全球和区域分布、大气过程和相关收支知之甚少。基于高分辨率傅立叶变换红外光谱（FTIR）技术探测NH3和HNO3整层大气的垂直分布具有高灵敏度、高时间分辨率的优点。然而目前的高光谱反演算法中，光谱线参数的不确定性造成目标气体廓线反演误差较大，基于最优估的反演算法本身也存在不足，并且，对时空变化快的气体构建先验廓线和协方差矩阵是一个难题。.本项目拟针对NH3和HNO3垂直分布反演误差大以及算法本身的不足，提出改进光谱反演策略和光谱线参数的方案，优化前向模型和迭代算法，研究地基FTIR观测与卫星遥感、大气化学传输模型比对的方法，分析大气NH3和HNO3的时空分布、变化趋势和输送特征。本研究将提高活性气体垂直廓线反演的准确性、精度和稳定性，为准确揭示我国区域大气NH3和HNO3的时空分布特征和演变规律奠定基础。

为了理解我国细颗粒物的形成过程，需要在区域和局地尺度上弄清大气氨气和硝酸在颗粒物形成中所起的作用和贡献，因此长期监测大气氨气和硝酸浓度的时空分布和变化是有必要的。本项目采用地基FTIR光谱技术观测合肥地区大气氨气和硝酸的时空分布，并对卫星遥感提供地基验证。基于最优估算法研究大气氨气和硝酸垂直廓线和柱浓度的反演方法，通过改进光谱反演策略和修正光谱线参数来优化反演算法，提高反演的精度；完成了地基遥感和卫星遥感数据比对方法的研究，利用获得的地基遥感数据对卫星遥感进行验证；研究了2017至2020四年内合肥地区大气氨气和硝酸的时空分布和变化规律，分析了浓度变化背后的原因及其与气象参数、气团传输的关系。氨气柱浓度在2017年至2020年显示出增长趋势，四年内氨气柱总量的年均值分别为(1.58±1.02)×1016、(1.83±1.10)×1016、(1.90±1.31)×1016和(1.97±1.00)×1016molec cm-2，年增长速率分别为15.82%、3.83%和3.68%。地表浓度在春夏秋冬四个季节的平均值分别为(7.67±3.99)ppb、(12.93±6.40)ppb、(7.20±3.74)ppb和(4.08±2.66)ppb；地表浓度最大的月均值是7月的15.04ppb，最小的月均值是1月的3.27ppb。氨气柱浓度和地表浓度的月变化表现出高的一致性。分析结果表明，大气温度、风向和源排放是影响合肥氨气浓度变化的主要因素；农业是合肥站点四个季节氨的主要源，而在夏季城市排放源也对站点的高浓度氨气有贡献。四年内大气硝酸平流层偏柱浓度春季最高，秋冬季低，大气整层柱浓度具有相同的季节变化特征。四年内硝酸平流层偏柱浓度逐年下降，年均变化率为-3.0±1.5%。长期的地基观测数据有助于识别合肥地区氨气和硝酸的排放源，为城市大气细颗粒物的减排和防治提供技术支撑和基础数据。