华北典型污染地区多轴差分吸收光谱技术的气溶胶反演研究

Assessment of MAX-DOAS aerosol retrieval over North China

基于华北典型污染地区的地基多轴差分吸收光谱仪(MAX-DOAS)近4年的观测数据,利用最优估计算法和LIDORT辐射传输模式反演了该区域气溶胶的消光系数垂直廓线和光学厚度(AOD).MAX-DOAS观测反演的AOD与全球气溶胶观测网络同波段在华北地区的AOD间具有很好的一致性,相关系数都在0.9以上,证明MAXDOAS具备对华北污染区域气溶胶光学厚度和消光系数垂直廓线的反演能力.AOD的反演误差表现为冬季最大,春夏最小,早晚大于正午,这是因为冬季以及早晚太阳天顶角较大导致信噪比偏小,所以AOD反演误差偏大.反演廓线表明该区域气溶胶主要集中在1km以下的边界层,浓度随高度呈指数递减,部分情况下峰值出现在300 m处;气溶胶光学厚度夏季最大,冬季最小,正午较大,早晚较小.在东风条件下浓度最高,表明东边(即重工业城市唐山方向)的输送对香河和周边区域的气溶胶积聚有重要贡献.

Based on 4-year MAX-DOAS measurements at the Xianghe Observatory, the aerosol extinction profiles and AODs are retrieved using the optimal estimation algorithm and LIDORT radiative transfer model. The results show a general consistency between the retrieved AODs by MAX DOAS and AERONET product in the same spectral range, with correlation coefficient about 0.9, supporting the capability of MAX-DOAS to derive AOD as well as aerosol extinction profile over North China which suffers enormous air-pollution. The retrieval error tends to be worse in winter-time and morning/evening when the Solar Zenith Angle （SZA） is large, because large SZA induces relatively poor signal to noise ratio and thus large retrieval error. With retrieved aerosol extinction profiles in the Xianghe area, it is found that most of aerosol content is confined within the boundary layer below 1 km with an exponential decay with height. In some cases, however, the aerosol extinction profile peaks at 300 m. With regard to seasonal and diurnal cycles, AOD is higher in mid-day and lower in morning and evening, and annual maximum occurs in summer and minimum in winter. The aerosol loading is heaviest in the case of east wind, suggesting the significant contribution of wind-driven particle transport from Tangshan, a heavy industrial city in North China, to the local accumulation of aerosols in the Xianghe area.