基于MAX-DOAS的淮北地区NO_(2)柱浓度观测研究

MAX-DOAS Observation of NO_(2) Vertical Column Density in Huaibei Area

基于多轴差分吸收光谱技术(MAX-DOAS)反演NO_(2)柱浓度的方法,构建了相应的地基MAX-DOAS系统,开展了NO_(2)柱浓度变化特征的观测。反演中选取天顶方向的光谱作为参考光谱,通过非线性最小二乘法反演出NO_(2)斜柱浓度(SCD),结合不同观测方向的斜柱浓度得到NO_(2)差分斜柱浓度(dSCD),再利用几何近似法得到大气质量因子(AMF),最终获取NO_(2)垂直柱浓度(VCD)。于2019年6月至2020年5月在淮北地区开展了为期一年的外场实验,研究结果表明淮北地区NO_(2)VCD的月均值在观测期间内呈现倒“U”型变化,在12月份达到最高值2.13×10^(16) molecules·cm^(−2),在8月份达到最低值5.23×10^(15) molecules·cm^(−2)。将MAX-DOAS观测结果的日均值与OMI卫星(云系数分别为0<FeC≤0.1和0<FeC≤0.3)测量结果进行对比,发现两者具有较好的相关性(R^(2)=0.88,R^(2)=0.90),表明MAX-DOAS不仅可以准确反演出NO_(2)垂直柱浓度,还可以验证卫星数据。

Based on the method of multi-axis differential optical absorption spectroscopy(MAX-DOAS)retrieval of NO_(2)vertical column density(VCD),the corresponding ground-based MAX-DOAS system was constructed and the variation characteristics of NO_(2)VCD were observed.In the retrieval,the spectrum in the zenith direction was selected as the reference spectrum,and the NO_(2)slant column density(SCD)was retrieved by nonlinear least square method.Combining the slant column density of different observing directions,the NO_(2)differential slant column density(dSCD)was evaluated.Then the air mass factor(AMF)was calculated by the geometric approximation method,and finally the NO_(2)VCD was obtained.A one-year field experiment was carried out in Huaibei area from June 2019 to May 2020.The results showed that the monthly mean value of NO_(2)VCD presents an inverted“U”type change during the observation period,reaching the highest value of 2.13×10^(16) molecules·cm^(−2) in December and the lowest value of 5.23×10^(15) molecules·cm^(−2) in August.Moreover,the daily mean values of MAX-DOAS observations were compared with OMI(0<FeC≤0.1 and 0<FeC≤0.3)measurements,and it is found that the two results had a good agreement(R2=0.88,R2=0.90),which indicates that MAX-DOAS can not only accurately retrieve NO_(2)VCD,but also be used to verify the satellite data.