基于MAX-DOAS 的淮北地区NO2柱浓度观测研究

基于多轴差分吸收光谱技术 (MAX-DOAS) 反演 NO2 柱浓度的方法, 构建了相应的地基 MAX-DOAS 系统, 开 展了 NO2 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 NO2 斜柱浓度 (SCD), 结合不同观测方向的斜柱浓度得到 NO2 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 NO2 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 NO2 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 2.13×1016 molecules·cm?2, 在 8 月份达到最低值 5.23×1015 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 (R2 = 0.88, R2 = 0.90), 表明 MAX-DOAS 不仅可以准确反演出 NO2 垂直柱浓度, 还可以验证卫星数据。

MAX-DOAS Observation of NO2 Vertical Column Density in Huaibei Area

Based on the method of multi-axis differential optical absorption spectroscopy (MAX-DOAS) retrieval of NO2 vertical column density (VCD), the corresponding ground-based MAX-DOAS system was constructed and the variation characteristics of NO2 VCD were observed. In the retrieval, the spectrum in the zenith direction was selected as the reference spectrum, and the NO2 slant column density (SCD) was retrieved by nonlinear least square method. Combining the slant column density of different observing directions, the NO2 differential slant column density (dSCD) was evaluated. Then the air mass factor (AMF) was calculated by the geometric approximation method, and finally the NO2 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 NO2 VCD presents an inverted “U” type change during the observation period, reaching the highest value of 2.13×1016 molecules·cm?2 in December and the lowest value of 5.23×1015 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 NO2 VCD, but also be used to verify the satellite data.