应用多光路主动差分光学吸收光谱仪观测大气污染物的空间分布

Observation on the spatial distribution of air pollutants by active multi-axis differential optical absorption spectroscopy

研制了一套具有4条测量光路的主动差分光学吸收光谱仪(DOAS)系统,以一盏短孤氙灯为4台集成一体的发射/接收望远镜提供光源,可同时发射4条相互独立的测量光路,4台望远镜的角度可分别独立调整以对准不同位置的角反射镜,光路之间的最大发散角可达28°.为测试仪器性能,使4条光路测量同一区域内的NO2浓度.对4条光路的测量结果进行相互对比,任意两条光路的相关系数均在0.97以上,测得NO2的体积分数平均差异小于10-9,表明结果具有良好的一致性.通过对复旦大学附近区域内的NO2,SO2垂直分布进行长期连续观测,获得了观测区域内两种污染物垂直分布的平均日变化特征:NO2浓度为双峰变化,两个高峰分别出现在早晨和傍晚,低谷出现在午后和凌晨,在垂直方向上,44—66m高度层浓度最高,66—88m高度层浓度最低,浓度的层间差异夜间高于白天,最大差异达17×10-9;SO2浓度为单峰变化,峰值出现在上午,垂直分布相对均匀,层间差异最多不超过3×10-9.

An active 4-axis differential optical absorption spectroscopy system is developed in the project. The system has 4 telescopes integrated together that can simultaneously project and receive 4 independent light beams for measurement. The 4 beams share one xenon short-arc lamp as the light source. Each telescope can be adjusted individually to point to different reflectors. The angle between different beams can be adjusted up to 28°. A test is conducted on the system with four beams setting to measure the concentration of NO2 in the same area. The comparison shows good consistency between measurement data from different beams： the correlation coefficient （R2） between the data from any two beams is no less than 0.97 and the average difference between different beams is below 1×10^-9. The long-term observations on the vertical distributions of NO2 and SO2 around Fudan University reveal the average feature of its daily variation： the concentration of NO2 shows a variation of double-peak in a day, the 2 peaks occur in the early morning and the evening respectively, while the valleys occur in the afternoon and the wee hours; the layer of 44—66 m has the highest NO2 concentration, while the layer of 66—88 m the lowest; during the nighttime, inter-layer difference of NO2 concentration is higher than that during the daytime and can be as high as 17×10^-9; the concentration of SO2 shows a variation of single-peak in a day, the peak occurs in the forenoon; the vertical distribution of SO2 is relatively even, with the inter-layer difference below 3×10^-9.