多轴差分吸收光谱技术测量近地面NO_2体积混合比浓度方法研究

Retrieval of surface NO_2 mixing ratio from multi-axis differential optical absorption spectroscopy

多轴差分吸收光谱技术(MAX-DOAS)通过测量不同角度的太阳散射光,获取痕量气体的柱浓度信息,广泛应用于整层NO2柱浓度的监测.由于缺少有效观测距离的信息,MAX-DOAS无法获取近地面NO2的体积混合比浓度.本文分析了消光系数和有效观测距离的关系,提出了利用能见度信息获取有效观测距离,进而将MAX-DOAS测量的水平方向NO2斜柱浓度转换为体积混合比浓度的方法.并在合肥开展了相应的观测实验,成功实现了基于MAX-DOAS的NO2体积混合比浓度测量.通过与主动式长程差分吸收光谱仪测量的NO2浓度进行对比,结果呈现出较好的一致性,说明了方法的可行性.研究为MAX-DOAS监测近地面NO2体积混合比浓度提供了一种简单有效的方法,拓展了MAX-DOAS的应用领域.

The multi-axis differential optical absorption spectroscopy （MAX-DOAS） technique, in which solar scattered light beams of different elevation angles are used and the spatial distribution of various trace gases is derived, has been widely used for monitoring the NO2 slant column density. Due to the lack of information in a detectable horizontal range of the MAX-DOAS instrument, the concentration of trace gases including NO2 is unable to yield directly. In this work, the relationship between extinction coefficient and light path length of MAX-DOAS observation is analyzed, and a retrieval algorithm to convert the horizontal NO2 differential slant column density into the volume mixing ratio with the information of visibility is described. This algorithm has been used in the MAX-DOAS observation at Hefei, and volume NO2 mixing ratio is derived from MAX-DOAS measurement combining the data of visibility. The NO2 concentration measured with MAX-DOAS shows that it is in good agreement with the result obtained with long path differential optical absorption spectroscopy, proving the feasibility of the retrieval method. This research presents a simple and effective monitoring method of volume NO2 mixing ratio with MAX-DOAS, there by expanding the application scope of MAX-DOAS technique.