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A rapid method to derive horizontal distributions of trace gases and aerosols near the surface using multi-axis differential optical absorption spectroscopy

机译：利用多轴差分光学吸收光谱法快速推导出地表附近痕量气体和气溶胶水平分布的方法

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We apply a novel experimental procedure for the rapid measurement of theaverage volume mixing ratios (VMRs) and horizontal distributions of tracegases such as NO2, SO2, and HCHO in the boundary layer, which wasrecently suggested by Sinreich et al. (2013). The method is based ontwo-dimensional scanning multi-axis differential optical absorptionspectroscopy (MAX-DOAS). It makes use of two facts (Sinreich et al., 2013):first, the light path for observations at 1° elevation angletraverses mainly air masses located close to the ground (typically < 200 m); second, the light path length can be calculated using thesimultaneous measured absorption of the oxygen dimer O4. Thus, theaverage value of the trace gas VMR in the atmospheric layer between thesurface and the particular altitude, for which this observation was sensitive, can becalculated. Compared to the originally proposed method, we introduce severalimportant modifications and improvements: We apply the method only tomeasurements at 1° elevation angle (besides zenith view), forwhich the uncertainties of the retrieved values of the VMRs and surfaceextinctions are especially small. Using only 1° elevation angle foroff-axis observation also allows an increased temporal resolution. Wedetermine (and apply) correction factors (and their uncertainties) directlyas function of the measured O4 absorption. Finally, the method isextended to trace gases analysed at other wavelengths and also to theretrieval of aerosol extinction. Depending on atmosphericvisibility, the typical uncertainty of the results ranges from about 20%to 30%.We apply the rapid method to observations of a newly-developed ground-basedmultifunctional passive differential optical absorption spectroscopy(GM-DOAS) instrument in the north-west outskirts near Hefei in China.We report NO2, SO2, and HCHO VMRs and aerosol extinction for fourazimuth angles and compare these results with those from simultaneouslong-path DOAS observations. Good agreement is found (squares of thecorrelation coefficients for NO2, SO2, and HCHO were 0.92, 0.85,and 0.60, respectively), verifying the reliability of this novel method.Similar agreement is found for the comparison of the aerosol extinction withresults from visibility meters. Future studies may conduct measurementsusing a larger number of azimuth angles to increase the spatial resolution.
机译：我们应用了一种新颖的实验程序来快速测量边界中痕量气体（如NO 2 ，SO 2 和HCHO）的平均体积混合比（VMR）和水平分布层，最近由Sinreich等人提出。 （2013）。该方法基于二维扫描多轴差分光学吸收光谱法（MAX-DOAS）。它利用了两个事实（Sinreich等人，2013）：首先，以1°仰角进行观测的光路主要穿过靠近地面（通常<200 m）的气团。其次，可以通过同时测量氧气二聚体O 4 的吸收来计算光程长度。因此，可以计算该观测值敏感的表面和特定高度之间的大气层中痕量气体VMR的平均值。与最初提出的方法相比，我们引入了一些重要的修改和改进：我们仅将该方法应用于仰角为1°的测量（除天顶视图之外），因此VMR和表面消光的取回值的不确定性特别小。仅使用1°仰角进行离轴观测也可以提高时间分辨率。直接确定（并应用）校正因子（及其不确定性）作为所测O 4 吸收的函数。最终，该方法扩展到了在其他波长下分析的痕量气体，并且还解决了气溶胶的消光问题。根据大气可见性，结果的典型不确定性范围约为20％至30％。 我们将快速方法应用于新开发的基于地面的多功能无源差分吸收光谱仪（GM-DOAS）的观测我们报告了NO 2 ，SO 2 和HCHO VMR和四方位角气溶胶消光的结果，并将这些结果与来自同时进行长途DOAS观测。发现良好的一致性（NO 2 ，SO 2 和HCHO的相关系数的平方分别为0.92、0.85和0.60），证明了该方法的可靠性对于气溶胶的消光与能见度仪的结果的比较，发现了相似的协议。未来的研究可能会使用更多的方位角进行测量，以提高空间分辨率。

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