Measurement of Water Vapor Absorption in the Ultraviolet Band Using MAX-DOAS and Evaluation of Its Influence on DOAS Retrieval
REN Hong-mei1, 2, LI Ang1*, HU Zhao-kun1, XIE Pin-hua1, 2, 3, XU Jin1, HUANG Ye-yuan1, 2, LI Xiao-mei1, 2, ZHONG Hong-yan1, 4, ZHANG Hai-rong1, 2, TIAN Xin1, 4, REN Bo2, ZHENG Jiang-yi1, 2, WANG Shuai5, CHAI Wen-xuan5
1. Key Laboratory of Environmental Optical and Technology, Anhui Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Hefei 230031, China
2. Science Island Branch of Graduate School, University of Science and Technology of China, Hefei 230026, China
3. CAS Center for Excellence in Urban Atmospheric Environment, Institute of Urban Environment, Chinese Academy of Sciences, Xiamen 361021, China
4. Institutes of Physical Science and Information Technology, Anhui University, Hefei 230601, China
5. State Environmental Protection Key Laboratory of Quality Control in Environmental Monitoring, China National Environment Monitoring Centre, Beijing 100012, China
Abstract:The absorption of atmospheric water vapor gradually weakens from the microwave to the visible band, but the absorption in the ultraviolet band has been ignored. Multi-AXis Differential Optical Absorption Spectroscopy (MAX-DOAS) is a passive optical remote sensing technology that can simultaneously retrieve a variety of trace gases such as NO2, SO2, HCHO, HONO and water vapor. It is often used for regional atmospheric three-dimensional distribution and transportation monitoring, and has the characteristics of low cost, high time resolution stability, and real-time monitoring. Water vapor is an important greenhouse gas, and the water vapor absorption in the ultraviolet band is often not considered when we retrieve trace gases, which may affect the retrieval of trace gases in the ultraviolet band, resulting in systematic errors. This study introduced the atmospheric water vapor retrieval in the ultraviolet band using MAX-DOAS observations in Qianxian, Xi’an, from June 1 to September 24, 2020. The optimal retrieval band in ultraviolet and visible were selected andcompared. The comparison results confirmed the water vapor absorption in the ultraviolet band, and we also evaluated the influence of ultraviolet water vapor absorption on the retrieval of trace gases in the same band. First, the optimal retrieval bands for water vapor in the ultraviolet (351~370 nm) and visible blue bands (434~455 nm) were selected according to the root mean square (RMS) and the absorption cross-sections of H2O and O4. Secondly, the O4 and H2O DSCD in the ultraviolet and visible blue bands were obtained by DOAS fitting, and the correlation between the two bands was analyzed. The two bands’ correlation coefficient of O4 and H2O DSCD in the two bands were 0.85 and 0.80. The ratio of O4 and H2O DSCD in the same band has also been analyzed, and the correlation coefficient in the two bands was 0.89. The high correlation coefficients of H2O DSCD and the ratio of H2O DSCD/O4DSCD in the ultraviolet and visible blue bands indicate that even Xi’an, which has a lower water vapor concentration relative to coastal cities, also has water vapor absorption in the ultraviolet band near 363 nm. It will affect the retrieval of other trace gases in the ultraviolet band using DOAS technology. Finally, the retrieval errors of gases (O4, HONO, and HCHO) that may be affected by water vapor absorption in the ultraviolet band were evaluated. The water vapor absorption in the ultraviolet band will increase O4DSCD, HONO DSCD, and HCHO DSCD during the fitting process, corresponding to the changes of +1.16%, +8.55%, and +9.04%, respectively.
Key words:MAX-DOAS; Ultraviolet band; Water vapor; Error evaluation
任红梅,李 昂,胡肇焜,谢品华,徐 晋,黄业园,李晓梅,钟鸿雁,张海蓉,田 鑫,任 博,郑江一,王 帅,柴文轩. 基于MAX-DOAS测定大气紫外波段水汽的吸收及其对DOAS反演影响的评估[J]. 光谱学与光谱分析, 2022, 42(10): 3314-3320.
REN Hong-mei, LI Ang, HU Zhao-kun, XIE Pin-hua, XU Jin, HUANG Ye-yuan, LI Xiao-mei, ZHONG Hong-yan, ZHANG Hai-rong, TIAN Xin, REN Bo, ZHENG Jiang-yi, WANG Shuai, CHAI Wen-xuan. Measurement of Water Vapor Absorption in the Ultraviolet Band Using MAX-DOAS and Evaluation of Its Influence on DOAS Retrieval. SPECTROSCOPY AND SPECTRAL ANALYSIS, 2022, 42(10): 3314-3320.
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