Aerosol Observation and Research in Hefei by MAX-DOAS Technology
LI Xiao-mei1, 2, XIE Pin-hua1, 2, 3*, XU Jin1, LI Ang1, TIAN Xin2, REN Bo2, HU Zhao-kun1, 2, WU Zi-yang2
1. Key Laboratory of Environmental Optical and Technology, Anhui Institute of Optics and Fine Mechanies, Chinese Academy of Sciences, Hefei 230031, China
2. Science Island, 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
Abstract：Atmospheric aerosols range in diameter from a few nanometers to tens of micrometers, with direct or indirect effects on atmospheric radiation assessments, global climate change, local air quality and visibility, and human health. Especially during the high season of smog in autumn and winter, it’s more conducive to the formation, transformation and accumulation of atmospheric aerosols. At present, there are many technologies for aerosol observation, including laser radar, solar photometer, canopy meter, and satellite remote sensing, etc. Multi-axis differential optical absorption spectroscopy (MAX-DOAS) technology is a passive and telemetry spectroscopy instrument. In addition to the characteristics of stable and real-time continuous monitoring, it can simultaneously acquire the concentration information of various trace gases and further retrieve the aerosol optical thickness (AOD) and aerosol profile. This paper introduces the method of aerosol retrieval by retrieving O4 column concentration information based on MAX-DOAS technology. Ground-based MAX-DOAS measurements were carried out at Science Island, Hefei from December 2017 to January 2018. The spectra were recorded with an azimuth of 0 degrees (north) and 10 elevation angles from low to high in the vertical direction for each scanning cycle. The zenith direction measured the spectrum as a reference spectrum. In the 337～370 nm band, we calculated the total amount of oxygen dimer (O4) differential slant column densities (DSCD) using QDOAS software, and retrieved aerosol optical thickness (AOD) and aerosol extinction coefficient (AE) using the aerosol profile inversion algorithm (PriAM). We compared the results with the AOD measured by the solar photometer CE318, and the correlation coefficient between the hourly mean and the daily average was 0.91. The results showed that MAX-DOAS has high reliability in obtaining aerosol information. In addition, we also compared the near-surface aerosol extinction coefficient obtained by MAX-DOAS with the PM2.5 concentration measured by the point instrument at the ground station. The correlation coefficient r of the daily mean and hourly mean linear fit was 0.83 and 0.62, respectively, which further verified the reliability of MAX-DOAS for obtaining aerosol information. Since winter is a time for high incidence of haze, the AOD value is higher. We studied a smog process from December 3 to 6, 2017, and found the aerosol was mainly distributed below 1 km. Combining with the wind field information and the airflow backward trajectory map during the period of haze, it can be seen that the pollution is caused by the transportation of polluted air masses in the northwest.
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