基于多轴差分吸收光谱技术的合肥地区气溶胶观测研究

Aerosol Observation and Research in Hefei by MAX-DOAS Technology

大气气溶胶的直径从几纳米到几十微米不等,对大气辐射评估、全球气候变化、当地空气质量和能见度以及人类健康都有着直接或间接影响,尤其秋冬季节是雾霾高发期,更有利于大气气溶胶的生成、转化和积累。目前,用于气溶胶信息观测的技术有很多,包括激光雷达、太阳光度计、华盖计、卫星遥感等。多轴差分光学吸收光谱(MAX-DOAS)技术是一种被动遥测式光谱设备,具有稳定、可实时连续监测等特点,可同时获取多种痕量气体的浓度信息,且能反演气溶胶光学厚度(AOD)和气溶胶廓线。介绍了MAX-DOAS反演气溶胶信息的算法,并于2017年12月至2018年1月,在合肥市科学岛开展了MAX-DOAS观测,观测方位角为0度(正北),垂直方向上从低到高扫描10个仰角;反演时取中午时段的天顶方向测量光谱作为参考光谱。在337~370 nm波段,利用QDOAS软件计算出O4斜柱浓度(DSCD),然后再利用气溶胶廓线反演算法(PriAM)反演出AOD和气溶胶消光系数(AE)。将结果与太阳光度计CE318测得的AOD做对比,小时均值和日均值的相关性系数均为0.91,结果表明MAX-DOAS在获取气溶胶信息方面具有较高的可靠性。同时,将MAX-DOAS获得的近地面气溶胶消光系数与地面站点的点式仪器测得的PM2.5浓度进行了相关性对比,日均值和小时均值线性拟合相关系数r分别为0.83和0.62,进一步验证了MAX-DOAS获取气溶胶信息的可靠性。由于冬季是雾霾的高发期, AOD值较高,选取2017年12月3日至6日的一次雾霾过程,廓线结果表明气溶胶主要分布在1.5 km以下,结合当时的风场信息及雾霾期间的气流后向轨迹图,可知此次污染是西北方向污染气团输送导致的。

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.