Objective Aerosol plays an important role in assessing radiation, climate, cloud formation, and environmental pollution. In addition, the optical and physical properties of aerosols impact the formation and transmission of air pollutants. Therefore, the temporal and spatial distribution characteristics of tropospheric aerosols are important for studying the uncertainty of the aerosol environment and climate change. It is important to study the optical properties and vertical distribution changes of aerosols through effective observation methods. As a widely used active detection instrument of aerosols, lidar plays an irreplaceable role in the detection of vertical distribution of aerosol and changes in pollutant transmission. Related scholars have researched the distribution characteristics of aerosol extinction coefficient (AEC) and aerosol backscatter coefficient (ABC) profiles, as well as the regional pollution and climate impact by different types of aerosol distribution characteristics, which promotes the development of research methods and lidar detection. High spectral resolution lidar (HSRL) can detect aerosol optical parameters, such as AEC and ABC, enhancing the inversion accuracy of aerosol optical parameters. It provides an efficient method for accurate analysis of climate effects and long-term evolution characteristics of aerosols, as well as the evolution of regional and long-term pollution research.
Methods In this study, the HSRL system based on an iodine molecular filter is used to conduct an aerosol observation experiment in Qinhuangdao in March, 2019. Firstly, the correlation and absolute deviation between the aerosol optical depth (AOD) results retrieved by HSRL system and the data detected by the sunphotometer on the ground site and satellite remote sensor are discussed and analyzed. Combined with the AOD results of HSRL sysytem and ground meteorological data, the optical characteristics and pollution changes of aerosols during the pollution process in the Qinhuangdao area are studied. The distribution of aerosols on a polluted day and the characteristics of stable aerosol layers in cities and ocean areas are studied, and the vertical distribution and particle characteristics of aerosols corresponding to different underlying surfaces are analyzed. ABC, AEC, depolarization ratio (DR), lidar ratio (LR), and color ratio (CR) data are used to analyze the aerosol-concentration distribution and types of aerosol particles at different heights during the pollution process. The study analyzes the changes in aerosol optical parameters and pollutant characteristics during the pollution process.
Results and Discussions According to the comparison results of AOD value, the correlation between the HSRL system and ground-based sunphotometer as well as that between the HSRL system and the satellite remote sensor are more than 0.99 (Fig. 3 and Fig. 4). We use airborne HSRL system to observe the aerosol distribution in Qinhuangdao, and analyze the distribution characteristics of high AOD areas and the changes in AOD at different dates. Combined with the meteorological data and airborne aerosol data, the pollution process in the Qinhuangdao area is analyzed. The pollution process is affected by the southwest wind (Table 3). The airborne observation data are used to analyze the vertical distributions and changes of aerosol parameters corresponding to different underlying surfaces at polluted days. AEC and ABC values on March 4, March 18, and March 19, 2019 are relatively large. The surface layer of the urban area of Qinhuangdao is dominated by industrial pollutants and fine particles produced during biomass combustion. The ABC and AEC values of the low layer decrease with the increase of height. The DR value is below 0.1, the LR value is between 35 sr and 45 sr, and the CR value is between 2.1 and 2.5 (Fig. 7 and Fig. 8); the interaction between aerosol particles in the ocean area leads to the existence of a mixed aerosol layer, including polluted marine aerosols; aerosols in mountain areas are coarse sand and dust. Polluted dust aerosols dominate in some areas, with DR value between 0.1 and 0.18 (Fig. 9).
Conclusions Based on the aerosol data from the HSRL observation experiment, the study analyzes the vertical distribution and pollution characteristics of atmospheric aerosols in Qinhuangdao. We detect the AOD distributions in the east and west regions of Qinhuangdao at different dates, and the AOD observation results are correlated with ground-based and satellite observation data. In addition, we use meteorological data and airborne observation-aerosol data to analyze the boundary-layer changes and vertical distribution of aerosol optical parameters at different dates, and surface types. We observe that the aerosols in the low atmospheric layers of urban areas are mixed aerosols, whereas marine areas are dominated by polluted marine aerosols. The pollutant is a combination of various mixed aerosols. In addition, the types and changes of aerosols under different surface types are different. The pollution is caused by mixed aerosol produced by low-level industries and biomass combustion. The vertical distribution characteristics of three parameters (DR, LR, and CR) that characterized the types of aerosol particles at different dates and altitudes are given. The analysis results of this study reflect the advantages of HSRL system in detecting the vertical distribution of aerosols and regional pollution. Morever, this study provides reference value for the development and application of HSRL system, and supplies a favorable tool for the future development of regional aerosol pollution research.
