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Please use this identifier to cite or link to this item: http://hdl.handle.net/2031/5460

Title: Studies of urban atmospheric aerosols using lidar and sky radiometer
Other Titles: Ji guang lei da ji tian kong fu she ji dui cheng shi da qi qi rong jiao zhi yan jiu
激光雷達及天空輻射計對城市大氣氣溶膠之研究
Authors: Yang, Xun (楊勳)
Department: Department of Physics and Materials Science
Degree: Master of Philosophy
Issue Date: 2008
Publisher: City University of Hong Kong
Subjects: Atmospheric aerosols.
Optical radar.
Radiometers.
Notes: CityU Call Number: QC882.42 .Y36 2008
xv, 121 leaves : ill. 30 cm.
Thesis (M.Phil.)--City University of Hong Kong, 2008.
Includes bibliographical references (leaves 110-121)
Type: thesis
Abstract: This thesis discusses the remote sensing of atmospheric aerosols, the corresponding instrumental technology and inversion algorithm. The urban aerosol optical properties in Hong Kong have been studied by using a micro-pulse lidar (Light Detection and Ranging) and a sky radiometer. The long-term change of aerosol and its correlation to synoptic condition have been analyzed. Corresponding instrumental technology has been investigated. In chapter 2, the methodologies of active and passive remote sensing of atmospheric aerosols have been reviewed. It covers the following: (2.1) the Earth’s atmosphere structure and aerosols. The structure of boundary layer and its relationship to aerosols are introduced. The importance of atmospheric aerosol and corresponding measuring methods are discussed; (2.2) active remote sensing by lidar and corresponding laser profiling technology. A review of lidar technology for atmosphere and aerosol study is presented; the principle of micro-pulse lidar for sensing aerosols and the boundary layer is discussed; (2.3) introduction of passive remote sensing from ground-based and satellite systems. In chapter 3, the mechanic scanning methods to profile laser beam, the lidar light source, are described. This chapter includes: (3.1) the importance of laser profiling to guarantee laser quality for lidar system and a review of three profiling methods, the knife-edge scanning, the pinhole scanning and the slit scanning. Furthermore, the principle of the second moment measurement is discussed; (3.2) error sources and propagation in profiling, where different instrumental error sources This thesis discusses the remote sensing of atmospheric aerosols, the corresponding instrumental technology and inversion algorithm. The urban aerosol optical properties in Hong Kong have been studied by using a micro-pulse lidar (Light Detection and Ranging) and a sky radiometer. The long-term change of aerosol and its correlation to synoptic condition have been analyzed. Corresponding instrumental technology has been investigated. In chapter 2, the methodologies of active and passive remote sensing of atmospheric aerosols have been reviewed. It covers the following: (2.1) the Earth’s atmosphere structure and aerosols. The structure of boundary layer and its relationship to aerosols are introduced. The importance of atmospheric aerosol and corresponding measuring methods are discussed; (2.2) active remote sensing by lidar and corresponding laser profiling technology. A review of lidar technology for atmosphere and aerosol study is presented; the principle of micro-pulse lidar for sensing aerosols and the boundary layer is discussed; (2.3) introduction of passive remote sensing from ground-based and satellite systems. In chapter 3, the mechanic scanning methods to profile laser beam, the lidar light source, are described. This chapter includes: (3.1) the importance of laser profiling to guarantee laser quality for lidar system and a review of three profiling methods, the knife-edge scanning, the pinhole scanning and the slit scanning. Furthermore, the principle of the second moment measurement is discussed; (3.2) error sources and propagation in profiling, where different instrumental error sources chapter includes: (4.1) a detailed description of the system specifications; (4.2) instrumental technology including the software control, system corrections and maintenance; (4.3) investigation of vertical aerosol and the boundary layer based on the long-term observations from January to June in the year of 2006. The vertical aerosol profile has been studied. The monthly mean aerosol extinction profiles show different patterns, where a gradually decreasing-extinction along the increasing height is found in January, February and April and high extinction values beyond 0.5 km has been found in April, May and June. The monthly mean boundary layer is observed to increase gradually since January (0.55 km) and reach to the maximum in March (0.63 km) and has the lowest value in April (0.46 km). The diurnal boundary layer height is found to be generally higher than that in the evening. The monthly mean aerosol optical thicknesses (AOT) from the lidar, AERONET and MODIS have been compared. The monthly evolutions show similar change with maximum values appearing in March. In each month, the aerosol optical thickness from AERONET generally has the highest value while the lidar retrieved one is of the lowest value. Corresponding meteorological conditions such as the temperature, relative humidity, respirable suspended particulate (RSP), visibility and wind have been combined for analysis. The monthly RSP concentration coincides with retrieved aerosol optical thickness, which has the similar evolution also found to appear in. This agrees with the monthly AOT change. Moreover the monthly RSP has the similar evolution as AOT with highest value appeared in March (74.9 μg/m3) and lowest value in June (30.7 μg/m3). By contrast, the monthly visibility has the smallest value in March. The wind speed is found to be accompanied with low RSP concentrations. Furthermore, it is found that the wind from the north, the mainland of China, generally corresponds to high RSP concentrations, while the southern wind is with low RSP concentrations. Correlation analysis has bee performed between different data at the same time. The AOT values from lidar and the AOT from AERONET at different wavelengths show a linear correlation with mean R2 of 0.4, where the AERONET AOT is larger. The AOT data from MODIS of Terra and the lidar AOT has a linear correlation with R2 of 0.48, where the AOTs from MODIS are larger. The mean extinction coefficients retrieved from lidar are found to be positive correlation (a R2 of 0.56) with ground-measured RSP concentrations. A R2 of 0.35 is found between the extinction and visibility. The passive remote sensing of aerosol features by using a sky radiometer has been presented in chapter 5 that includes: (5.1) the introduction of the system specifications; (5.2) study of the retrieved columnar aerosol optical thickness at five wavelengths, 400, 500, 675, 870 and 1020 nm, from the year of 2002 to 2004. The monthly average values of AOT in the afternoon are generally larger than those in the morning. In an annual view, the monthly mean AOT generally has two peaks appearing in late spring (around March and April) and autumn (around September and October), while lower AOT values usually occur in middle-summer (around June) and winter (around November). The annual mean AOTs at shorter wavelength channels have larger increasing percentage than those at longer wavelength channels, where the AOT at 400 nm has increased by 33% from 0.641 in 2002 to 0.854 in 2004, whilst a 22% increasing from 0.565 to 0.687 is found at the 500 nm. There are no significant changes for the near infrared channels at 870 and 1020 nm. (5.3) correlation analysis between aerosol properties retrieved from the sky radiometer and local synoptic conditions as well as the backward trajectory analysis. Both AOT and RSP in the afternoon are found to be of higher values than those in the morning. The monthly mean RSP concentrations are found to have similar change. High wind speed is found to be more likely to result in small AOT and RSP concentrations. The main direction of trajectories has regular annual change, which turns from north in January to east in April and turn to the south in June and July. Then it turns back to east again after August and again northern trajectories dominate at the end of the year. The yearly northern trajectories have farthest source distances, while the southern trajectories have shortest source distances. The source distances are relatively shorter around April and September and are longer around June and January. Backward trajectories have relationship with the AOT, where the northern trajectories is found to usually correspond to higher AOTs as well as higher RSP concentrations, indicating possible aerosol transport from mainland of China to Hong Kong. The southern trajectories prevail in June corresponding to a low AOT. To sum up, a comprehensive study on local atmospheric aerosols has been performed using remote sensing technology and theoretically analyses. It is expected that the active and passive remote sensing technology on observing local atmospheric aerosols will provide an important basis on understanding atmospheric environment and aerosol impact and promise exciting opportunities to improve the research of studying atmospheric aerosols. Furthermore the development of corresponding instrumental techniques like the laser profiling and lidar systems is expected to boost corresponding experimental technology and measurement accuracy.
Online Catalog Link: http://lib.cityu.edu.hk/record=b2340604
Appears in Collections:AP - Master of Philosophy

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