Based on AERONET measurements, aerosol absorption properties over 23 AERONET sites are analyzed. The properties include aerosol single scatter albedo (SSA), correlation characteristic of SSA with aerosol optical thickness (AOT), absorption optical thickness and absorption wavelength index. The index is introduced to indicate wavelength-dependence of absorption optical thickness. Among the 23 sites, 8 sites locate over Asia, 3 over Africa, and 12 in USA. Some results are summarized as follows:
1)Total mean absorption optical thickness for the 440nm-wavelength changes between 0.0061 (Howland, USA) and 0.0939 (Beijing, China), and it ranges from 0.0019 (Howland) to 0.0457 (Yulin, China) for the 1020nm wavelength. There are three peaks of absorption optical thicknesses, locating over China, India and north-Africa, respectively.
2)Over all sites except for two sites (Goa-india in India and Dahkla in Africa), correlative coefficients between SSA and AOT are positive, changing from 0.048 to 0.692. This characteristic implies that relative contribution of stronger-absorbing aerosol component to total AOT decreases when the AOT increases. In other hand, correlative coefficients between Angtr&diaero;m index and AOT are usually negative, showing trendily increasing contribution to total AOT from larger particles when the AOT increases.
3)Apart from two sites of Dahkla and Ilorin in Africa, absorption wavelength index is 0.09-1.29 less than Angtr&diaero;m index, the smallness being larger for some sites in USA. Usually, the larger Angtr&diaero;m index is, the stronger the smallness.
Based on standard Umkehr inversion algorithm the ozone vertical profiles have been retrieved from the Dobson Umkehr observations of Beijing. The corrections are made for aerosols in the process of inversion and the retrieved results have been improved. By using the derived profiles the characteristics and trends of ozone vertical distributions of Beijing during 1990-2002 are studied. The results imply that the ozone concentrations between 10.3 and 23.5km were unusually low during the fall of 1992 and the spring of 1993 and at the same time the total ozone underwent a marked decline. During the period 1990-2002 the total ozone decreased slightly but the trends of change of ozone concentrations at different altitudes were different.
A reasonable cloud screening algorithm is very important to ensure accuracy of aerosol optical thickness determinations from AERONET database. In this paper, a new cloud screening algorithm is developed. The algorithm uses cloud fraction and a so-called scaling height of the tropospheric aerosol, derived from sunphotometer measurements and surface visibility data, to build the screening criterion. The criterion constraints the scaling height varying in some range. In the condition of no cloud day, the variation range is the monthly-mean scaling height plus 3σ (σ: the standard deviation of scaling height). The larger the cloud fraction is, the smaller the range. The new cloud screening algorithm is used to determine aerosol optical thicknesses from AERONET data measured in Beijing during 2001-2002. According to the application results, the reasonableness of the new algorithm is analyzed.
A method is developed to retrieve total Cloud Optical Depth (COD) from broadband Global Solar Radiation detected by paronometer, and available approaches to input aerosol/molecular/gas parameters for the COD retrieval are presented. Aerosol Optical Depth (AOD) retrieved from pyrheliometer data and simultaneous visibility measurement in the clear days are used in building an empirical relationship between AOD and visibility. The relationship is used in determining AOD in the cloudy days. By using the method, the retrieved CODs over 11 meteorological observatories in China during 2001 are compared with MODIS COD products. The difference between the yearly-mean CODs from hourly-accumulated paronometer data and the MODIS COD is less than 34.5% for every site. The agreement between yearly-mean COD from daily GSR data and MODIS COD is also good for all 11 sites except for Geermu site locating over Qinghai-Tibet Plateau. Furthermore, CODs over Beijing and Zhengzhou during 1961-2001 are analyzed.
Two broadband radiation methods are developed to determine aerosol optical depth and the imaginary part of its refractive index. One is broadband extinction method to determine aerosol optical depth by using hourly/daily accumulated pyrheliometer data. Another is broadband solar radiation method to retrieve the aerosol imaginary part from joint pyrheliometer/paranometer data. Furthermore, aerosol optical depths over 11 meteorological observatories in China during 1980-2000, the aerosol imaginary parts and its single scattering albedoes in Beijing and Shenyang during 1993-2000 are retrieved from pyrheliometer/paranometer data by using the methods. Based on the retrieval results, the variation trends of the aerosol optical depths and its imaginary parts, the effects of Pinatubo eruption in 1991, sand-dust event and fossil fuel burning on them are empirically analyzed.
Three lidar systems are developed in Institute of Atmospheric Physics. A four-wavelength lidar is used to detect ozone, aerosol and clouds, which contains a XeCl excimer laser with output energy of about 120mJ at 308nm, a Nd:YAG laser with three operating wavelengths of 355nm, 532nm and 1064nm, and a 1m-receiver telescope. A two-wavelength mobile lidar system is used to detect aerosol in troposphere and Asian dust storm, which has a Nd:YAG laser with wavelengths of 532 and 1064nm. A 1064nm Nd:YAG lidar is used to monitor city aerosol pollution. Since January 2000 the lidar systems have been used in measuring dust storm, high cloud and ground-35km aerosol extinction coefficient profiles. Measurement results show that the aerosol optical depth between 6km and 11km has a mean value of 0.0192; the cloud optical depth between 6km and 11km ranges from 0.014 to 0.23. The aerosol extinction near above the ground changes very greatly. From measurements, the change characteristics of aerosol extinction through snow and rain course, and dust storm are analyzed. Routine city aerosol pollution monitoring result is presented. The results of measurements of ozone shows that during September-October, the maximum ozone concentration is usually in the height range from 25km to 29km, and there is usually second concentration peak in the range between 10km and 17km. The compares of lidar-detected ozone profile made during 20:40-21:35 of October 16, 2001 with balloon measurement during 15:00-16:00 of same day is given.
In this paper, two inversion algorithms considering multiple scattering are proposed to retrieve aerosol/cloud extinction coefficient profiles from LITE data, which are called as the Iterative Forward Integration Algorithm (IFIA) and the Iterative Forward-Backward Integration Algorithm (IFBIA). In IFIA, at first assuming no multiple scattering, retrieve the extinction coefficient profile by the forward integration algorithm. Then, using the profile and assuming an aerosol/ cloud phase scattering function, calculate the multiple scattering component by a parameterized multiple scatter lidar equation (or Monte Carlo calculation) and then yield new extinction coefficient profile solution. By using IRA and IFBIA, some typical LITE data are selected to derive aerosol/cloud extinction coefficient profiles. As shown in the inversion results, if the multiple scattering is neglected, there may be a very large uncertainty in the retrieved aerosol/cloud extinction coefficient profile, especially for the shorter-wavelength 355nm channel and the case of cloud layer. The present algorithms considering multiple scattering can produce more reasonable aerosol/cloud extinction coefficient retrievals.
A backscatter Nd-YAG lidar system has been constructed in our institute, which was designed to measure and image the four- dimensional structure the aerosol and to detect wind in lower atmosphere. It contains a Nd-YAG laser with maximum repetition rate of 15 pulses per second and a 20-cm telescope with maximum field of view of 3 mrad. A fast computer controlled angular scanning system provides can make the lidar to fire at the set position and time. Data logging system provides a logarithmic amplifier of 80 dB, 8 bit A/D conversion with range resolution of 7.5 m and high pixel resolution lidar images in a graphics computer. The system allows observations of inhomogeneities in natural aerosol in boundary layer showing the spatial distribution of aerosol scattering. A model to use triple angle azimuth scan method for measuring wind velocity is developed, which agrees well with the supposed wind in numerical experiment. The lidar system is been used in observations of aerosol and wind in boundary layer during February to July of 1998 and some results are presented.
Some new remote sensing methods of aerosol optical properties and their basic principles are described. The methods are the wide-band extinction method for deriving aerosol optical depth from global direct solar radiation detected by pyroheliometer, the method for retrieving aerosol imaginary index from downward diffuse solar radiation, and the method for deriving aerosol optical depths from joint surface visibility and water vapor pressure. These methods are used to determine aerosol optical depths over 12 meteorological observatories in China during 1980-1994, to retrieve aerosol imaginary index over Beijing and Wulumuqi, and to built aerosol optical depth map in China. Some inversion results are analyzed.