Study Of Anthropogenic Dust Aerosol Based Of CALIPSO Lidar Measurements

Radiation effects of clouds and aerosols has become one of the most uncertain factor in the climate system, and dust aerosols play an important role in the global energy balance, so accurately distinguish between cloud and dust aerosols in the region has a very important significance. But, the existing atmospheric dust load cannot be explained by natural sources alone. The direct solar radiative forcing by anthropogenic dust has a wide range of uncertainty and the forcing by anthropogenically-generated dust aerosols may be comparable to the forcing by other anthropogenic aerosols. Therefore, it is imperative to identify anthropogenic dust and estimate its contribution to mineral dust by observations. Space-borne lidar as an advanced active remote sensing instrument has been widely used in many study, which provide high spatial and temporal resolution, vertical profile and global measurements. Therefore, based on CALIPSO space-borne lidar, related research works with identify anthropogenic dust aerosol will be fully investigated.(1) Validate the accuracy of the CALIPSO cloud and aerosol algorithm. This study discriminated between daytime cloud and dust aerosol over the Sahara Desert in spring 2007 by combining active CALIOP and passive ⅡR measurements (hereafter, CLIM), which was used to solve misclassification of dense dust aerosol. Comparing with simultaneous measurements of CALIPSO, CloudSat, and MODIS, the results revealed that the CLIM dust misclassification rate was 1.16%, much lower than the misclassification rate of CALIPSO Version 2 cloud and aerosol discriminate (hereafter, V2-CAD,16.39%), and lower than that in the Version 3 CAD (V3-CAD, 2.01%). Moreover, the total identification errors were 13.46,3.39, and 1.99% for the V2-CAD, V3-CAD, and CLIM methods, respectively. Thus, the CLIM and CALIPSO V3-CAD method are both significantly better at discriminating between cloud and dust aerosol than the V2-CAD. It could be used as a source of reference data to test other techniques and validate other methods. Meanwhile, it also provides a theoretical basis to identify anthropogenic dust.(2) Planetary boundary layer (PBL) height derived from CALIPSO measurements. In general, horizontal transport of natural dust aerosols occurs mainly above the PBL and only a small amount of this dust enters and remains within the PBL. Therefore, we determine and used PBL height to exclude long-distance transport of dust aerosol from dust sources above the anthropogenic surface described above, so it is important to accurately determine PBL height to separate out the anthropogenic dust. PBL was estimated using the modified maximum standard deviation method for CALIPSO attenuated backscatter observations in this paper. It was only retrieved under conditions where the clouds accounted for less than 5% in a profile, where it could be compared with ground lidar results at SACOL. The correlation between CALIPSO and the ground lidar was 0.73. We present the seasonal mean patterns of 4-year mid-day PBL heights over China and use them to evaluate the European Centre for Medium-Range Weather Forecasts (ECMWF) PBL depth retrievals, inform boundary layer studies, and improve our understanding of how PBL height mediates exchanges of energy and pollutants between the surface and the atmosphere. We found that the largest PBL heights occurred over the Tibetan Plateau and coastal areas. The smallest PBL heights appeared in the Tarim Basin and northeast of China during local winter. A comparison of CALIPSO and ECMWF PBL under different land-cover conditions showed that the PBL depth estimated by the CALIPSO backscatter climatology is larger over oceans and forest surface than that estimated from ECMWF data. However, the PBL heights of ECMWF that were larger than those of CALIPSO were mainly concentrated over grassland and bare land surfaces in spring and summer.(3) Identify anthropogenic dust based on above two studies. To understand the contribution of anthropogenic dust to the total global dust load and its effect on radiative transfer and climate, it is important to identify them from total dust. In this study, a new technique for distinguishing anthropogenic dust from natural dust is proposed by using CALIPSO dust, planetary boundary PBL height retrievals, and optical properties along with a land use dataset. Using this technique, the global distribution of dust is analyzed and the relative contribution of anthropogenic and natural dust sources to regional and global emissions are estimated. Results reveal that local anthropogenic dust aerosol due to human activity, such as agriculture, industrial activity, transportation, and overgrazing, accounts for about 25% of the global continental dust load. Of these anthropogenic dust aerosols, more than 53% come from semi-arid and semi-wet regions. Annual mean anthropogenic dust column burden (DCB) values range from 0.42 g m-2 with a maximum in India to 0.12 g m-2 with a minimum in North America. Considering the mean DCB in four regions, the greatest burden of anthropogenic dust occurs over India and the greatest burden of natural dust occurs over Africa. On a percentage basis, anthropogenic dust is greatest over East China (91.8%) and natural dust over Africa (43.2%). A better understanding of anthropogenic dust emission will enable us to focus on explore the effects of anthropogenic emission on radiative forcing, climate change in the future.