Dust Aerosols Detected Using A Polarization Lidar And CALIPSO Over Wuhan

Aerosol is the solid and liquid particulate matter that suspended in the atmosphere. It widely exists in the atmosphere, not only affects many atmospheric physics processes, but also directly affects the health and living environment of human beings. Aerosol perticles have important effects on the radiative balance, optics and electricity physics processes, cloud, fog and precipitation of the atmosphere. Over reclamation and grazing cause the water loss and soil erosion and further lead to the emission of dust to the atmosphere. Dust aerosols make great contribution of total atmospheric aerosol loading and Asian dust is one of the most important sources in the earth. In this paper, long-term observations of Asian dust are made using several instruments over Wuhan.Firstly, we introduced the depolarization lidar at Wuhan University and discussed the choice of its key parts and adjustment method. The calculation processes of extinction coefficient, volume depolarization ratio and particle depolarization ratio were detailedly introduced and their error analysis was also made. In addition, other assistant observation instruments were introduced. The depolarization lidar registered 13 dust events between October 2010 and September 2012. The other assistant observation methods, such as CALIPSO, Aura OMI, sun photometer, HYSPLIT model and radiosonde, were also used to fully understand every dust events. The vertical distribution, optical properties, microphysics properties and horizontal range of dust aerosols were obtained.Most dust events occurred in spring (5 events) and winter (6 events). The rest 2 events occurred in summer and fall, respectively. The longest dust event occurred in April 2011 and spaned 9 days, and the depolarization lidar detected the whole events from the beginning to the end. The dust layers mainly occurred at height of approximately 1.4-3.5 km. The horizontal range of the dust plumes were approximately 750-2400 km. The statistical analysis of optical properties showed that the average volume depolarization ratio, particle depolarization ratio, extinction and optical depth of the dust layers were 0.12,0.22,0.19 km"1, and 0.32, respectively.The differences of dust between spring and winter are showed. The dust layers observed in the winter occurred at a lower height and had larger mean extinction and AOD, and smaller mean volume depolarization ratio and particle depolarization ratio than the spring dust layers. The reasons of these differences between the two seasons were further discussed. Lower troposphere temperature inversion usually occurred in winter which restricted the dust aerosols at lower height or even inside the planet boundary layer. As a result, the dust layers were lower and the probability of the mixing of local aerosols and hygroscopic growth under suitable relative humidity conditions was increased in winter. The nonspherical particle shape was suppressed and the extinction coefficient and optical depth were enhanced.Furthermore, compared with the observations at other sites, the dust layers over Wuhan exhibited more turbid along with suppressed nonspherical particle shape. During the southeastward transport process of dust, the velocity of transport was low because it is far away from prevailing westerlies. And the dust plume always went by the large cities with abundant aerosol emission. As a result, aerosols from other sources mixed in the dust layer and changed the primary properties which represented pure dust. This was the reason that caused the different properties of dust over Wuhan from other dust observation sites.