Comprehensive Observation Of Dust Aerosol Over Loess Plateau

Local and global responses of climate change to the aerosol depend strongly on its optical and physical properties.Aerosol is very effective in modifying the radiation field by absorbing and scattering solar and thermal radiation strongly modify the radiation budget at the surface of the earth as well as the cloud microphysical properties,precipitation rate and hydrological cycle. In recent years,blace carbon(BC)became more and more important because of its direct impace on radiation and its heating effect on climate,Additionally,BC can affect the climate by its indirect effects due to its action on cloud droplet and change the cloud proerties.China loess Plateau and the deserts in the arid and semi-arid regions of Northwest China are considered as the largest and most persistent dust sources and air pollution in the Northern Hemisphere However, due to the shortage of in situ observations in those regions,the detailed information on their physical and optical properties of dust and non-dust aerosol from those regions have not been well understood yet.Understandings on physical processes and its optical propertities of aerosols are important because atmospheric aerosols play key roles to affect the earth-atmosphere radiative system.The main objective of this paper is to identify detailed information of aerosol measurements conducted over China loess Plateau.The conclusions can be summarized as follows:(1)In order to examine the decadal variations of the dust events over East Asia,we analyze surface observations from 701 meteorological stations for the period 1960-2004 to obtain spatial and temporal distributions of dust events.Since the Taklamakan Desert in western China and the Gobi Desert in Inner Mongolia are the two major sources of dust storms,we have defined two dust indices,one for the Taklamakan Desert Index(TDI)and one for the Gobi Desert Index(GDI), tocharacterize the statistical nature of the dust events over these two regions.Both of these indices are well correlated with the Total Ozone Mapping Spectrometer(TOMS)Absorbing Aerosol Index(AAI).(2)The objective of this section is to understand the detailed characteristics and underlying mechanisms of dust aerosol at SACOL during dust plume.During dust plume,the mass concentration of PM₁₀can rise to～2484.72 ug/m³,～13 times as high as that in non-dust plume period.The meteorological analysis indicates that these polluted layers are not from local sources during dust plume and this large-scale transport of dust and pollutants remains a major uncertainty in quantifying the global effect of emissions from Northern China.Local air pollution can reflect the absorbing and scattering properties more effective than dust aerosol.(3)The objective of this section is to understand the detailed characteristics and underlying mechanisms of aerosol physical and optical parameters over China Loess Plateau and its potential impacts on the regional/global climate.To meet this goal,several ground instruments were performed from May 1 2007 to May 31,2008 at an integrated observational site of China (35.57N,104.08E).Results indicate that The type of aerosol is more complicated over China loess Plateau.The seasonal and diurnal variations of the larger accumulation mode and the coarse mode particle number concentrations(N_0.5-1and N_1-20,respectively)exhibited a seasonal cycle with the highest values in winter-spring and the lowest value in summer-autumn.a two-year data set of aerosol optical properties obtained from the AERONET is analyzed focusing on the western part of China.The aerosol optical depth standard product(AOD at 500 nm)is employed to evaluate the inter-annual and seasonal variability of the aerosol properties over SACOL.The AOD shoms that the high value during winter period and low value in winter period.This result shows that the air pollution in winter is heavy by the biomass burning(clearing of agricultural land).(4)Based on the available data from surface synoptic reports(8 times every day),the temporal and spatial distribution characteristics of sand/dust storms in China in the spring of 2002 are analyzed.The results show that there were mainly twelve dust storm weather processes including five severe dust storm events in China, among which the event on March 18—22 had the largest area and highest intensity.It has been found that most dust storm weather processes concentrated in early spring(from March to mid April)of 2002.The chemical composion of dust aerosol was analysed during spring,2002 in Lanzhou,Wuwei and Gaolan, which is the key region for major dust plume frequently influenced during its transportation from the dust original regions.Results shows that the mass concentration of trace elements include Hf,Ta,Ag,Cr,Hb increase quickly during dust plume.