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Aerosol properties and their spatial and temporal variations over North China were analysed based on ground-based radiometer data for spring 2001. On the basis of the retrievals from sun/sky radiance and broad-band radiation measurements at four AERONET stations and eight first-class radiation stations over North China, the analysis comprised a detailed description of aerosol loading, size and absorption in this period. The impact of dust events on aerosol properties over the downwind region was emphasized.Heavy aerosol loading and notable temporal variation over North China were revealed by both datasets. The average aerosol optical depth at 750 nm at the eight radiation stations ranged from 0.32 in Ejinaqi to 0.68 in Beijing, with the averaged coefficient of variation being 70%. Aerosol optical depth was dominantly contributed to by dust over western China, with 68% (±5%) of aerosol optical depth at 550 nm being attributed to large dust aerosols. A dramatic increase in aerosol optical depth associated with the remarkable decrease in theÅngstrom wavelength exponent was observed in Beijing and Xianghe during the dust episode. This indicated that a huge number of large particles were emitted into the atmosphere during the dust period, with the result that the contribution to aerosol optical depth from coarse particles approached the value observed in the dust source region.Anthropogenic pollution also frequently contributed to the high aerosol optical depth in Beijing and Xianghe, but this was characterized by fine particles, with more than 70% of aerosol optical depth at 550 nm being attributed to fine particles. Pure desert aerosol in Chinese dust source regions absorbs much less solar radiation than predicted by known aerosol models. The retrieved single-scattering albedo was around 0.98 (±0.01) and had little wavelength dependence, which is in agreement with the ground-based and satellite retrievals in other dust source regions. Contrarily, anthropogenic aerosol exhibits much stronger absorption in the urban region, with the single-scattering albedo ranging from 0.89± 0.04 (at 440 nm) to 0.83± 0.05 (at 1020 nm). Due to the large difference in the absorption between dust and anthropogenic aerosol, the consequence of the input of a large volume of dust aerosols is not only to enhance the aerosol loading but also to reduce the aerosol absorption. Retrievals in Beijing showed that the single-scattering albedo increased to about 0.90 and had little spectral dependence when anthropogenic pollution and a dust event together affected Beijing; as for the pure dust period, it ranged from 0.92 at 440 nm to 0.97 at 1020 nm. The significant decrease in the aerosol absorption due to the dust outbreak can result in a decrease in aerosol atmospheric heating efficiency; this warrants further research since the increasing trend of aerosol loading with strong absorption in China is supposed to play an active role in regional and global climate change and the hydrological cycle. [ABSTRACT FROM AUTHOR]

MODIS aerosol retrievals onboard Terra/Aqua and ground truth data obtained from AERONET ( Aerosol Robtic Network) solar direct radiance measurements are collocated to evaluate the quality of the former in East Asia. AERONET stations in East Asia are separated into two groups according to their locations and the preliminary validation results for each station. The validation results showed that the accuracy of MODIS aerosol retrievals in East Asia is a little worse than that obtained in other regions such as Eastern U.S. . Western Europe. Brazil and so on. The primary reason Es due to the improper aerosol model used in MODIS aerosol retrievals algorithm so it is of significance to characterize aerosol properties properly according to long term ground-based remote sensing or other relevant in situ observations in order to improve MODIS retrievals in East Asia. Cloud contamination is proved to be one of large errors, which is demonstrated by the significant relation between MODIS aerosol retrievals versus cloud as well as notable improvement of linear relation between satellite and ground aerosol data after potential cloud contamination screened. Hence, it is suggested that more stringent clear sky condition be set in use of MODIS aerosol data. It should be pointed out that the improvement might be offset by other error sources in some cases because of complex relation between different errors. Large seasonal variation of surface reflection and uncertainties associated with it result in large intercepts and random error in MODIS aerosol retrievals in northern inland of East Asia. It remains to be a big problem to retrieve aerosols accurately in inland characterized by relatively larger surface reflection than the requirement in MODIS aerosol retrieval algorithm. [ABSTRACT FROM AUTHOR]

To understand the atmospheric background in North China and evaluate the effect of pollutant emission control as well as the influence of contaminant transportation in the regional pollution, during the 2008 Olympic Games, concentrations of four main air pollutants were observed from June to November at Xinglong station which is the regional background station of North China. We compared the concentrations and diurnal variations in different periods, analyzed the pollution transportation using the ground meteorological data and the backward trajectory model and compared the concentrations between different observation stations in Northern China. The results indicated that the concentrations of NOx, SO2, O3 and PM2.5 in summer were 8.4, 10.5, 126.0 and 59.8 microg x m(-3) respectively and in autumn were 11.7, 17.2, 97.5 and 30.7 microg x m(-3) respectively. During the period of Olympic (2008-08-08-2008-08-24), the concentrations of NOx, SO2, O3 and PM2.5 were 6.6, 6.8, 100.5 and 33.3 microg x m(-3) and reduced 29.0%, 46.9%, 18.6% and 36.5% respectively compared to the average concentrations of the period before and after Olympic Games. The concentration of NOx has reduced 62.5% and the PM2.5 has reduced 29.0% compared to the same term of Olympic in 2007. The air quality has obvious improvement in North China during the Olympic Games. Before the emission control, the concentrations of pollutants were lower in the night and became higher gradually in the daytime and reached the peak values in 17:00-20:00 which can indicate the accumulation of regional pollution transportation in Xinlong. In the emission control period, the accumulation of pollutants in afternoon was obviously weakened and the transportation of pollutants was lower which can reveal the obvious effect of the emission control in Beijing and peripheral areas. The atmosphere in Xinglong was mainly influenced by the monsoon from south direction in summer and autumn and the pollution of Xinglong was seriously influenced by the regional pollution in the south direction. Compared the concentrations between different stations, we can conclude that in summer and autumn the pollutions of NOx and SO2 are relatively lower, the pollution of O3 is not allowed to be optimism and the pollution of PM2.5 is very serious which should be paid enough attentions to.

Based on the atmospheric ozone sounding data, the average monthly and seasonal variety principles of atmospheric ozone concentration during six years are analyzed under the boundary layer in Beijing. The results show that the monthly variation of atmospheric ozone are obvious that the minimum values appear in January from less than 10 x 10(-9) on ground to less than 50 x 10(-9) on upper layer (2 km), but the maximum values appear in June from 85 x 10(-9) on ground to more than 90 x 10(-9) on upper layer. The seasonal variation is also clear that the least atmospheric ozone concentration is in winter and the most is in summer, but variety from ground to upper layer is largest in winter and least in summer. According to the type of outline, the outline of ozone concentration is composite of three types which are winter type, summer type and spring-autumn type. The monthly ozone concentration in different heights is quite different. After analyzing the relationship between ozone concentration and meteorological factors, such as temperature and humidity, we find ozone concentration on ground is linear with temperature and the correlation coefficient is more than 85 percent.

Much of the current uncertainty in the quantitative assessment of the climate and environment change is due to our lack of knowledge of the aerosol, for which the large-scale sun hazemeter ground-based network directly provides basic data. The data also can revise the results of the satellite remote sensing. Depending on the stations of CERN, the standard network was first built in China. The accurate and reliable hazemeter (LEDs) was uniformly used in the network. The hazemeters were calibrated by Langley plot method and transfer calibration and were uniformly checked. The AODs, which were synchronously retrieved from hazemeters (RSD < 3%) and CEMIL (RSD < 5%), were coherent and comparable. The stability and reliability of the hazemeters and the network was approved.

Atmospheric aerosol optical depth (AOD(lamda=500 nm)), Angstrom turbidity coefficient (beta) and Angstrom wavelength exponent (alpha) are obtained using the CERN sun hazemeter network from Aug to Dec, 2004. The results are as follows: At the Tibetan Plateau, Haibei and Lhasa, the mean of AOD is 0.09, 0.12; the mean of beta is 0.05, 0.13; the mean of a is 1.09, 0.06, respectively. At the Northeast of China, Hailun and Sanjiang, the mean of AOD is 0.14, 0.15; the mean of beta is 0.04, 0.06; the mean of a is 2.32, 1.58, respectively. At the desert region of North China, e.g., Fukang, Shapotou and Eerduosi, the range of averaged AOD is from 0.17 to 0.32; the range of averaged beta is from 0.09 to 0.19; the range of averaged a is from 0.68.to 1.28. At the forest areas, e.g. Changbai Mountain, Beijing forest and Xishuangbanna, the range of averaged AOD is from 0.19 to 0.42; the range of averaged beta is from 0.12 to 0.19; the range of averaged a is from 1.11 to 1.25. At agriculture areas, e.g. Shenyang, Fengqiu, Taoyuan and Yanting, the range of averaged AOD is from 0.34 to 0.68; the range of averaged beta is from 0.18 to 0.38; the range of averaged a is from 0.97 to 1.39. At the littoral areas and the lake of East China, e.g. Jiaozhou Bay, Shanghai City and Tai Lake, the range of averaged AOD is from 0.49 to 0.68; the range of averaged beta is from 0.21 to 0.29; the range of averaged a is from 1.24 to 1.37. At the inland cities, Beijing City and Lanzhou City, the mean of AOD is 0.47, 0.81; the mean of beta is 0.20, 0.45; the mean of a is 1.66, 0.89, respectively. The variations of aerosol properties at nineteen stations are explained in the paper.