Beijing, China. – Human activities release aerosol particles into the atmosphere in many regions of the world, but particularly over East Asia where rapid human population and economic growth has resulted in increased energy consumption and an associated rise in air pollution. Recently, in a collaborative effort by the Institute of Atmospheric Physics (Chinese Academy of Sciences), University of Tokyo, National Institute for Environmental Studies of Japan, and University of Oxford, a series of studies using an online aerosol-coupled non-hydrostatic icosahedral atmospheric model have revealed a detailed global and regional picture of aerosol optical properties.

Aerosol optical properties such as aerosol optical thickness (AOT), ？ngstr？m Exponent (AE), and single scattering albedo (SSA) are key to revealing information on the aerosol column burdens and chemical components in the atmosphere. These properties can be simulated by aerosol models over global or regional scales, but are difficult to measure directly. “It is encouraging that the correlations between the model and ground-based site measurements at the global scale are high for both AOT and AE [values of 0.753 and 0.735, respectively], indicating that the model is suitable for studying the temporal and spatial variations of key aerosol optical properties and aerosol-related climate impacts at the global scale,” says Dr. DAI Tie, an assistant researcher at the Institute of Atmospheric Physics (Chinese Academy of Sciences) and member of the project team.

By separating the modeled aerosol optical properties into all-sky and clear-sky properties based on satellite observations, the effects of cloud on the evaluation of the performance of the aerosol model have also been investigated. Dr. DAI continues: “The largest differences between clear-sky and all-sky AOTs are found over East Asia. The maximum absolute and relative differences [greater than ？0.3 and ？30%, respectively] are found over eastern China in January, where aerosols derive mostly from pollution sources. This may be because sulfate aerosol is mostly formed in clouds and hygroscopic growth is more effective in higher humidity regions near to clouds.

"We have also developed an aerosol assimilation system to reproduce aerosol events of short duration, often missed by standard models because of the lack of accurate emissions data. We have found that the assimilation system overcomes the drawbacks of uncertainties in model parameterizations and time-invariant sources of anthropogenic aerosols to achieve improvements in the simulated AOTs at all the 12 ground-based sites over East Asia when satellite observations are assimilated every 6 hours. ”

An aerosol-coupled global non-hydrostatic model with a stretched-grid system has also been developed to simulate aerosols in a region scale of 10 km grids. The regional simulation requires neither a nesting technique nor lateral boundary conditions, as opposed to general regional models. “It generally reproduces monthly mean distributions of the observed sulfate and SO₂ over East Asia as well as the diurnal and synoptic variations of the observed ones around the target region, Tokyo/Japan.” says Dr. Daisuke GOTO, also a co-author of the studies at the National Institute for Environmental Studies of Japan.

The figure shows modeled AOTs at all AERONET (Aerosol Robotic Network) sites in East Asia are improved with data assimilation, especially for aerosol events of short duration. (Dai et al., 2014, Environmental Pollution)  

The project is supported by funding from the National Natural Science Foundation of China (41130104, and 41475031), the Public Meteorology Special Foundation of MOST (GYHY201406023), the National Key Basic Research and Development Program (973 Program, 2011CB403401), JAXA/EarthCARE (13RSTK-007543), the MEXT/VL for Climate System Diagnostics, the MOE/Global Environment Research Fund A-1101, NIES/GOSAT, NIES/CGER, the S-12 of the MOE, and MEXT/RECCA/SALSA (10101026). Recent journal papers have been published in Atmospheric Environment (doi:10.1016/j.atmosenv.2013.10.018), Environmental Pollution (doi:10.1016/j.envpol.2014.06.021 ), Advances in Atmospheric Science (doi: 10.1007/s00376-014-4098-z) , and Geoscientific Model Development Discussion (doi:10.5194/gmdd-7-131-2014).

Contact: Dr. DAI Tie, daitie@mail.iap.ac.cn