Aerosol Optical Properties And Modeling Study In The East China Seas

As the East China Seas are close to the Asian continent, they are significantlyinfluenced by the Asian continent. Soot from urban industrial pollution, fossil fuelcombustion and biomass burning, as well as desert dust from the arid regions ofnorthwest China, are important sources of aerosols over the East China Seas.Atmospheric aerosols in this region mostly show strong absorption, which is quitedifferent from the non-absorbing aerosols over open ocean. The aerosols researchover the East China Seas can help us develop a more suitable set of aerosol models forthis region, and improve the accuracy of atmospheric correction in the East ChinaSeas.Based on the in-situ data of five cruises, aerosol optical properties over the EastChina Seas are analyzed. And the set of aerosol models in SeaDAS is evaluated toverify its applicability in the East China Seas. Results show that dust aerosols andsoot aerosols play an important role in this region. Most of aerosols in this regionshow weak absorption but there is still a certain percentage of strong scattering andstrong absorbing aerosols. This indicates that the influence of absorbing aerosols suchas dust and soot cannot be ignored. The real part of aerosol complex refractive indexis mainly between1.35and1.62, and the imaginary part of complex refractive indexvaries with wavelength. Aerosol volume size distributions in this region mainly havetwo peaks (respectively represent the coarse mode and fine mode), but there is anotherinconspicuous peak between the two peaks. So it’s better to describe the aerosolvolume size distribution in this region by a sum of three lognormal distributions thanby two. Scattering phase function is closely related to size distribution and aerosolabsorption. The result of aerosol model evaluation shows that when dealing withabsorbing aerosol, the SeaDAS6.2aerosol model usually results in underestimate ofaerosol optical thickness in blue-violet band and miscalculation of normalizedwater-leaving radiances. And the comparison between the in-situ data and SeaDAS aerosol model shows that the single scattering albedo and phase function are notexactly the same as the actual situation in the East China Seas. So in the East ChinaSeas the absorbing aerosol should not be ignored. While the current SeaDAS aerosolmodels are mainly designed for non-absorbing or weak-absorbing aerosols, andcannot entirely meet the requirements of atmospheric correction in the East ChinaSeas.Furthermore, referred to the SeaDAS6.2aerosol models, a new set of aerosolmodels for the East China Seas was derived from the AERONET observations. Dustand soot are added to the new model as they have significant influence in this region.Then the new models are evaluated by radiative transfer simulation. Preliminaryresults show that the single scattering albedo of the new aerosol models are closer tothe actual situation and aerosol optical thickness gets a better agreement with thein-situ data than using SeaDAS6.2aerosol models. While the angstrom exponent getsa slightly worse agreement.