Investigation of aerosol optical thickness between 370 and 710 nm in the solar spectrum

Aerosol optical thickness is the most comprehensive variable to characterize aerosol, assess atmospheric pollution and make atmospheric corrections to satellite remotely sensed data from ground-based instruments. Scientists have much to learn about the way aerosols affect regional and global climate. Climate change studies in Mongolia clearly demonstrate that Mongolians should be concerned about climate change resulting from anthropogenic greenhouse gas (GHG) emissions. These studies suggest that during the last 60 years the average temperature in Mongolia has increased by about 1.56 degC. Photosynthetic active radiation (PAR) contributes significantly in comprehensive studies of radiation climate, remote sensing of vegetation, radiation regimes of plant canopy and photosynthesis. The PAR has been observed in Mongolian grassland for a long time. It is useful for not only vegetation but also atmospheric research, especially for aerosols, because of its major part of solar radiation. In this study, a method to estimate optical thickness of aerosol (AOT) has been developed with an error analysis and then the AOT has been derived from the PAR data in Mongolia during the period of 1985 to 2000. There are two remarkable features shown in the analytical results; the AOT in 1992 is temporarily increasing possibly due to the effect of Pinatubo eruption (June 1991), and after 1997 the AOT is gradually increasing and has a clear seasonal trend compared before 1995.