Aerosol optical properties and radiative forcing over Zanjan

Aerosols can change the amount of radiative fluxes at the top of the atmosphere and at the surface. In this study aerosol optical properties like aerosol optical depth (AOD), angstrom exponent (alpha), asymmetry parameter (ASY) and single scattering albedo (SSA) were analyzed through the ground-based Aerosol Robotic Network (AERONET) over Zanjan for the period of 2011. The strong spectral dependence of AOD was demonstrated, i.e. AOD values of longer wavelengths are lower than shorter wavelengths. From March AOD starts increasing. The AOD values for May 2011 are the highest at all wavelengths. The results show that the value of AOD at 500 nm varies from 0.02 to 3.14, with an average of 0.24. The relationship between AOD and alpha shows an inverse relationship between them. The ASY decreases with wavelength and is strongly wavelength dependent, unlike SSA that shows a negligible dependence on wavelength. The radiative transfer model (SBDART) was utilized to simulate the solar irradiance values at the earthʹs surface and the top of the atmosphere using aerosol properties retrieved from Zanjan CIMEL sunphotometer measurements as input. Large differences between ARF on top of the atmosphere and the surface, demonstrates that aerosols have a cooling effect on the atmosphere. Hence, dust particles are the best candidate for aerosols of the area.