Aerosol optical propertieslike Aerosol Optical Depth (AOD), Angstrom Exponent (AE), ASYmmetry parameter(ASY), Single Scattering Albedo (SSA), and Aerosol Volume Size Distribution(AVSD) have been analyzed for the atmosphere of Zanjan, a city in NorthwestIran. These properties have been studied usingthe ground-based AErosol RObotic NETwork (AERONET)duringthe periods from 8 to18 May and 8 to 14 June, 2013. During thestudy period, 14th May and 10th June are identified asdusty days, and AOD at 500 nm reached a peak value of 0.64 and 0.80, on thesedays. The high values of AOD and low values of AE during dusty days illustratethat coarse mode particles like dust are dominant. In the visible spectrum ASY usually decreasesand then somewhat increases in the near infrared region. Both SSA and AVSD suggest predominance of coarseparticles on the dusty days. The Santa Barbara DISORT AtmosphericRadiative Transfer (SBDART) model is utilized to simulate the solar irradiancevalues for the above-mentioned periods at the earth's surface, within theatmosphere, and at the Top of the Atmosphere (TOA). The results show thatdominant aerosol types are dust particles which have a coolingeffect on the earth's surfaceduring the studyperiods, especially on two dusty days, 14 May, and10 June. The correlation coefficient shows a very good agreement between theARF values retrieved from AERONET and SBDART simulation results.