Evaluating the effect of the atmospheric pollutants on the received solar radiation by ground surface using Angstrom-Prescott model (Case study: Urmia and Tabriz)

Solar radiation is one of the most important climate parameters that has direct relationship with many hydrological and meteorological processes. Due to the lack of real time records of this parameter in meteorological stations, solar radiation estimation models based on meteorological parameters are usually applied in practical issues. The Angstrom-Prescott equation that works on the basis of the sunshine hours has been widely applied for calculating solar radiation values due to its simplicity and acceptability. So far, many studies have been conducted about calibrating coefficients of this equation based on the meteorological parameters. The purpose of this study was to evaluate the atmospheric air polutions effects on received solar radiation using the Angstrom-Prescott model. Calibration of the Angstrom-Prescott equation coefficients was performed using daily radiation data of Urmia and Tabriz stations during 3 years period (2014-2017) with taking into account the Air Pollution Index (API). Also,in order to compare the results of modified models with general equation of Angstrom-Prescott,different linear,exponential and logarithmic models were developed. In order to evaluate the models precision, RMSE, MABE, NSE and R2 indices were employed. The results of statistical analysis of the models indicated that the calibrated models of Urmia and Tabriz stations on the basis of the API and the logarithmic structure had the best perfermace to general equation of Angstrom-Prescott. The average values of the RMSE of the modified logarithmic model for Urmia and Tabriz were obtained 0.1263 and 0.1050 jcm-2day-1, respectively.