Assessment of AOD variability over Saudi Arabia using MODIS Deep Blue products * Mohsin Jamil Butt * , Mazen Ebraheem Assiri, Md. Arfan Ali Department of Meteorology, Faculty of Meteorology, Environment and Arid Land Agriculture, King Abdulaziz University, Jeddah, Saudi Arabia article info Article history: Received 13 February 2017 Received in revised form 15 July 2017 Accepted 31 July 2017 Keywords: Aerosol AOD MODIS AERONET DB abstract The aim of this study is to investigate the variability of aerosol over The Kingdom of Saudi Arabia. For this analysis, Moderate Resolution Imaging Spectroradiometer (MODIS) Deep Blue (DB) Aerosol Optical Depth (AOD) product from Terra and Aqua satellites for the years 2000e2013 is used. The product is validated using AERONET data from ground stations, which are situated at Solar Village Riyadh and King Abdullah University of Science and Technology (KAUST) Jeddah. The results show that both Terra and Aqua sat- ellites exhibit a tendency to show the spatial variation of AOD with Aqua being better than Terra to represent the ground based AOD measurements over the study region. The results also show that the eastern, central, and southern regions of the country have a high concentration of AOD during the study period. The validation results show the highest correlation coefficient between Aqua and KAUST data with a value of 0.79, whilst the Aqua and Solar Village based AOD indicates the lowest Root Mean Square Error (RMSE) and Mean Absolute Error (MAE) values which are, 0.17 and 0.12 respectively. Furthermore, the Relative Mean Bias (RMB) based analysis show that the DB algorithm overestimates the AOD when using Terra and Solar Village data, while it underestimates the AOD when using Aqua with Solar Village and KAUST data. The RMB value for Aqua and Solar Village data indicates that the DB algorithm is close to normal in the study region. © 2017 Elsevier Ltd. All rights reserved. 1. Introduction Aerosols are the mixture of solid and liquid particles (such as dust, mist, fog, industrial emission, anthropogenic emissions, and organic particles) that can significantly alter the earth-atmospheric energy balance (Gupta et al., 2013; Papadimas et al., 2008). Aerosols can significantly influence hydrological cycles, ecosystem, and precipitation, and consequently, they can have major impacts on human health and agriculture (Hu et al., 2014). IPCC (2007) has documented aerosols as the prime aspect in the global climate change. Thus, the contribution of the natural, as well as anthro- pogenic emissions to the aerosol budget is one of the key element in the Earth's global climate system. It is therefore essential to monitor the daily aerosol variability to obtain the global aerosol budget in order to estimate the aerosol radiative forcing of climate. The aerosols' variability with respect to time is associated with various processes in a particular region. For example, over South America, high amounts of aerosols arise from July to September. Over the region of Central America, the same is true from March to May, over Central and southern Africa, the condition holds true from June to September, and over Southeast Asia, the high amounts of aerosols arise from the months of January to April (Xian, 2016). However, in The Kingdom of Saudi Arabia (KSA), the variability in aerosol concentration is highly associated with frequency of sand and dust storm events from May to August (Xian, 2016). It is documented that KSA is one of the major sources of aerosol (including natural and anthropogenic components) deposition in the world (Rushdi et al., 2010, 2013). In KSA, researchers have documented an increasing trend in the dust storm events, consti- tuting an increase in the atmospheric aerosol concentration (Nafiseh et al., 2014; Sultan et al., 2013), which subsequently not only disrupts everyday life, but also has an immense impact on human health (Yan et al., 2013). It is therefore very important to monitor and analyze the aerosols’ concentration in a region like KSA where dust and sand storms are common phenomena. How- ever, due to severe gaps in terms of the coverage by surface observational stations, a keen interest has been developed in the applications of satellite data for aerosol monitoring in KSA * This paper has been recommended for acceptance by Baoshan Xing. * Corresponding author. E-mail address: mbutt@kau.edu.sa (M.J. Butt). Contents lists available at ScienceDirect Environmental Pollution journal homepage: www.elsevier.com/locate/envpol http://dx.doi.org/10.1016/j.envpol.2017.07.104 0269-7491/© 2017 Elsevier Ltd. All rights reserved. Environmental Pollution 231 (2017) 143e153