Effect of dust loadings, meteorological conditions, and local emissions on aerosol mixing and loading variability over highly urbanized semiarid countries: United Arab Emirates case study

Long-term natural and anthropogenic aerosol characteristics over the United Arab Emirates (UAE) are investigated in this study. Aerosol characteristics were analyzed using data from the Moderate Resolution Imaging Spectroradiometer (MODIS), local meteorological stations, and the Aerosol Robotic Network (AERONET) ground-based station during 2006-2015. AOD values significantly increase during the spring and summer seasons and are associated with dust loading during major dust events. The mean annual variation of aerosol loading indicates about a 4.32 and a 11.36% change in the AOD and Angstrom Exponent (AE), respectively, during the study period. Monthly trends show larger AOD and AE variability, 5.4 and 37.8% respectively, with higher aerosol concentrations during the summer. In general, from November to March an upward trend in aerosol characteristics is observed from 2011 to 2015 compared to 2006-2010. In contrast, a neutral to weak decrease in AOD measurements are observed during April-September. Overall, this trend variability is sustained by natural aerosol emissions throughout the year. Meanwhile, a significant increase in AE was measured from May to August of 2011-2015 compared to 2006-2010. This is an indication of an increment of anthropogenic emissions from 2011 to 2015. A correlation between several meteorological parameters (temperature, relative humidity, wind speed, and wind direction) and MODIS measurements was performed to investigate the effect of local meteorological conditions on AOD from 2006 to 2015 over the UAE. Some statistical correlation was observed between AOD, wind speed, and air temperature. A weak correlation was observed between temperature, relative humidity, and AOD, while a strong correlation was observed between wind speed and AOD. Dry soil formed due to a lack of rainfall, along with high summer temperatures and high-speed winds which stimulate dust aerosol loading and lifetime in the atmosphere. Aerosol characteristics, including dominant aerosols, were identified over the UAE using the Mezaria AERONET station. Air mass flow towards the UAE from the North West (NW) and West (W) directions moves over highly polluted regions and desert areas. Coarse-mode aerosol particles dominate over the UAE during March-June associated with the dust season, while a high loading of fine-mode particles is mostly observed during September-January.