Dust characteristics and radiative properties: Implication to climatic impacts

Abstract Dust optical and radiative properties were analyzed in the urban environment of Karachi using Aerosol Robotik Network (AERONET) data. During the dusty days significant variations were found in Aerosol Optical Depth (AOD), aerosol Volume Size Distribution (VSD), Single Scattering Albedo (SSA), Asymmetry Parameter (ASY), Refractive Index (RI), and Aerosol Radiative Forcing (ARF). The AOD values were in the range from 0.95 to 2.07 during dusty days. The VSD in coarse mode aerosols was high during dusty days and no significant variations was found in VSD fine mode. The SSA values in dusty days were in the range from 0.91 to 0.99, which showed the existence of dust over the urban environment. The ASY and RI values indicated the predominance of mineral dust particles. The shortwave (SW) and longwave (LW) aerosol radiative forcing (ARF) were in the range from -0.01 to +97 𝑊𝑚−2, +29.2 to +14.6 𝑊𝑚−2 at the top of atmosphere, and -220 to +27.1 𝑊𝑚−2, +20.7 to +11.6 𝑊𝑚−2 at the earthʹs surface, respectively. The LW radiation, therefore produced significant warming both at the earthʹs surface and top of the atmosphere. The Hybrid Single Lagrangian Integrated Trajectory (HYSPLIT) model was used to investigate the origin of air masses in order to find the paths and source regions for the dust transported to Karachi. The results revealed that air masses arrived in Karachi were from Iran, Afghanistan, Russia, and the Middle East.