Khan Alam - Department of Physics, University of Peshawar, KPK, Pakistan
Samina Bibi - Department of Physics, University of Peshawar, KPK, Pakistan
Humera Bibi - Department of Physics, University of Peshawar, KPK, Pakistan

The present study analyzes the optical and radiative properties of aerosol during major dust episodes between 2010 and 2014 over Karachi, the mega city of Pakistan. First, these dust episodes were identified through Moderate resolution Imaging Spectroradiometer (MODIS) observation and then National Oceanic and Atmospheric Administration (NOAA) Hybrid Single Particle Langrangian Integrated Trajectory (HYSPLIT) model were used to explore the source regions and the possible transport of air masses reaching to the studied site. The data of aerosol optical properties were retrieved from Aerosol Robotic Network (AERONET) during the dust episodes. The results revealed that the values of Aerosol Optical Depth (AOD) were high during dust episodes mostly in spring and summer months, obtaining the maximum of 2.29 in July 2014. Aerosol Volume Size Distributions (VSD) exhibited a noticeable coarse mode peak value at a radius of 2.24 μm during dust episodes with the values ranged from 0.4 to 1.3. The Single Scattering Albedo (SSA) values abruptly increased with increasing wavelength during all the dust episodes over Karachi. Finally, the Aerosol Radiative Forcing (ARF) was estimated using the santa Barbra DISORT Atmospheric Radiative Transfer (SBDART) model. Calculations showed a negative ARF at the Top of Atmosphere (TOA) and at the SURface (SUR), with positive values within the atmosphere (ATMOS) during dust episodes throughout Karachi.

Dust Episodes, AOD, VSD, SSA, ARF