Variability of Aerosol Optical Depth during dust event over Karachi

This study investigated the changes in the parameters of aerosol during dusty and non-dusty days from 29th May to 06th June, 2014 over Karachi. We analyzed the effects of the dust storm event on the Aerosol Optical Depth (AOD) and Angstrom Exponent (AE) retrieved from ground-based Aerosol Robotic Network (AERONET) observations. We compared the daily averaged AOD550 and α470–670. During this study period the diurnal average AOD and AE values were in the range from 0.343 to 1.42 and 0.25 to 0.72 respectively. AOD values showed significant variability in this region during dust loading with the highest value of 1.42 on 31st May 2014. Whereas, on the same day AE value was low (0.25) indicating the dominance of dust particles. Variations in AOD during the dust storm were studied at five different wavelengths of 500, 675, 870, 1020 and 1640 nm, respectively. Dust storm of 31st May showed higher wavelength dependence as compared to non-dusty days. The Hybrid Single Lagrangian Integrated Trajectory (HYSPLIT) model was also utilized to find the tracks and origins for the dust transported to Karachi. The results showed that dust particles were coming from Yemen and Iran to Karachi.