Changes in aerosol optical properties due to dust storms in the Middle East and Southwest Asia

Super dust storms occurred over the Middle East and southwest Asia on March 2012. These storms reduced the air quality over the Gulf Region, Iraq, Iran, and Pakistan. Airports were shut down due to poor visibility, schools were closed, and hundreds of people were hospitalized with respiratory problems. In order to better understand the effects of such dust storms we have analyzed aerosol optical and radiative properties during this event using data from the Moderate Resolution Imaging Spectroradiometer and the Aerosol Robotic Network. Maximum aerosol optical depth (AOD) values occurred on the 18th of March in Kuwait, Bahrain, Qatar, and Saudi Arabia, where values of 4.9, 4.4, 4.3, and 4.9 were recorded, respectively. In Oman, the Arabian Sea, and Iran, maximum AOD values occurred on the 19th of March, reaching 4.5, 5, and 5, respectively. The dust storm then spread across Pakistan, passing through Multan, Faisalabad, and Lahore where maximum AOD values of 2.1, 2.6, and 2.7, respectively, were attained on the 20th of March. The maximum aerosol volume size distributions (VSDs) in Lahore occurred on dusty days and minimum VSDs on non-dusty days. The VSD, single scattering albedo, refractive index, and asymmetry parameter values on dusty days suggested that dust aerosols were predominant over anthropogenic aerosols in these urban environments. The shortwave aerosol radiative forcing (ARF) values (on both dusty and non-dusty days) ranged between -50 W m(-2) and -194 W m(-2) (average: -114 +/- 40 W m(-2)) at the earth's surface, and between -31 W m(-2) and -105 W m(-2) (average: -58 +/- 25 W m(-2)) at the top of the atmosphere (TOA). The longwave aerosol ARF values ranged between + 6 W m(-2) and + 20W m(-2) (average: + 12 +/- 4 W m(-2)) at the earth's surface, and between + 7 W m(-2) and + 30 W m(-2) (average: + 16 +/- 7 W m(-2)) at the TOA. Longwave radiations therefore produced significant warming, both at the TOA and at the earth's surface. (C) 2014 Elsevier Inc. All rights reserved.