ANGEO Annales Geophysicae ANGEO 1432-0576 Copernicus GmbH Göttingen, Germany 10.5194/angeo-27-2869-2009 Transport of dust and anthropogenic aerosols across Alexandria, Egypt El-Askary H. 1 2 3 4 Farouk R. 3 Ichoku C. 5 Kafatos M. 1 2 Department of Physics Computational Science, and Engineering, Schmid College of Science, Chapman University, Orange, CA 92866, USA Center of Excellence in Earth Observing, Chapman University, Orange, CA 92866, USA Department of Environmental Sciences, Faculty of Science, Alexandria University, Moharem Bek, Alexandria, 21522, Egypt National Authority for Remote Sensing and Space Science (NARSS), Cairo, Egypt Climate & Radiation Branch, Code 613.2, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA 21 07 2009 27 7 2869 2879 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.ann-geophys.net/27/2869/2009/angeo-27-2869-2009.html The full text article is available as a PDF file from http://www.ann-geophys.net/27/2869/2009/angeo-27-2869-2009.pdf

The flow of pollutants from Europe and desert dust to Europe from the Sahara desert both affects the air quality of the coastal regions of Egypt. As such, measurements from both ground and satellite observations assume great importance to ascertain the conditions and flow affecting the Nile Delta and the large city of Alexandria. We note that special weather conditions prevailing in the Mediterranean Sea result in a westerly wind flow pattern during spring and from North to South during the summer. Such flow patterns transport dust-loaded and polluted air masses from the Sahara desert and Europe, respectively, through Alexandria, and the Nile Delta in Egypt. We have carried out measurements acquired with a ground- based portable sun photometer (Microtops II) and the satellite-borne TERRA/Moderate Resolution Imaging Spectroradiometer (MODIS) sensor during the periods of October 1999–August 2001 and July 2002–September 2003. These measurements show a seasonal variability in aerosol optical depth (AOD) following these flow patterns. Maximum aerosol loadings accompanied by total precipitable water vapor (W) enhancements are observed during the spring and summer seasons. Pronounced changes have been observed in the Ångström exponent (α) derived from ground-based measurements over Alexandria (31.14° N, 29.59° E) during both dust and pollution periods. We have followed up the observations with a 3-day back-trajectories model to trace the probable sources and pathways of the air masses causing the observed aerosol loadings. We have also used other NASA model outputs to estimate the sea salt, dust, sulfates and black carbon AOD spatial distributions during different seasons. Our results reveal the probable source regions of these aerosol types, showing agreement with the trajectory and Ångström exponent analysis results. It is confirmed that Alexandria is subjected to different atmospheric conditions involving dust, pollution, mixed aerosols and clean sky.

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