The Cairo Aerosol Characterization Experiment (CACHE) was designed and carried out during two intensive observation periods (30 October–15 November 2004, and 20 March–14 April 2005) based on the terraced roof (20 m above ground level, agl) of the Physics Department of Cairo University (Giza, 30°01?34.3N; 31°12?26.4E). It is located in the southern part of Greater Cairo, about 3 km in a bee-line from the city centre (Sadate Square). The university is surrounded by open spaces, including the zoological garden, and the sampling site is at a distance of more than 200vm from the closest street.