Seasonal Behaviours and Weekdays/Weekends Differences in Elemental Composition of Atmospheric Aerosols in Cairo, Egypt

The aim of the present study was to investigate the seasonal distributions and weekdays/weekends differences in ambient aerosols and their elemental contents in the atmosphere of the 15 May City, Egypt. Aerosol samples were collected from March 2009 to February 2010. The concentrations of 14 elements including Na, Mg, Ca, K, Al, Fe, Mn, Co, Cu, Zn, Ni, Cd, Pb and Cr were measured by Atomic Absorption Spectrophotometry (AAS). The mean aerosols concentrations were 290 µg/m3 (spring), 250 µg/m3 (summer), 330 µg/m3 (autumn) and 400 µg/m3 (winter). The measured elements showed a strong seasonal variation; with the highest concentrations in winter and the lowest in summer. Na, Mg, Ca, K, Al and Fe were the dominant elements, followed by Mn, Cu, Zn, Ni and Pb. The minimum concentrations were noted for Co, Cd and Cr. The dominant elements in aerosol represented 94%, 94.51%, 94.61% and 94.28% from the total measured elements and 5.08%, 5.74%, 6.11% and 5.44% from aerosol mass during winter, spring, summer and autumn, respectively. The aerosols concentrations on weekends were reduced by 31.25% in the winter and 15.2% in the summer. The concentrations of the measured elements were higher on weekdays than weekends. The weekday/weekend concentration ratios were 1.69 and 1.38 for total measured elements during winter and summer, respectively. The mean Ni and Cd levels were higher than the proposed WHO, USEPA and the European Community standards. Significant positive correlations were found between the concentrations of aerosols, Mg, Ca, K, Al, Fe, Mn, Co, Zn and Cr. The enrichment factors (EFs) and the non-crustal fractions of all elements indicated that Na, Mg, Ca, K, Fe and Mn originate mainly from soil sources, whereas Co, Cu, Zn, Ni, Cd, Pb and Cr are mostly emitted in the atmosphere of 15 May City from anthropogenic sources.