Maha Harhash

Cairo Air Pollution and Climate (CAPAC) is dedicated to the understanding of the urban energy balance in Cairo, Egypt, through measurements from space and at ground stations. The in situ measurements will provide a focussed insight into three carefully chosen microclimates (urban, suburban-agriculture, and suburban-desert) and provide at the same time ground-truth data for satellite image analysis, which will expand the acquired knowledge into the spatial domain. In situ measurements were made during a field campaign in Greater Cairo from November 2007 to February 2008. In this study, the dataset of the CAPAC measurement campaign will be presented and analysed in terms of use for a remote sensing study. Measured variables complied with our expectations. The urban area featured a distinct nocturnal heat island. During the day the choice of reference station was responsible for the magnitude of the heat island. The diurnal cycle of radiative temperature at the suburban-desert station clearly exceeded the one at the urban station, thus the urban setting seemed to have a better heat storage than the suburban-desert. The stations also determined the partitioning of the turbulent heat fluxes. While in Cairo and at the suburban-desert station most of the available energy was partitioned into the sensible heat flux, the suburban-agricultural station maintained a high latent heat flux. The radiation and soil heat flux measurements proved to be applicable for comparison with remotely sensed data. However, the analysis of the turbulent heat fluxes showed that several constraints exist: measured fluxes tend to underestimate the actual flux and directional effects complicate the interpretation. An energy balance closure and footprint modelling is necessary to compare measured fluxes with satellite image retrieved products. Finally, turbulent fluxes are time averages, which is contrary to the remote sensing principle. Consequently, a direct use is problematic. Copyright © 2010 Royal Meteorological Society

Bulk aerosols sampled on a weekly basis at two Cairo (Egypt) urban sites from January 2003 to May 2006 were analysed for their chemical composition of major aerosol species (elemental carbon, water soluble/insoluble organic carbon, nitrate, sulphate, ammonium, chloride, sodium and calcium). Data subsequently obtained constitute one of the longest and more detailed dataset related to Cairo aerosols, and offer the opportunity to investigate seasonal trends. Dust aerosols (derived from calcium measurements) displayed maximum concentrations in spring and winter, due to frequent dust storms, but also high background concentration levels (∼50μgm−3) all year long. Within these particles, about 40% on average of Ca2+ was found to be associated with SO42−, NO3− and/or Cl−, pointing out “dust anthropization” processes and their subsequent climatic impact on a regional scale. Seasonal variations of non-dust aerosols, equally distributed between carbonaceous aerosols and ions, were also observed, with concentrations of the order of 100μgm−3 in autumn and winter, and of 60μgm−3 in spring and summer. High concentration levels of non-sea-salt chloride (up to 15μgm−3 on a monthly basis), likely of industrial origin, were observed in autumn and winter. During the autumn “Black Cloud” event, biomass burning aerosols originating from rice straw burning in the Nile Delta have shown to account for 12%, 35% and 50% of Cairo EC, WIOC and WSOC mass concentrations, respectively. Finally, relatively low WSOC/OC ratios (∼1/3) were obtained all the year long, calling for more investigation on the water-solubility of organic aerosols originating from the burning of agricultural waste, and on that of secondary organic aerosols formed in dry urban atmospheres.