GAW Report No. 205 - IGAC Project

CHAPTER 2 - AFRICAcycle with levels reaching 140 µg.m -3 in summer 2001 (Egyptian Environmental Affairs Agency,Environmental Information monitoring programme; http://www.eeaa.gov.eg/ eimp/news8.html).Khoder [2009] reported a year (Dec 2004-Nov 2005) of observations of ground level O 3 , nitrogendioxide (NO 2 ) and nitric oxide (NO) concentrations at Giza in the GCA. The mean values of O 3were about 44, 65, 91 and 58 ppb in daytime during the winter, spring, summer and autumnseasons, respectively. The diurnal cycles of O 3 concentrations during the four seasons revealed auni-modal peak in the mid-day time, with highest O 3 levels in summer due to the localphotochemical production. The diurnal variations in NO and NO 2 concentrations during the winterand summer showed two daily peaks linked to traffic density. The highest levels of NO X were foundin winter. Year-around, the observed mean daytime O 3 concentrations exceeded by about 35%(winter) to 100% (summer) of the days the Egyptian and European Union air quality standards of60 ppb for daytime (8-h) O 3 concentrations.Vrekoussis et al. [2009], based on SCIAMACHY satellite-sensor observations gridded into0.125x0.125 o girds over the GCA, deduced mean tropospheric NO 2 columns over the period 2003-2007 higher than 6 x 10 15 molecules cm -2 . They also derived an increasing trend that correspondsto 0.2-1.0 ppbv y -1 for this 4 years period.Abu-Allaban et al. [2009] also reported very high NMHC, including BTEX, in the GCAvarying from 365 ± 102 to 1849 ±298 ppb C in later winter and 462±315 to 2037±1369 ppb C inlate fall 1999. In summer 2004, observations of NMHC by Khoder [2007] at three locations, twourban areas in GCA and background one in the rural area in Menofiya province point to road trafficas the major source of aromatic NMHC. The mean concentrations of n-hexane, n-heptane,benzene, toluene, ethylbenzene, (m, p)-xylene, o-xylene, 1,3,5-trimethylbenzene and 1,2,4-trimethylbenzene were about 124, 71, 87, 214, 43, 141, 74, 31 and 65 µg m -3 , respectively in citycentre of Cairo where the total average concentration of NMHC was about 2 times higher thanthose found in other urban sites, and 22 times than those found in background sites. These levelswere among the highest reported for megacity regions [Khoder, 2007].Particulate matterAbu-Allaban et al. [2002; 2007] reported pollutant observations at 6 sites in the greaterCairo area from 1999 to 2002, showing average PM 10 (PM 2.5 ) mass ranged from 265 µg m -3 (216µg m -3 ) at an industrial site to 88 µg m -3 (30 µg m -3 ) at a residential location. High levels of tracemetals were also observed, with an average PM2.5 Pb level of 26.8 µg m -3 . Based on weeklyobservations from Jan 2003 to May 2006, Favez et al. [2008a] reported bulk aerosol seasonalmean levels of 115, 165, 215 and 190 µg m -3 during summer, autumn, winter and springrespectively at two urban sites in Cairo.Khoder [2002] measured sulphate (SO 4 = ) and nitrate (NO 3 - ) aerosol components and theirprecursor gases SO 2 , NΟ 2 , nitric acid (HNΟ 3 ) and O 3 during winter 1999-2000 and summer 2000.The average concentrations were 6.2 and 9.8 µg.m -3 for particulate nitrate, 1.1 and 6.7 µg.m -3 forgaseous nitric acid and 15.3 µg.m -3 and 25.1 µg.m -3 for particulate sulphate, during the winter andthe summer seasons, respectively. The highest average concentration ratio of gaseous nitric acidto total nitrate was found during the summer season. Particulate sulphate and nitrate and gaseousnitric acid concentrations were relatively higher in the daytime than in the nighttime.Favez et al. [2008a,b] reported more than 2 years of weekly observations of bulk aerosolsand their chemical characterization with respect to selected ionic species and carbonaceousaerosols (sum of elemental carbon (EC) and organic carbon (OC)) at two Cairo urban sites. Dustaerosols have been derived from calcium (Ca 2+ ) measurements and displayed high backgroundconcentration levels (50 µg m -3 ) all year long and maximum concentrations during the dust stormperiods [Favez et al., 2008a]. About 40% of Ca 2+ on these dust aerosols was found to beassociated with ions of anthropogenic origin like SO = 4 , NO - 3 and/or Cl - , pointing out human drivenprocesses that alter the chemical characteristics of dust and thus its climatic impact on a regionalscale. High concentration levels of non-sea-salt chloride (up to 15 µg m -3 on a monthly basis), likelyof industrial origin, were observed in autumn and winter.52