Seasonal and spatial variation of atmospheric particulate matter in a developing megacity, the Greater Cairo, Egypt

 

A. S. ZAKEY
The Abdus Salam International Centre of Theoretical Physics (ICTP)–Strada Costiera,
11 –34014 Trieste, Italy,
Egyptian Meteorological Authority, Qobry EL–Kobba, Cairo, Egypt, P.O. Box 11784 and
Department of Chemistry, Atmospheric Science, Göteborg University, SE–412 96 Göteborg, Sweden
Corresponding author; A. S. Zakey; e–mail: azakey@ictp.it

M. M. ABDEL–WAHAB
Cairo University, Department of Meteorology, Faculty of Science, Cairo, Egypt

J. B. C. PETTERSSON, M. J. GATARI, M. HALLQUIST
Department of Chemistry, Atmospheric Science, Göteborg University, SE–412 96 Göteborg, Sweden

 

Received July 25, 2006; accepted October 2, 2007

 

RESUMEN

Como ejemplo de una mega ciudad en desarrollo se evaluó el área del Gran Cairo, Egipto (GC) en relación con las partículas (PM) y el plomo (Pb) atmosféricos. Las partículas se colectaron durante 2001–2002 en dos tamaños de fracción, PM_2.5 y PM₁₀ de 17 sitios representativos de diferentes características (industriales, urbanas, residenciales y ambiente no alterado). Las concentraciones de partículas fueron en general altas, con promedios anuales de 85 ± 12 ug m^–3 para PM_2.5 y de 170 ± 25 para PM₁₀. En una escala anual, los niveles elevados de PM se deben a varias fuentes que incluyen el tráfico, la incineración de desechos, partículas de polvo transportadas por el viento desde el desierto fuera del GC, y dentro del GC desde la colina Moqattam. En una escala estacional, las concentraciones de PM son más elevadas en el sector industrial durante la primavera, la estación polvosa, debido al efecto combinado de las tormentas de polvo y las emisiones antrópicas en el GC. Las concentraciones estacionales más bajas se registraron en el verano en los sitios no alterados. Hubo un incremento notable en los niveles de PM durante el periodo de octubre a diciembre debido a la incineración de desechos de las cosechas de arroz en el área del delta del Nilo (al norte del Cairo). La relación PM_2.5/PM₁₀ más alta (0.59) que se registró corresponde al sector urbano, mientras que la más baja (0.32) es del sector residencial. Las muestras de PM_2.5 y PM₁₀ también se analizaron para Pb con el fin de determinar la influencia de diferentes fuentes de emisión. Las concentraciones promedio mensuales de Pb en PM_2.5 (Pb_2.5) y PM₁₀ (Pb10) variaron entre 0.4 y 1.8 µg m^–3 en los sitios no industriales. Las concentraciones fueron significativamente mayores en las áreas industriales, en las que se observó un máximo de 16 µg m^–3. Las concentraciones elevadas de Pb y PM determinadas contribuyen a la contaminación ambiental local. El GC está sujeto a concentraciones elevadas de partículas durante todo el año. No hay un límite anual para las concentraciones de PM₁₀ en la ley ambiental egipcia, pero al compararlas con los promedios de 24 h, las PM₁₀ representan riesgos de largo plazo a la salud ya que tienen efectos ambientales locales y regionales. Los muestreos de alto volumen de PM₁₀ considerados como promedios diarios muestran que los límites de calidad del aire se excedieron 60.47, 79.07 y 62.96 % en los sitios Heliopolis (35), Maadi (6) y 6 de Octubre (13) durante el periodo de medición de 2001 y 100, 91.7 y 89.8 % en Shoubra El–Kheima (20), El–Qolay Sq (1) y Abbasiya (36) durante el periodo de 2002. La evaluación de los datos presentados en este trabajo servirá como base para futuras modelaciones regionales y globales y para la clasificación de las fuentes.

 

ABSTRACT

As an example of a developing megacity the Greater Cairo (GC) area in Egypt has been evaluated with respect to atmospheric particulate matter (PM) and lead (Pb). Particulate matter was collected during 2001–2002 in the two size fractions PM_{2 5} and PM₁₀ at 17 sites representing different activities (industrial, urban, residential and background condition). The PM concentrations were generally high, with yearly average PM_2.5 and PM₁₀ values of 85 ± 12 and 170 ± 25 µg/m^-3, respectively. On an annual scale, the high PM levels were due to many sources that included traffic, waste burning and wind blown dust particles emitted from the desert outside GC and the Moqattam hill inside GC. On a seasonal scale, the PM concentrations were highest in the industrial sector during spring, the dusty season, due to the combined effect of dust storm events and anthropogenic emissions over GC. The lowest seasonal concentrations were recorded in the summer season at the background sites. There was a marked increase in PM levels during the period October to December due to burning of waste from harvested rice in the agriculture area in the Nile Delta (north of Cairo). The highest PM_2.5/PM₁₀ ratio was recorded in the urban sector (0.59) while the lowest ratio was recorded in the residential sector (0.32). The PM_2.5 and PM₁₀ samples were also analyzed for Pb in order to address the influence of different emission sources. The monthly average concentrations of Pb in both PM_2.5 (Pb_2.5) and PM₁₀ (Pb₁₀) varied between 0.4 and 1.8 ± µg m^–3 at the non industrial sites. The concentrations were significantly higher in the industrial areas, where concentration up to a maximum of 16 ± g m^–3 could be observed. Both the high lead and PM concentrations measured are contributing to local environmental pollution. GC is subjected to high concentrations of particulates most of the year. There is no annual limit for PM₁₀ concentrations in the Egyptian law of environment, but comparing to the 24 hour average, PM₁₀ is representing health risks on the long–term that will give both regionally and globally environmental effects. High volume samplers measuring PM₁₀ as daily average shows that the air quality limit value has been exceeded at sites Heliopolis (35), Maadi (6) and 6th October (13) during 60.47, 79.07, and 62.96% of the measuring period of 2001, and at Shoubra El–Kheima (20), El–Qolaly Sq (1), and Abbasiya (36) during 100.0, 91.7, and 89.8% of the measuring period of 2002. Thus, the evaluation of the data presented in this paper will serve as a basis for future regional and global modelling and source apportionment.

Keywords: Megacity, lead, air quality, air pollution, dust storm, PM₁₀, PM_2.5.

 

1. Introduction

The megacities of the world are facing serious air quality problems (Molina and Molina, 2004). The Greater Cairo (GC) area in Egypt is the largest city in Africa and the Middle East with a population of over 15 million people, and it is one of the 15 largest cities in the world. Urbanization and industrialization have increased very rapidly, particularly in the second half of the last century, causing increased levels of air pollutants and environmental hazards (Robaa and Hafez, 2002; Robaa, 2003). The air pollutant levels are not only an environmental issue within the city itself, but also affect regional and global environment. The GC area serves as an example of a developing megacity. Transportation (more than 1.5 million vehicles), industries and waste burning are common major sources of gaseous and particulate air pollution in megacities (Molina and Molina, 2004). Particulate matter (PM) concentration is significantly enhanced by further contributions of wind blown dust from the surrounding arid areas.

The severe air pollution combined with meteorological conditions and seasonal variations motivated detailed characterization of the air quality situation in GC. Of particular interest in the present study are the PM and Pb concentrations in GC during 2001–2002 starting from January to December. Previous investigations have shown high levels of PM₁₀ (three times WHO standards 60 ± (µg m^–3). For example, a study by Rodes et al. (1996) measured PM concentrations in Cairo during the period from December 1994 to November 1995, and the annual average PM₁₀ concentrations were concluded to exceed 150 (µg m^–3 at most measurement sites.

Pb in particulate matter is known to cause severe health problems and the concentration levels reported in previous studies were high by any standards. For example Ali et al. (1986) measured an annual mean lead concentration of 4.2 µgm ^–3 at a site near traffic, with a highest monthly average value observed in July (5.4 µgm^–3) and lowest in January (3.7 µgm^–3). Hassanien et al. (2001) showed an improvement where they observed a decrease by 40 % in Pb concentration in the urban sector of GC from 1994 to 1997 as a result of Pb reduction from traffic (diesel buses and gasoline cars). Even if the conditions have improved, reported Pb concentrations in GC are still higher than those recorded in other parts of the world (Querol et al., 1999; Watson and Chow, 2001; El–Tahir et al., 2004). The environmental effects of Pb in GC have been demonstrated by measurements of Pb levels in the blood of Cairo traffic policemen (Kamal et al., 1991), and in studies on crops grown near highways (Belal and Saleh, 1978; Noweir, 1990).

There are great needs for better characterization of seasonal and long–term variations in PM and Pb concentrations in GC, as well as a better understanding of the governing effects of meteorology and changes in urban development. This paper presents mass concentrations of PM_2.5, PM₁₀ and their Pb content obtained from measurements at 17 sites in GC over the period 2001–2002. These sites are classified into different areas according to local activities, i.e. industrial, urban, residential and background. The seasonal variations in concentrations are presented, and discussed in relation to natural and anthropogenic activities taking place during different parts of the year.

 

2. Experimental

2.1 Site description and climate

Greater Cairo is situated south of the delta in the Nile basin. The population exceeds 15 millions concentrated over an area of about 200 km², i.e. an area 4 km wide and stretching 50 km along the banks of the Nile river. Climatologically, GC is in the subtropical region. The city is characterized by the presence of the Moqattam hill (inside GC) to the east and southeast, and desert areas (outside GC) extending in the west and east directions. Among the outstanding weather events are dust and sand storms that frequently occur in spring (March to May) and autumn (September to November) (Zakey and Omran, 1997). In spring, hot desert cyclones known as the "Khamasin" depressions pass over the desert. These cyclones are always associated with strong hot and dry winds that are often laden with dust and sand that increase PM levels. In winter (December to February) the general climate is cold, humid and rainy; while during the summer season (June to August) the predominant weather is hot and dry

Figure 1 shows the map of GC including the measurements sites. The measurement took place at 31 sites within GC of which 17 sites have PM₁₀ and PM_2.5 measurements and the other sites have gaseous measurements only (NO₂, SO₂, O₃). The selected sites for PM measurements represent different activities and are spatially distributed over GC. Summary and activity classifications of the selected sites are shown in Table I. The sites of Shoubra El–Kheima (20), Giza (30), Abbasiya (36), and Kaha (26) were chosen to represent the industrial, urban, residential and background, respectively.

2. 2 Sampling and analysis

Twenty four month (January to December) of PM samples were collected during the period 2001–2002. Air Metrics^TM samplers were used at each site to collect atmospheric PM for gravimetric and Pb analysis. In some of our sites we measure the PM using another techniques so–called beta gauge method, these sites are El–Qalay (1), Tebbin south (7) and Abbassaeya (36). The samplers were fitted with PM₁₀ and PM_2.5 heads, which are designed to select particles of aerodynamic diameter less than 10 µm and 2.5 µm respectively. Both PM_2.5 and PM₁₀ were sampled at all sites on 47 mm quartz fibre filters. The samplers were programmed to continuously collect a PM sample over a 24 h period ("0000" to "2400" (h)) and samples were retrieved from the sites on a scheduled program of every sixth day. At a few sites PM₁₀ was measured during selected episodes with high time resolution (hourly) using Β–attenuation detectors.

The PM mass deposited on the filters was determined by weighing the filters before and after sample collection using a microbalance. Prior to both the initial and final weighing, the filters were conditioned in a desiccation cabinet for at least 24 hours to stabilize the weight. The filter conditioning and weighing operations were performed in a room in which the air temperature and relative humidity were controlled within the ranges 17–23 °C and 45–55%, respectively.

After the final weighing, Pb was extracted from the PM by digesting the filters in hot nitric acid solution. Flame atomic absorption spectroscopy (FAAS) was used to determine the Pb concentration using the Pb absorption line at 217 µm. The analytical detection limit of this method corresponds to an atmospheric concentration of 0.17 µgm^–3 of particulate Pb in a 24 h sample. Before beginning analysis of samples, the FAAS response is calibrated using a reagent blank solution and standard lead solutions at five different concentration levels. A series of continuing calibration checks is performed during the analysis of each set of samples to verify that the FAAS calibration conditions do not shift beyond acceptable limits. The calibration of the FAAS is considered acceptable if the response for the blank sample is within ± 0.10 µm of Pb and the response for the 2.48 µg of Pb standard is in the range of 2.25–2.75, i.e. the deviation from the standard values is < 10%.

The data recovery/completeness values reported are expressed as a percentage of the total number of measurements that yielded a valid result. The annual average recoveries for PM and lead data are within an acceptable range (sampling events > 60%). However, data recoveries for a few sampling events were below acceptable levels. In particular, low PM_2.5 and PM₁₀ data recoveries of 35.7% and 36.8%, respectively, were obtained from the 27 August 2001 sampling event. In this case, data loss appears to result from a systematic error in the sample weights, possibly due to improper conditioning of the samples prior to gravimetric analysis (see Table II).

 

3. Results and discussion

3.1 Mass concentrations of PM10 and PM2.5

In 1994, the government of Egypt promulgated a law for the environment (EGL/94). The provisions of this law become effective in March 1998. EGL/94 specifies maximum limits for pollutants in ambient air (outdoors), workplace atmosphere, and source emissions. The limits established by EGL/94 for PM₁₀ and lead are shown in Table III.

Figure 2 shows the average mass concentrations of PM₁₀ and PM₂.₅ measured at each of the 17 sites during the measurement period. Each average and corresponding standard deviation represents approximately 120 samples. The daily PM₁₀ concentrations were in the range 82–253 (µg m^–3 as shown in Table IV. These values are all higher than the 24 h limit of 70 (µg m^–3 set by EGL/94 as shown in Table III and as such the limit is exceeded in all samples from all the sites. Among the sites, Tebbin south (7) recorded the highest mass concentration due to the cement and iron industrial activities in this area. The PM_2.5 concentrations in the samples were also high in all areas and ranged from 55 to 131 µgm^–3.

Figure 3 shows the PM_2.5/PM₁₀ mass ratio from the 24 hours samples at all sites. The ratios ranged from a minimum of 0.3 to a maximum of 0.7 with a mean of 0.5, indicating that PM_2.5 contributed significantly to PM₁₀ in all samples. The PM mass ratios for the four sites representing background, urban, residential and industrial conditions are summarized in Table IV. The mass ratio PM_2.5/PM₁₀ gives an indication of the relative importance of natural and anthropogenic sources to PM (Querol et al., 2004). A low PM_2.5/PM₁₀ mass ratio indicates a relatively large contribution from natural sources since they tend to dominate in the particle size range 2.5–10 \xm. The monthly mean values of PM_2.5 and PM₁₀ are shown in Figure 4.

Basically, the seasonal variation is similar for all sites, with the annual low occurring during the summer months. The PM_2.5 concentrations partially follow the pattern observed for PM₁₀ with low concentrations during summer season. The increase in PM_2.5 concentration after the summer season is, however, more pronounced than for PM₁₀. The higher values of PM₁₀ in April and May may be due to the dust storm episode from 11 to 14 May 2001, as shown in Figures 5a and 6a. Thus, the main explanations for the seasonal variation may be deduced from these figures.

Figure 5 shows the seasonal variation on numbers of dust storms in GC (Fig. 5a) and the numbers of detected fires due to burning of waste from harvested rice in the Nile delta (Fig. 5b) The fires were detected with the moderate resolution imaging spectroradiometer (MODIS) aboard the Terra satellite, with 1 km resolution by monitoring radiation in the 3.9 (im channel that saturates at 500 K. During night the detection system also uses the 1.65 and 2.15 (im channels. The periods of dust storms (March–April) and waste burning (September–November) can be linked to the seasonal variation of PM₁₀ and PM_2.5 shown in Figure 4. Thus, aerosols from dust storm events and waste burning enhanced the levels of PM_2.5 and PM₁₀ significantly. Coarse particles from dust storm events contribute to increase the levels of PM₁₀, most of this particles fall back to ground with dry deposition and sedimentation, while the fine and accumulated ones are transported in the atmosphere to play the direct effect on radiation (Zakey et al., 2006). Aerosols from waste burning produces finer particles that may contribute more to PM_2.5. As an example, Figure 6 shows the episodic nature of these two sources, where e.g. the PM₁₀ levels can reach extreme values during some hours. Both, the wind direction and wind speed are crucial parameters for these severe conditions. In addition to these two seasonal effects, low winter–time temperatures often result in stable weather conditions that aggravate the effects of particle emissions from urban traffic and industrial activities as shown in Figures 7 and 8.

Figure 7 shows the wind direction frequency distribution for selected sites. The most prevailing wind direction is from north in GC area, but this direction is slightly shifted north–west in delta. Wind from north occurred during 65% of the time at Abbasiya (36), 74 at Tabbin (7), 49 at Shoubra (20), and 66% at Giza (30). The highest wind speed occurred at Tabbin, Shoubra and Giza, exceeding 10ms^–1.

Table V gives an overview of the correlation coefficients (r²) of the monthly average values of PM₁₀ and PM_2.5 between all sites. Most sites show a positive correlation because they are either responding to regional sources affecting the whole area, like waste burning or dust storms, or to well distributed point sources like traffic. As can also be seen from the analysis of the lead data, the industrial sites are not as well correlated as the other due to increased numbers of potential point sources of particulate matter. Especially the correlation coefficients between Abu Zabal (37) and most of the other sites are low. This site is up–wind of GC and the low correlation stresses further that the site is mostly exposed to local industrial activities.

3.2 Lead concentrations

Figure 9 shows the average concentrations of lead in PM₁₀ (Pb₁₀) and in PM_2.5 (Pb_2.5) observed at the 17 measurement sites during 2001–2002. The average Pb₁₀ concentrations are between 1 and 2 µg m^–3 at most sites, with a couple of exceptions showing higher average values, i.e. the industrial sites. Thus, the lead concentrations at most of the sites exceed the EGL/94 annual limit of 1 µg m^–3. The monthly variation of Pb₁₀ shows higher values at the industrial sites (ranged from 6 to 16 times the EGL/94 limit), while the others urban, residential and background sites recorded values around the EGL/94 limit, the same behavior is noticed for Pb_2.5 as shown in Figure 10.

It was concluded that Pb is associated with the fine fraction since the Pb_2.5 concentrations are comparable to the values of Pb₁₀. The ratios of Pb_2.5 to Pb₁₀ presented in Table IV are high with an average of 85%. Since associated to the fine fraction the Pb emissions can spread over a larger area, thus affecting a significant part of the population. It stands clear that the air quality in the region can benefit significantly if the Pb emissions from the industrial point sources are reduced. The yearly average concentration of above 1 µg m^–3 for all sites within the GC area, where there lives 15 million people, is giving an indication that 74.9% of the urban sector, 100 of the industrial sector, 43 of the residential sector and 12% of the background sector are facing lead exposure. The lead sources and consecutive exposure to the inhabitants in GC has further been evaluated and presented in a report by the Egyptian Environmental Affair Agency (EEAA, 2002). In this report they conclude that the major industrial sources of lead were from diesel combustion and lead smelters. Furthermore, it was noted from data in that report that there are 100% of people living in industrial areas which are directly affected by these elevated Pb levels.

Lead may be emitted from several sources, including fuel and motor oil combustion, brake wear, and re–suspension of enriched road dust. Figure 11 indicates that the sources of lead in GC are: 1) Mazout (diesel) combustion, 2) Secondary lead smelting, 3) Secondary copper processing, 4) Lead–acid battery production, and 5) Portland cement manufacturing. The ratio from the Portland cement manufacturing, secondary copper production and lead–acid battery production was very small, and a significant ratio was recoded from secondary lead smelting. The lead from mazout is the dominant source of Pb in the GC as shown in figure 9, contributing up to 43% of PM₁₀ Pb at the industrialized.

3.3 Comparison with other studies

Table VI shows values of PM_2.5 and PM₁₀ from some previous studies. Abu–Allaban et al. (2002) presented measurements from 1999. These values are comparable to the present results. However, the industrial areas recorded significantly lower values comparing to the previous measurements due to the improvements of some industrial activity, for example, the filter systems of the cement industry and the decreasing number of smelter workshops.

In comparison to measurements from Lebanon, Italy, Greece and Spain, the values of annual PM₁₀ and PM_2.5 from the GC sites are much higher and are due to the larger population in Cairo. Concentrations obtained at some traffic sites, e.g. Milan, Italy, can reach and exceed the levels obtained in Cairo area. However, in most European cities the abatement of urban pollution has given effects, and significant lower levels are present, e.g. Athens, Zurich and London. Table VI also includes measurements from some megacities in the world. Even if Cairo is not the most polluted megacity in the world, the location of Cairo in a desert area has an effect on the air pollution levels from the additional dust source.

 

4. Concluding remarks

Two years measurements of PM (PM₁₀, PM_2.5) in GC in different environments (industrial, urban, residential and background) have been evaluated. The results indicated that the average concentration of PM₁₀ (PM_2.5)was 1.3 (1.6), 1.8(1.7), 1.6(1.6), 1.6 (1.4) times lower in summer than in winter at industrial, urban, residential and background sites, respectively. The low values recorded during the summer season are due to the absence of dust episodes and waste burning in combination with good dispersion. Generally, the severe air pollution situation in GC is enhanced by the naturally occurring dust storms and the anthropogenic waste burning in the Nile delta. Both of these issues are regional in character and may influence the climate in the region, where the aerosols are a key factor of radiative forcing and cooling of the atmosphere over Europe and Africa (Solmon et al., 2006; Zakey et al., 2006). In the perspective of human health, the fine aerosols PM_2.5 are more effective in causing respiratory illness and premature death than larger aerosols due to their ability to penetrate deeper into the lung (Kaiser, 2005).

The high Pb content in particle samples can be directly related to industrial activities where the sources of combustion of mazout, and lead smelting can be traced and abated. This will reduce the Pb exposure for a large part of the population in the area. The homogeneously distributed fine particle fraction from urban sources present in the GC area is mostly from traffic. The observed reduction of Pb content in the urban aerosol due to phase out of leaded petrol shows the effect on air quality on implementation of environmental actions.

 

Acknowledgements

This work was supported by MISTRA, the Swedish Foundation for Strategic Environmental Research. The Charmin board of Egyptian Meteorological Authority and the Egyptian Environment Affairs Agency are acknowledged for supporting and promoting this evaluation by supplying data.

 

References

Abu–Allaban M., A. W. Gertler and D. H. Lowenthal, 2002. A preliminary apportionment of the sources of ambient PM₁₀, PM_2.5, and VOCs in Cairo. Atmos. Environ. 36, 5549–5557.        [ Links ]

Ali E. A., M. M. Nasralla and A. A. Shakour, 1986. Spatial and seasonal variation of lead in Cairo atmosphere. Environ. Pol. Series B–Chemical and Physical 11, 205–210.        [ Links ]

Baldasano J. M., E. Valera and P. Jimenez, 2003. Air quality data from large cities. Sci. Total Environ. 703, 141–165.        [ Links ]

Belal M. and M. Saleh, 1978. Uptake of lead near roads in Egypt. Atmos. Environ. 12, 1561–1562.        [ Links ]

Biswas S. K., S. A. Tarafdar, A. Islam and M. Khaliquzzaman, 2003. Impact of unleaded gasoline introduction on the concentration of lead in the air of Dhaka, Bangladesh. J. Air Waste Manag. Assoc. 53, 1355–1362.        [ Links ]

Chaloulakou A., P. Kassomenos, N. Spyrellis, P. Demokritou and P. Koutrakis, 2003. Measurements of PM₁₀ and PM₂.₅ particle concentrations in Athens, Greece. Atmos. Environ. 73, 649–660.        [ Links ]

Egyptian Environmental Affair Agency (EEAA), 2002. Report–1999 Baseline lead emissions inventory for the Greater Cairo Area; Cairo Air Improvement Project (CAIP), Chemonic International, Inc. USAID/Egypt, Office of Environment USAID Contract No. 263–C–00–97–00090–00.        [ Links ]

El–Tahir H. M., E. S. Lindgren and F. I. Habbani, 2004. Elemental characterization of airborne particles in Khartoum, Sudan. X–Ray Spectrom. 34, 144–152.        [ Links ]

Fang G. C., C. N. Chang, C.–C. Chu, Y. S. Wu, P. P. C. Fu, I. L. Yang, I. L. and M. H. Chen, 2003. Characterization of particulate, metallic elements of TSP, PM_2.5 and PM_2.5–10 aerosols at a farm sampling site in Taiwan, Taichung. Sci. Total Environ. 308, 157–166.        [ Links ]

Gehrig R. and B. Buchmann, 2003. Characterizing seasonal variations and spatial distribution of ambient PM₁₀ and PM_2.5 concentrations based on long–term Swiss monitoring data. Atmos. Environ. 37, 2571–2580.        [ Links ]

Hassanien M. A., J. Rieuwerts, A. A. Shakour and A. Bitto, 2001. Seasonal and annual variations in air concentrations of Pb, Cd and PAH's in Cairo, Egypt. Int. J. Environ. Health Res. 11, 13–27.        [ Links ]

Harrison R. M., A. M. Jones and R. G. Lawrence, 2004. Major component composition of PM₁₀ and PM_2.5 from roadside and urban background sites. Atmos. Environ. 38, 4531–4538.        [ Links ]

Kamal A. A., S. E. Eldamaty and R. Faris, 1991. Blood lead level of Cairo traffic policemen. Sci. Total Environ. 105, 165–170.        [ Links ]

Kaiser J., 2005. Mounting evidence indicts fine–particle pollution. Science 307, 1858–1861.        [ Links ]

Lonati G., M. Giugliano, P. Butelli, L. Romele and R. Tardivo, 2005. Major chemical components of PM_2.5 in Milan (Italy). Atmos. Environ. 39, 1925–1934.        [ Links ]

Molina M. J. and L. T. Molina, 2004. Megacities and atmospheric pollution. J. Air Waste Manag. Assoc. 54, 644–680.        [ Links ]

Noweir K. H., 1990. Study of the role of airborne lead in food chain of crops grown around a main highway in Egypt. J. Egyptian Public Health Assoc. 65, 427–437.        [ Links ]

Querol X., A. Alastuey, A. Lopez–Soler, F. Plana, A. Mesas, L. Ortiz, R. Alzag, J. M. Bayona and J. de la Rosa, 1999. Physico–chemical characterization of atmospheric aerosols in a rural area affected by the aznalcollar toxic spill, south–west Spain during the soil reclamation activities. Sci. Total Environ. 242, 89–104.        [ Links ]

Querol X., A. Alastuey, C. R. Ruiz, B. Artinano, H. C. Hansson, R. M. Harrison, E. Buringh, H. M. Brink, M. Lutz, P. Bruckmann, P. Straehl and J. Schneider, 2004. Speciation and origin of PM₁₀ and PM₂.₅ in selected European cities. Atmos. Environ. 38, 6547–6555.        [ Links ]

Robaa S. M. and Y. Hafez, 2002. Monitoring urbanization growth in Cairo City. J. Eng. Appl. Sci. 49, 667–679.        [ Links ]

Robaa S. M., 2003. Urban–suburban/rural differences over Greater Cairo, Egypt. Atmósfera 16, 157–171.        [ Links ]

Rodes C. E., M. M. Nasralla and P. A. Lawless, 1996. An assessment and source apportionment of airborn particulate matter in Cairo, Egypt. Activity Report No. 22 prepared for the USAID mission in Egypt under EHP activity No. 133–RCm delivery order No. 7.        [ Links ]

Rodríguez S., X. Querol, A. Alastuey, M. M. Viana, M. Alarcon, M. Mantilla and C. R. Ruiz, 2004. Comparative PM₁₀–PM_2.5 source contribution study at rural, urban and industrial sites during PM episodes in Eastern Spain. Sci. Total Environ. 328, 95–113.        [ Links ]

Roy D. P., J. S. Borak, S. Devadiga, R. E. Wolfe, M. Zheng and J. Descloitres, 2002. The MODIS Land product quality assessment approach. Remote Sensing Environ. 83, 62–76.        [ Links ]

Solmon F., F. Giorgi and C. Liousse, 2006. Aerosol modeling for regional climate studies: Application to anthropogenic particles and evaluation over a European/African domain, Tellus B, 15 58, 51–72.        [ Links ]

Shaka H. and A. Saliba, 2004. Concentration measurements and chemical composition of PM_10–2.5 and PM_2.5 at a costal site in Beirut, Lebanon. Atmos. Environ. 38, 523–531.        [ Links ]

Sharma M. Y. N., V. M. Kiran and K. K. Shandilya, 2003. Subset statistical modelling of atmospheric sulfate. Clean Air Env Quality 38, 37–41.        [ Links ]

Watson J. G. and J. C. Chow, 2001. Source characterization of major emission sources in the Imperial and Mexicali Valleys along the US México Border. Sci. Total Environ. 276, 33–47.        [ Links ]

Zakey, A. S., and M. A. Omran, 1997. 1st LAS/WMO International Symposium on Sand and Dust Storms, WMO Programme on Weather Prediction Research Report Series Project No. 10, World Meteorological Organization (WMO), Technical Document No. 864.        [ Links ]

Zakey A. S., F. Solmon and F. Giorgi, 2006. Implementation and testing of a desert dust module in a regional climate model, Atmos. Chem. Phys. 6, 4687–4704.        [ Links ]