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

摘要

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 200 1 2002 in the two size fractions PM2.5 and PM10 at 17 sites representing different activities (industrial, urban, residential and background condition). The PM concentrations were generally high, with yearly average PM2.5 and PM10 values of 85 12 and 170 25 mu g/m(-1), 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 PM2.5/PM10 ratio was recorded in the urban sector (0.59) while the lowest ratio was recorded in the residential sector (0.32). The PM25 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 PM2.5 (Pb-2.5) and PM10 (Pb-10) varied between 0.4 and 1.8 +/- mu g 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(-1) 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-Kbeima (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.