Dependence of urban air pollutants on meteorology
Introduction
To date nearly 3000 different anthropogenic air pollutants have been identified most of them organic (including organometals). Combustion sources, especially motor vehicles, emit about 500 different compounds (Fraser et al., 2003). However, only for about 200 of the pollutants have the impacts been investigated, and the ambient concentrations are determined for an even smaller number (Dzubay and Mamane, 1989, Van Borm et al., 1990, Paoletti et al., 1991, Paoletti et al., 1999, Al-Rajhi et al., 1996, Esteve et al., 1997, Kasparian et al., 1998, Chan et al., 1999, etc.). To better understand the effects that exposure to acid aerosols has on humans, epidemiologic air pollution studies have begun to characterize the spatial and temporal distribution of acid aerosols (Suh et al., 1992, Purdue et al., 1992, Samet et al., 2000, Pope et al., 2002). But to fully understand the processes responsible for the spatial and temporal distribution of acid aerosols requires analysis of local and regional meteorology; especially wind direction; wind speed; turbulence; and atmospheric stability (Michael, 1997, Hien et al., 2002, Laakso et al., 2003). Chemical reactions also depend on ambient weather conditions because they are influenced by short-wave radiation; air temperature; and air humidity. Along with chemical reactions, dispersion and dilution processes result in ambient air pollution which shows concentrations of different substances varying with regard to time and space.
Although the relationships between synoptic meteorology and air pollution have been investigated for pollutants such as ozone (Comrie, 1990, Comrie, 1992, Comrie, 1994, Eder et al., 1994), SO2 (Kalkstein and Corrigan, 1986), NO2 (Davis and Kalkstein, 1990), greenhouse gas induced global warming (Kalkstein et al., 1990), and even visibility (Davis, 1991), we still have very little information about the dependence of urban aerosol on the city's geographical, geological and meteorological conditions. Several works have been done studying air pollution in Great Cairo area, where the sources of air pollutants have been identified (Hagazy, 1961, Salam, 1967, Nassr-Allah, 1968, Salam and Sowelim, 1976, El-Taieb, 1981, Mosalam, 1986, Abdel-Rahman et al., 1988, El-dahab, 1990, El-Hussainy and Sharobiem, 2002). In view of the above discussion, it is necessary to define the status of ambient air quality due to the presence of different pollutants in the environment of Cairo. This paper examines the temporal relationship between meteorological parameters and urban air pollutants, helping to fill a void in research into the relationships between the atmospheric circulation, local meteorology, and concentrations of tropospheric air pollutants.
Section snippets
Apparatus and measurements
Different organizations (e.g., Centre for Environmental Hazard Mitigation, CEHM at Cairo University; the Institute of Graduate Studies and Research, IGSR at Alexandria University; and the Egyptian Environmental Affairs Agency, EEAA) have been monitoring ambient air quality at 14 sites distributed over the whole territory of Great Cairo area. In general, sites characteristics are different representing industrial, traffic, urban, residential and background. Not all parameters are being measured
Site and climate dependence of tropospheric aerosol collection
Like most subtropical regions along the North African desert, Cairo city has mainly two seasons: summer (May–mid-October) and winter (December–February), with a very short spring (March and April) and autumn (October and November). The average summer temperature is 29 °C, while that of winter is 16 °C with an average difference between day and night of 10 °C. This great temperature difference promotes the formation of dew at dawn as the relative humidity of the air becomes generally high,
Chemical and mineralogical composition
The question of the existence and trace power of regional elemental characteristics reflecting the structure of emission sources at a given location has been treated in a number of publications. As summarized in some reference papers (Pacyna et al., 1984, Tsoar and Pye, 1987, Pye, 1992, Church et al., 1990, Koltay, 1990) single element traces or ratios of elemental concentrations can be used for studying the nature of main emission sources in the region as well as for pinpointing the sources
Trends of air pollutant concentrations
The diurnal pattern of O3 (see Fig. 4) is characterized by maximum concentration in the afternoon and minimum concentration during early morning hours. The increase in O3 during day is basically due to photo-oxidation of precursor gases, like CO, CH4, and hydrocarbons in the presence of sufficient amount of NOx. Being an urban site, NO concentrations at Cairo are generally found to be well above the threshold level for O3 production. For example, the well-known photo-oxidation cycle of CO can
Contribution of wind aspects to concentration of air pollutants
The prevailing winds, which may transport moisture or aerosol particles from distant sources, play a major role on the seasonal variation of turbidity. A correlation analysis indicates significant negative correlation between total urban concentration and wind speed data. Such behavior is plausible for non-crustal elements where transport effects increased by higher wind speed, give an explanation for the clear-up of the local air. An investigation into the effect of wind direction aspects on
Conclusion
The aim of the present study was to establish which meteorological parameter influences the elemental concentrations to characterize the short range transport of traffic-related airborne particles and to standardize the concentrations with respect to the meteorological parameters. On the basis of the present study, it can be concluded that wind and relative humidity are shown to be the most important meteorological parameters influencing the behavior of air pollutants, which are further
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