Dependence of urban air pollutants on meteorology

Abstract

Dependence of air pollutants on meteorology is presented with the aim of understanding the governing processes pollutants phase interaction. Intensive measurements of particulate matter (PM₁₀) and gaseous materials (e.g., CO, NO₂, SO₂, and O₃) are carried out regularly in 2002 at 14 measurement sites distributed over the whole territory of Great Cairo by the Egyptian Environmental Affairs Agency to assess the characteristics of air pollutants. The discussions in this work are based upon measurements performed at Abbassiya site as a case study. The nature of the contributing sources has been investigated and some attempts have been made to indicate the role played by neighboring regions in determining the air quality at the site mentioned. The results hint that, wind direction was found to have an influence not only on pollutant concentrations but also on the correlation between pollutants. As expected, the pollutants associated with traffic were at highest ambient concentration levels when wind speed was low. At higher wind speeds, dust and sand from the surrounding desert was entrained by the wind, thus contributing to ambient particulate matter levels. We also found that, the highest average concentration for NO₂ and O₃ occurred at humidity ≤ 40% indicative for strong vertical mixing. For CO, SO₂ and PM₁₀ the highest average concentrations occurred at humidity above 80%.

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.