Air quality index (AQI) is a quantitative tool through which air pollution data can be reported, providing information on how clean or polluted the air is. Several countries employ some type of air quality index to communicate the quality of their air. Some of these systems rely on relating measured (monitored) or predicted concentrations of air pollutants (results of modelling system). In this paper, a methodology for developing an air quality index (AQI) for Tunisia is presented. This index is a national air quality rating system based on the national ambient air quality standards. It is based on the new project of Tunisian ambient air quality standards. The methodology applied in the calculation of this index can be applied for any country with replacing specific standards. Thanks to this index, the ambient air quality in Gabès was assessed during 2008 and we have made a comparison between the level of air pollution in Gabès and this level in other three regions, Sfax, Sousse and Manouba, in Tunisia. The result shows that 31% of the calculated AQI values in Gabès are categorised as 'poor' and 'bad'.
Keywords: air quality index, AQI, Tunisia, air quality monitoring, air quality standards, air pollution