Air pollution is defined by the Wor

Air pollution is defined by the World Health Organisation as:“contamination of the indoor or outdoor environment by any chemical,physical or biological agent that modifies the natural characteristics of the atmosphere” [1]. Seinfeld and Pandis proposed an extended definition,stating that: ”air pollution is the presence in the air of one or more substances at a concentration or for duration above their natural levels, with the potential to produce an adverse effect” [2]. This implies that some of the substances that are regarded to be “air pollutant”, are naturally present in the air [3]. Those air pollutants have both natural and anthropogenic origin. Indeed, anthropogenic activity has had, and is still having, a dominant role in the increase of air pollutants to levels that yield adverse impact on human health and on the environment. Exposure to air pollution has been reported to be as the 5th ranking human health risk factor worldwide [4]. Several studies also recognised an association between air pollution and the climate changes that we are idly witnessing [5].