Since the start of history, the fundamental requirements of human civilization have been spoken about to include food/water, housing, and clothes. Of course, as civilizations have evolved, the human need and its expression have also increased. However, the crux of existence has always been accepted as the above. It has been only in the recent years that the human need of breathing clean air has emerged as a still more crucial challenge.

It is a reflection of the times that we are living in. You ascribe it to polluting industrialization or unsustainable construction, excessive traffic or plain and simple overpopulation and sanitation, the truth is that something as elementary as the air we breathe, something that from primeval times was taken for granted hence never considered as daunting, is in the last decade or so being perceived as the most formidable threat to the salubrity of our civilization.