Modernization is a concept the globe is still coming to grips with. 200 years ago the world was a different place, and mankind existed in relative simplicity. Automobiles, air conditioners, and manufactured goods were luxuries beyond comprehension.
Day to day, humans had little impact on the environment of the globe as a whole. The dawn of the industrial revolution changed that simplistic existence dramatically and gave rise to the cities in which we live today. Prior to the 1800's London was the largest city in the world with a population close to one million people. Today the world's largest city, Tokyo Japan has an urban population nearly thirty four times the size. The effects of living in these urban centers is still being determined. It was only in 1952 that the word "smog" was coined, combining the words smoke and fog to describe the soup that enveloped London. That year it is estimated that somewhere between 4,000 and 12,000 people died from the "Great Smog" due to high concentrations of air pollution.
Air quality was a concept not yet grasped. Only after thousands perished was it understood that a city's population pays a price for modern living. Measures have since been taken to protect the air in major cities, and while immediately toxic combinations have been pinpointed and carefully controlled, the long term health effects of what remains is still under study. And the question must be raised, what are we releasing into our air?