Smithsonian: When Beijing issues a red alert closing schools and restricting traffic because air pollution is ten times the World Health Organization's recommended level, it seems like another symptom of modern life.
But fouled air has a long and unhealthy history, and the deadly haze that plagues Beijing, Delhi, Mumbai and Karachi, among other cities, has been around in one form or another for thousands of years.
First it was wood fires in ancient homes, the effects of which have been found in the blackened...