"The word thus coined is a contraction of smoke and fog — 'smog' — and its introduction was received with applause as being eminently expressive and appropriate. It is not exactly a pretty word, but it fits very well the thing it represents, and it has only to become known to be popular."
Common to all three tragedies were two key elements. First, large factories in each area had been spewing enormous amounts of pollutants into the air, the most deadly being sulfur dioxide. And second, Mother Nature came calling in the form of something called a temperature inversion.