In 1948, smog filled the Monongahahela Valley in western Pennsylvania. Damaging oxides of nitrogen, halogen acids, zinc and lead claimed 20 lives with 2,000 afflicted with respiratory disorders.  Fog and industrial pollution created the worst episode of smog in London from January 5th through the 9th in 1952.  Stagnant air over the four day period found sulfur dioxide and particulate concentrations reaching deadly levels.  The smog was so thick that Londoners couldn't see their hands with outstretched arms, traffic stopped and only the blind could navigate. Close to 100,000 residents became sick as deaths from bronchitis and influenza increased ten times leaving 4,000 dead. Four years later, Parliament enacted the British Clean Air Bill as the burning of bituminous coal was banned.  Here's another tidbit...Early war ships were equipped with iron cannon balls, stacked next to the cannons. A method was devised to stack 30 cannon balls in a squared “pyramid” configuration with 16 balls on the bottom to one on top. The design saved space however the movement of the ship sent the balls rolling all over the deck and sometimes overboard. The solution was a metal plate called a “Monkey” that included 16 round indentations. To prevent the iron balls from rusting, the “Monkey” was unfortunately made of brass and brass contracts faster than iron in cold weather. When below freezing conditions occurred, the brass indentations shrunk and the iron cannonballs would lift off the “Monkey.” Thus the expression, ”its cold enough to freeze the (expletive deleted) off the Brass Monkey.”