 Complete the following phrase:  Serious smog events had become a common occurrence in London since the second half of the 19th Century, with industrialisation causing an increase in air pollution that often killed hundreds of the citys inhabitants when it amassed in great quantities during winter months. Since the Second World War, severe smog episodes had occurred in November 1948 causing an estimated 700 to 800 deaths, January 1956 1,000 deaths, December 1957 750 deaths and January 1959 over 200 deaths. The 1952 