This study draws on London’s long experience with air pollution in order to improve our understanding of the overall effects of pollution exposure and how and why these effects evolve as locations develop. I compare uniquely detailed new mortality data covering 1866 to 1965 to the timing of London’s famous fog events, which trapped emissions in the city. I show that air pollution was a major contributor to mortality in London over this period and that it interacted strongly with specific infectious diseases. As a consequence of this interaction, reductions in the infectious disease burden substantially altered the health costs of pollution.

Can a temporary economic shock to an important local industry influence long-run city population? To answer this question I study the large temporary shock to British cities caused by the U.S. CivilWar (1861–1865), which reduced cotton supplies to Britain’s important cotton textile industry. I show that this event temporarily reduced the growth rate of cities specializing in cotton textile production, relative to other English cities, and led to a persistent change in the level of city population.