Until the 1940s, efforts to control air pollution in the United States were limited to a few municipal ordinances and state laws regulating smoke (Chapter 4). In the United Kingdom, regulations were limited to the Alkali Act of 1863 and some relatively weak Public Health Bills designed to abate smoke. Regulations in other countries were similarly weak or nonexistent. The main reason for the lack of regulation in polluted cities was that the coal, oil, chemical, and auto industries, the ultimate sources of much of the pollution, had political power and used it to resist efforts of government intervention (e.g., Section 4.1). Because the long-term health effects of pollutants in outdoor concentrations were not well known at the time, it was also difficult for public health agencies to recommend the banning of a pollutant, particularly in the face of political pressure from industry and arguments that such a ban would hurt economic growth (e.g., Midgley's defense of tetraethyl lead in Section 3.6.9). In the late 1940s through mid-1950s, damage due to photochemical smog in the United States was sufficiently apparent that the federal government decided to take steps to address the problem. Similarly, deadly London-type smog events in the United Kingdom spurred government legislation in the 1950s. Today, many countries have instituted air pollution regulations. Nevertheless, regulations in most countries are still weak, resulting in severe pollution problems. Many countries, for instance, continue to allow tetraethyl lead in their gasoline and do not require catalytic converters in automobiles.