Cars are the main source of noise pollution and air pollution in cities, nothing else comes to mind. Factories and such were either moved to other continents, o

Cars are the main source of noise pollution and air pollution in cities, nothing else comes to mind. Factories and such were either moved to other continents, or zoning was updated to ban them in population centers. I guess fossil fuel combustion contributes as well, but that's on its way to becoming less of a problem.