Our crew went all the way to the west to observe London and Los Angeles, where had been affected by heavy air pollution. We restudy the history and try to find solutions for current air pollution problem. We revisit the severely affected areas at that time, interview local experts, and talk to policy makers in these two cities. In addition, the programme discusses how to use new technology to improve our ability in prevention and thus change the current situation. Walking from the smoggy history, the battle never stops.