While many factors can diminish a city's quality of life, one literally takes residents breath away: smog. Traffic, industrial pollution, weather patterns and geography can turn a perfectly lovely city into a very hazy place. Cleaning the air requires a clear understanding of the pollution's sources, and photonics offers a number of techniques that can provide some clues.The metropolitan area surounding Athens, Greece, is among the world's cities with a summer smog problem. In 1994, the European research project Mediterranean Campaign of Photochemical Tracers EM DASH Transport and Chemical Evolution visited Athens to measure the air quality and observe the city's meteorology. The researchers hoped to improve and verify the meteorological and atmospheric models that work on a micro- and mesoscale. Among their techniques was a laser-based method that provided useful information about source pollutants: differential absorption lidar.