Pollution monitoring equipment. Technician operating a pump and probe LIDAR (Light Detection and Ranging) apparatus to measure air pollution levels. This equipment fires two laser beams (at left) into the sky. The first beam generates a strong concentration of hydroxyl radicals at a given point in the atmosphere. The second beam measures how long these highly reactive radicals survive. Hydroxyl radicals will be quickly destroyed by the large hydrocarbons found in a polluted atmosphere. Hence, if the radicals have a short lifetime, this indicates a highly polluted atmosphere. Photographed at Lausanne Polytechnic (EPFL), Switzerland.