Dublin is known as a city where you can enjoy a few pints of Guiness, get a warm welcome from the locals and hear lively traditional music drifting out of pubs and into the city air. But it's not just music floating on the breeze. The air of Dublin also contains cannabis, poppy, even magic mushrooms -- at least their DNA. That's according to a new study that reveals the power of DNA, vacuumed up from the air, which can track everything from elusive bobcats to illicit drugs. "The level of informa...