Carbon dioxide is for suckers. If you really want to do some damage to the environment, sulfur hexaflouride is where it's at. According to Pollution Online (which, despite its name, is actually against pollution), one pound of SF6 has the same potential global-warming impact as 11 tons of CO2. Sulfur hexaflouride is used in high-voltage electrical equipment. If inhaled, it acts like antihelium, and, according to Wikipedia, makes one "sound like the god of hellfire." Finally, this dangerous (and potentially hilarious) gas is odorless, colorless, nontoxic, nonflammable, and extremely difficult to detect.
That's enough of a chemistry primer. The big news is you (if "you" are a master electrician or environmental engineer with deep pockets) can now buy a camera that can detect the gas. Infrared-imaging company FLIR Systems recently revealed the GasfindIR-LW, a thermal imaging camera that can detect SF6 and 20 other environmentally perilous gasses. If you ever wanted to hunt down acetylchloride; allyl flouride; or Freons 11, 12, 112, 113, or 114, the GasfindIR-LW is just the device you need.
Of course, like most fun toys, it's a strictly specialized piece of scientific equipment. The camera is a four-pound box that can capture footage only at 320x240 resolution. You can't exactly find it at your local BestBuy or Circuit City, either; this sort of device can cost several thousand dollars and must be bought either directly from the manufacturer or a very small number of professional supply stores.
Still, if you want to spend the time and drop the cash, it's a great way to find out just how dangerous the air around you really is.