Every vehicle that recycles its air, ranked by how much you'd want to be stuck inside
with smelly passengers.

  1. Commercial airliner
    Despite what most people think, airline passengers aren't all breathing in each other’s coughs and farts for the whole flight: The air is actually drawn in from outside by the engines, then pressurized and circulated throughout the cabin. lt‘s probably much cleaner than your typical office air, too, being completely refreshed about 20 times an hour (compared to 12 for the average office).
  2. Submarine
    Submarines create oxygen from seawater via a $1 million electrolysis machine (not to be confused with the hair-removal process). The water is boiled, the steam condenses into fresh water and an electrical current separates the H2 from the O. All the exhaled CO2, meanwhile, is removed by a "scrubber," which uses soda lime to filter out the carbon. Unfortunately, these smell terrible—like diesel mixed with sulphur-and the stink is inescapable inside a submarine.
  3. Spacecraft
    As well as scrubbers, the International Space Station has a cool device called the Sabatier System, which takes the hydrogen separated during electrolysis and combines it with CO2 to make more water. (There are also charcoal filters that absorb the methane from farts and the ammonia from urine.) While space technology is fancy, the lifestyle ain't: Astronauts say the lSS smells like garbage and body odor. And watch out for mouse poop floating by, as the mice sometimes escape from the many science experiments aboard the station.
  4. Subway train
    Here's a gross fact: 15 percent of the airborne matter in subway-car air is human skin. There are also double the normal levels of airborne fungi—from the rotting wood of railroad ties- plus high levels of metal dust from the wheels and brakes, which are kicked up every time the train comes to a screeching halt at the platform. The air is filtered a little by air conditioning, but all things considered, you're probably better offdodging mousetronaut turds.
  5. Garbage truck
    A Danish study from 2016 found that bacterial and fungal concentrations inside garbage truck cabs were 11.7 and 111 times higher, respectively, than outside the truck. This, they concluded, is because garbage truck drivers don‘t always wash their outer work clothes. Since they often drive several different trucks, these pathogens are then spread throughout the fleet. That flight home doesn't sound so bad now, huh?