字幕列表 影片播放 列印英文字幕 [Trace]Gotta get ready. That hole in the ozone layer you know that's some serious stuff. [Julian] Hey that's not a thing anymore [Trace] WHAT? IT'S GONE?! Howdy chlorofriendocarbons, you've found your way to DNews, thanks for that! Welcome! I'm Trace. If you are a Millennial, you've probably spent your whole life hearing about the "hole" in the ozone layer. Before you can understand the hole, though, you gotta know what the ozone layer is. The ozone layer isn't really its own thing, instead 90 percent ozone floats around the stratosphere: about 6 to 30 miles above our heads. Ozone is three oxygen atoms linked together1,3, Oh-three. When in the stratosphere, ozone absorbs harmful UV-B radiation, protecting us and other life here on the ground (in the troposphere). In the late 19th and early 20th centuries, people were just beginning to harness the power of refrigeration using toxic gasses like ammonia, methyl chloride, and sulfur dioxide. In 1928, an enterprising inventor at General Motors created a non-toxic chemical for refrigeration called CFC -- chlorofluorocarbon. It was patented as Freon by DuPont, and sold in air conditioners, fridges, bug sprays, spray paints, hair conditioners, and healthcare products. At it's peak companies were making a million metric tons of CFCs every year. Then, in a 1974 study in Nature found this great nontoxic refrigerant was wreaking havoc on the atmospheric ozone layer. Sure, at sea level, CFCs are nontoxic and safe for humans, but if they get into the upper atmosphere, they're subject to photodissociation: where UV radiation breaks a Chlorine atom off the CFC! If that free chlorine finds a molecule of ozone (O-three) it will react with it, destroying the ozone by ripping off one of its oxygen atoms to make Chlorine Monoxide, leaving regular old O2, or oxygen, in its wake. Then the Chlorine Monoxide gets hit by UV and broke up again… so it has to find another O3 molecule to stabilize it…and the cycle repeats itself. It's bad. In 1977, we were studying the ozone layer and it was fine. By 1981, there were hints something was amiss. Then in 1984, scientists suddenly registered a giant hole in the ozone layer. They published their findings and in 1987, the Montreal Protocol was signed, beginning the phasing out CFCs shortly thereafter. Meanwhile even though the house was clearly on fire, Du Pont and other companies insisted everything was fineand fought tooth and nail to keep CFCs legal. But they finally relented after scientific evidence became indisputable. A looming environmental disaster that pitted corporations against the scientific community… where have I heard that before? Though CFCs can hide in the atmosphere for 40 to 150 years, without the emission of new CFCs, eventually that free chlorine cycle will stop. If the chlorine runs into some methane up there, it would break it up forming hydrogen chloride which is stable enough to rain down to Earth. In 2015, about 30 years after the Protocol was signed, the ozone hole reached the largest size EVER. But since that peak (due mostly to volcanic eruptions that sprew bromine, another Ozone depleting gas), scientists have finally started to see the ozone layer repair itself! A study published in Science this year found the hole had decreased in size from the year 2000, and most of that decrease was specifically because of the Montreal Protocol!! International Policy, for the win! Without the chlorine wafting up into the stratosphere, ozone was able to form naturally -- when UV light breaks up regular old oxygen from O2 into O3. Without the chlorine to mess it up, this process could restart! It can still be messed up by volcanic eruptions, but overall without our meddling, the ozone layer may someday be back to normal! Based on this new study, the Ozone layer might be back to 1980 levels by 2040! You can actually see how the Ozone layer is doing right now, on NASA's website! We'll put the link in the description for you. Of course, this is science, so we can't have all happy endings. We still need AC and fridges, and the replacement gas, HFCs, are a potent greenhouse gas. So now, global warming is a concern. Sigh. We can never win. But hey, at least that thing we fought for as kids is getting better, right? But...why is there air in the first place?