now back to uh initial survey on environmental knowledge question five the Antarctic ozone hole is responsible for melting the ice cap letting in excess heat from the Sun both of those together or increased skin cancer almost every single one of you answered with the same choice those first two melting the ice Gap Plus letting in heat from the Sun guess what you're all wrong I knew that was going to happen by the way it always does here's the thing there are two really really important global scale issues involving the atmosphere one of them is ozone depletion the other is global warming and the media have done an incredible job of getting the public completely mixed up about where one begins and the other ends they are completely separate separate causes separate effects and consequently different ways of addressing them trying to solve them and our job in environmental science is to separate those ideas out for you and so that you can understand and compartmentalize the one and the other realize that they are completely separate but identify also The Limited number of connections between them because like everything else one problem influences another in one way or another now if you think carefully and analytically about that survey question number five you should be able to work your way to the correct answer the Antarctic ozone hole is part of the issue called ozone depletion right now what's that all about high high in the atmosphere is a region called the ozone layer and the ozone layer is important to humanity because it protects us from what don't say the Sun or the sun's rays will need to be specific it protects us from the sun's ultraviolet rays the sun sends us Heat light and ultravart the ozone layer doesn't do anything for heat doesn't do anything for light protects us from ultraviolet what does ultraviolet do it causes sunburns skin cancers damage to living tissue living organisms Okay so what do we have here melting the ice cap temperature Heat nothing to do with ultraviolet letting in excess heat from the Sun heat temperature nothing to do with ultraviolet skin cancer yep that's it so what's going on in the ozone layer up in the stratosphere ultraviolet radiation coming from the Sun it's oxygen molecules regular o2s and splits them into single oxygen atoms now a single oxygen atom by itself is very very reactive and the first thing it does is look for something to bond to it bonds onto an O2 turning the twosome into a threesome which is ozone continued ultraviolet coming from the Sun breaks oxygen atom off of an O3 turning it back into an O2 and leaving one oxygen to find another O2 to combine with to form O3 so there's a continuous making and breaking and making and breaking process for ozone going on in the stratosphere specifically in what we call the ozone layer that process making and breaking ozone molecules absorbs uses up 95 of the incoming ultraviolet rays from the Sun now back on your survey environmental knowledge let's go straight on to the next question here because it's related um question number six you can help to protect the ozone layer by bicycling instead of driving not using oil-based paint having your old air conditioner professionally disposed of almost all of you picked bicycling instead of driving once again you're all wrong I'm sure you'll you'll learn somewhere in school about the principal substance what is it the substance that we are putting into the atmosphere that is causing this ozone depletion problem it's called freon what is freon it's the stuff used to make refrigerators and air conditioners function it's not a waste product from combustion it doesn't come from burning gasoline or diesel or any other fuel it's not a waste product going into the air as fumes escaping from any kind of combustion process it's a chemical specifically manufactured in a chemical Factory to be used in Refrigeration air conditioning and some other Industries so guess what right answer to this question is having your old air conditioner professionally disposed of so that when it reaches the end of its life the freon within within it does not Escape into the atmosphere so we clearly need to talk about ozone and very important to this is understanding why we have want use freon Refrigeration so let's start on refrigeration the refrigerator and an air conditioner basically do the same thing they cool down the inside of a box refrigerator cools the inside of a smallish box that you keep food in an air conditioner cools down the inside of a larger box that we live in how do we cool something down heating something is easy you expand energy turns into heat you heats up something but cooling is the opposite cooling is not adding energy cooling is removing energy how do you remove energy from something well there's only one really good way it's a very important principle in physics it's called evaporation when liquid evaporates into a gas the process requires energy takes it energy if you want to evaporate water give it energy if you're a wet surface evaporates much faster if the sunlight is hitting it adding energy then if it's in the shade if you want to evaporate water really fast you put it in a pan on the stove and eat it the more you eat it the more energy you put into it the faster it evaporates there are two ways of making your liquid evaporate one is by raising the temperature the other is by lowering the pressure that by the way is why there's no liquid water on Mars they don't have enough atmosphere the pressure is lower and so any liquid water immediately evaporates but if we can persuade a liquid to evaporate by lowering the pressure it still needs to get that extra from which therefore cooldown we've been using this process for cooling for years and years and years have you ever heard of a device called a swamp cooler ancient invention you blow the air into your home through the hanging curtain that you have totally moist as the air passes by it evaporates water and that evaporation cools the air down the air is cooler as it comes into your home that was what people did before they invented air conditioning it is if you like a primitive form of our condition and much cheaper here's a modern unit installed on the roof of a home in Arizona keeping the inside of the home at least 15 degrees cooler than the outside this process in a river we pump a liquid in an arrow pipe up to the top of the refrigerator this pipe in the ice box of the fruit refrigerator divides into many tubes kind of like so and I think you've seen in your traditional smaller refrigerator uh the metal of the ice box you can see this pattern of pipes within it right now the volume of the one pipe here is pretty small the volume of the many pipes is much greater and so as the liquid goes into this region here it expands in volume and therefore lowers in pressure and consequently evaporation takes place and that evaporation works by taking in heat taking heat away from the surroundings those pipes then rejoin and go back down to the bottom of the refrigerator as a larger tube so this contains gas moving in this direction this one had liquid moving off at the bottom here that goes into the compressor which repressurizes the gas that causes it to condense physics is reversible it condenses back into liquid and the liquid in the small pipe goes back up to do it again and the Heat comes back up down here this is the bottom of the refrigerator at little fam blows that heat out through the grill at the bottom into your okay cycle liquid evaporates into gas taking in heat the gas up condenses with condensation back into a liquid gives out the Heat takes in the heat gives out the heat takes in heat gives out Heat evaporates condenses evaporates condenses liquid gas liquid gas continuous process what we need for this to work is a substance which can convert from liquid to gas and back to liquid by the use of suitable pressure at around the temperature that we want to keep our food or whatever so water isn't much use to us to get water evaporating effectively we need higher temperatures or very very low pressures if the pressure is wildly different from the pressure of the atmosphere it means that you need better seals heavier stronger equipment all stuff that makes for inconvenience and expense back in the 19th early 20th century the substance that we used for this process was ammonia you know what pneumonia is right it's you fire you Buys in the cleaning aisle in your supermarket and oh it smells bad that isn't ammonia that's water with a tiny quantity of ammonia dissolved in it ammonia pure ammonia is at room temperature a gas and it doesn't just smell bad it is it'll kill you but uh high enough pressure it can be condensed into a liquid and when you lower the pressure it will evaporate can be used as a refrigerant does this sound like something that you want in your kitchen at home now heavy steel equipment powerful pumps because you're working at high pressure any kind of leak highly toxic could easily kill you no we don't want that in our homes so back in those days there was no such thing as a domestic refrigerator Inner City usually of course in the poorer neighborhood of the city there would be a giant industrial sized Refrigeration plant usually called the ice plant and it made blocks of ice then you had a delivery system carts horse-drawn hand pushed would deliver blocks of ice all around the city and what people had in their homes kind of looked like the freezer fridge combo of today but that upper box was simply an empty box you purchased a block of ice you put it in there you shut the door and the ice gradually melting over a week or so would keep the lower box below it the food it's called an icebox and it's what you used in your Victorian City Kitchen why sitting worked fine this delivery distance from the ice plant what if you lived out in the country on a farm far from a city with an ice Cloud well no ice a partial solution to that in parts of the country where Winter got cold enough people built ice houses they would dig a hole in the ground roof it over cover that roof with plenty of dirt for insulation and in the winter they would saw the ice off of Frozen ponds into blocks take it down there and fill the ice house with that ice and with any luck that would last if it was well enough insulated well on into the summer they could go get blocks of ice from the from their ice house and use those in their ice box to keep cool in the kitchen but if you lived in a warmer place where there wasn't a frozen winter or you didn't have an ice house no such thing as Refrigeration it was a different world people didn't store leftovers they didn't keep perishable items you made food you ate it and eat it you threw on a farm you fed it to your apples