 Carbon dioxide is a gas, it's all around us, you can't see it, it's invisible and there's only a small amount of it in the air but it's really important because it absorbs heat and right now it's making the planet warmer because it's increasing. Carbon dioxide is a carbon in two oxygens so it's written as CO2, so I usually just say CO2 for short. It's invisible but we've had instruments that can measure its concentration for about 70 years and in the late 50s measurements were started at a place called Manaloa in Hawaii, on the big island of Hawaii, so what I'm going to do is draw a graph, the numbers on the left are showing the concentration of CO2 in parts per million of CO2, so I'll write a big PPM CO2 over here and then on the this axis over here is just the time or the date so these are years. When those measurements were started in the late 50s the concentration of CO2 in the atmosphere was around 350, 318 parts per million so it was about right there and Dave Keely and the person who started these measurements found out after about a couple years that they were going up but they weren't going up in a straight line, they were kind of wiggling so CO2 has been doing something like that ever since and it started going up even faster and by the time it got to around 2000 it was in sort of the 38390 range and then it crossed 400 right about 2016 and now we're right about 415 parts per million for the global average. The reason that CO2 concentration is going up is because we're burning all these fossil fuels in our cars and power plants so those are fuels that were buried underground for millions of years. We've been measuring carbon dioxide continuously at a place outside of Netherlands, Colorado called Nyawa Ridge so this is at about 11,000 feet altitude. We actually started those measurements in 2005 and if I plot those on here they are a lot noisier than the red curve and what they actually do is they go lower during the summer and they go higher during the winter and lower during the summer and higher during the winter. We became interested to see what it was even closer to home so we installed an instrument here at the Mesa Lab and that's been going since 2012 and what we found then was that CO2 was even more variable and it went from about the same place as the others but it went all the way up to 650 parts per million. Every you know every few days there's a spike that goes way up and the reason it's more variable could be because there are people walking around the building but it could also be because there are more cars and until recently a coal burning power plant here in Boulder and other sources of CO2 around the around the front range. So one thing we've noticed is that in the middle of the morning there is often a spike in CO2 here at the Mesa Lab and we've kind of wondered if that was because people were showing up to work late or driving around Boulder or if it's because the way the air mixes it just brings all the CO2 from down in Boulder to us. So we're gonna try and do some vertical profiles by biking up and down the hill with the CO2 analyzer to during the morning transition period to get a better idea of what's causing CO2 at the Mesa Lab to vary. Okay let's go get Tim to bike this CO2 analyzer up and down the hill a bunch of times. So this is the bike CO2 analyzer. Check that out. Yeah it's like other instruments that we have at field stations or on airplanes but it's smaller and battery powered. So it's like a big lunchbox. Yeah there's I don't think you want to eat what's in here. And there's a little pump and I think I can turn it on here. You can hear the pump running and that sucks air in to the instrument from a tube that is out on the front of the bike. And then the actual instrument I can take the lid off and we can look inside. It's a little bit easier to tell what's going on. If you can see in here there's two tubes one going in and one coming out so that the pump's gonna suck the air in from outside and push it through these tubes. And on one end of this gold colored cylinder that's the word I'm looking for is a lamp. So it's a little tiny almost like a light bulb that produces infrared radiation. On the other side is a detector that can sense how much is there. So if there's more CO2 in between here that would be less infrared radiation making it to the other end. So there's a signal we measure the voltage and the voltage we go down when the CO2 goes up. But we basically just turn this on and turn the pump on and it'll measure continuously the whole time you're going. We get a number every second and it also measures pressure at the same time. And that's how we're going to tell how high you are on the road because sea level pressure is around 100 kilopascals or 14.7 pounds per square inch. Up here it's about 80% of that because we're 5,000 feet above sea level so there's a lot less air above us. And there's actually a lot less air above us here at the NCARF Mesa lab than there is down at the intersection of Broadway and Table Mesa. And the skies are pretty blue. Yeah. And there you go. We're all set. Just like that. There you are. Thank you. 80.6 kilopascals. So as they start going down that number will start going up. At some point on the way down that hill CO2 went way up. Maybe we should call Tim and find out where he is. Hello. Hey Tim. Hey. Where are you? You hit about 475 ppm and it was a pretty sharp transition. Right about where you are now it looks like. Oh really? Clearer? It's definitely colder here. We're getting the occasional uptick. I don't know. Maybe let's learn by. Okay. Interesting. It went up to like 500. 500. Car CO2. Car CO2. A little bit noisier on the way up because those are the cars that went by and maybe a little bit of your breath but you can see the kind of a baseline. I don't know this time if you go down there if it's going to go higher concentration of CO2 because there are more cars. People are commuting to work or if it's going to go lower because the sun's up and it's heated the ground and caused more mixing to happen. So we don't know. Yeah. Let's do it again. I'm getting ready to come back up. Okay. We're actually on table mason now and a couple of cars are going by. Oh that's not you right there is it? You're at 419 now. There was you were 440 for about two minutes on the way up there so I don't think that was a truck. I think that was just a puff of dirty boulder air. You can see it's so peaceful out here. And EV just went by full electric. That was a gas burning car and the electric car didn't do anything. But you know if you ignore the spikes from the cars the CO2 has been going down slowly as you've been climbing up. Bike number two was a success and I managed to convince Tim and Riva to do it one more time. CO2. I'm so curious what it's gonna look like this time coming back up. Which is what it is up here. So it's like this this slug of dirty air is moving up in like a layer. Oh. Tim and Riva biked up and down the hill three times and now we're gonna check out what we measured. What I'm showing here is a graph of carbon dioxide concentration as a profile a vertical profile on the hill. Pressure goes up as you go down and so the y-axis is a pressure and it's reversed so lower values are up and higher values are down. So that that makes it a line with the real world. So you can kind of think of this graph as representing the NCAR Mesa lab at the top left and then the intersection of Broadway and Table Mesa at the bottom right and then the x-axis is the carbon dioxide concentration. So concentration was almost constant most of the way down the hill and then all of a sudden right as they got near the bottom it went shooting way up. So that's really cool. I think this is a result of all of the pollution that builds up overnight in Boulder. The air is usually pretty calm. All of the burning of gas in cars and burning of natural gas to heat homes produces CO2 that accumulates overnight. So let's see what we got when we compare all the profiles we did. That's shown on this graph. So again this is pressure on the y-axis and carbon dioxide on the x-axis and the Mesa lab is at the top left and the Broadway Table Mesa intersection is at the bottom right. This is really cool. So we didn't measure the same thing every time. It changed a lot but I think it changed in ways that that we can understand. So the the very first time down and up are the red and the orange line and they went they went way up to about 460 parts per million and on the way back up the orange line we saw some looks like little plumes of high CO2 on the way back up. The very next time that Tim and Riva went down were the green lines here and carbon dioxide was actually higher kind of on the hill on the way down but then when they got to the bottom of the hill it didn't the concentration didn't go up as much. I think what that is is the air is starting to mix so it's the Sun is coming up and it's heating the surface and it's making that air warmer and the warmer air wants to rise and so sort of slowly coming up the hill and then they did it one more time they were having so much fun they wanted to go again at around 1030 and those are the blue lines and those are crazy. They they they saw really high CO2 concentrations on the way down the hill and then when they got to the bottom the concentration was actually even lower than before. So I think that they just happened to catch this big plume of dirty boulder air that was kind of wafting up the hill in the mid morning and that happens to be exactly the same time when we saw some big spikes in the CO2 concentration in our measurements here at the Mesa lab and it's the same time when we usually see them so I think it's pretty clear that the spikes we see up here in the mid morning are a result of all this air that's accumulated overnight down low getting sort of sucked up past the past the Mesa lab. So now we know why we get these big spikes of CO2 up here at the Mesa lab in sort of the mid to late morning and that's great if we could only convince Tim and Riva to bike up and down the hill three or four times every day we could really do a great research project.