Lab Notes: What we can learn from the world's cleanest air
Belinda Smith: often hear about places with bad air quality, both here and overseas.
News Grab: Toxic particulates in Delhi's air measured over 700 micrograms on a scale where an annual average above 5 is deemed unsafe.
Belinda Smith: But what about where the air is, well, not just clean, but cleaner than anywhere else on earth? Well, it turns out that air can be found blowing onto the north-west tip of Tassie at a place called Kennaook/Cape Grim. There, you'll find an air pollution station, which, along with a bunch of similar facilities around the world, has quietly been keeping track of how we humans have been changing the make up of our atmosphere. And it's been doing this for nearly 50 years. So what can we learn from the world's cleanest air? Hi, I'm Belinda Smith, and you're listening to Lab Notes, the show that dissects the science behind new discoveries and current events. To explain what's going on at Kennaook/Cape Grim, is Ruhi Humphries, an atmospheric scientist at the CSIRO. So why is it important to collect this data?
Ruhi Humphries: You could very easily ask, it's super clean, why do we care? But if you're going on a diet, you need to know your before weight, so you can figure out your after weight and how much you've lost. And for climate change, if we want to understand our impact, and thus how to mitigate that effectively, we need to know what the atmosphere looks like without that pollution.
Belinda Smith: This station's been measuring the air for nearly 50 years now. What's so important about all that historical data?
Ruhi Humphries: Ideally, we'd build a time machine and we'd go back to the early 1800s, before the Industrial Revolution, and measure the atmosphere there. And we can kind of do that with ice cores, with some components, but with many components we can't do that. And so we have to find a location on the planet which is as clean as possible, without human influence as possible, so that we can really define that pristine baseline really well, so then we can understand what the impact of humans is, and thus how to mitigate for it.
Belinda Smith: That pristine baseline is measured in a place that cops winds straight off the Southern Ocean. And being there, unsurprisingly, it's...
Ruhi Humphries: remote and windy. I was looking at the data this morning, actually, and the wind speeds for the last 24 hours have been a minimum of 60km an hour. Oh, wow. Just
Belinda Smith: a breeze, really. Yeah,
Ruhi Humphries: yeah.
Belinda Smith: What does the air feel like when it goes into your lungs when you're standing there?
Ruhi Humphries: It gets pushed in, because it's so windy. But, yeah, it's just clean marine air. It's salty and doesn't smell like much, really, other than salt.
Belinda Smith: How do you know this air is the cleanest in the world? How do you measure that?
Ruhi Humphries: Same way you measure the dirty air, but you just have to have really sensitive instruments.
Belinda Smith: And Kennaook/Cape Grim gets a thing called the baseline sector from the southwest winds.
Ruhi Humphries: That's air that's come off the Southern Ocean and really hasn't touched land or had human influence for weeks, and a lot of the time has come off the Antarctic continent as well. So it's super clean, super pristine.
Belinda Smith: What sorts of things do you measure?
Ruhi Humphries: Your standard MET package, wind direction, temperature, that kind of stuff. But the main focus is really atmospheric composition, so what gases are there and what particles are there. So we've got greenhouse gas measurements, carbon dioxide, methane, nitrous oxide, that kind of stuff. We take flask measurements for CFCs and other long-lived fluorocarbons.
Belinda Smith: So they're things that can destroy ozone.
Ruhi Humphries: Exactly, yep. We do reactive gases like ozone, so ozone in the troposphere, so the part of the atmosphere where we live, rather than the stratosphere, which is where ozone's really good in the stratosphere, protects all life from UV. In the troposphere, it's a pollutant, and so you really need to measure it.
Belinda Smith: So 50 years ago, when Kennaook/Cape Grim, was identified as a primo posse to keep tabs on the atmosphere, an ex-NASA monitoring station, which was basically a very large caravan, was set up at the site to begin collecting data. Now there's a proper building and everything, so the facility has changed a bit. But more importantly, how has the air changed over that time?
Ruhi Humphries: There at Cape Grim, we've seen a 20% increase in a lot of the greenhouse gases around the world. The Southern Ocean is a really great place to measure that, because the Southern Hemisphere has about 10% land mass, I believe, and so you don't get that biosphere cycle that you get in the Northern Hemisphere.
Belinda Smith: Is that when plants use more carbon in the growing months and less in the wintry months? Correct,
Ruhi Humphries: yep. So you see this, basically, the biosphere breathe in and then breathe out and breathe in and breathe out with that seasonal cycle. So that's a lot less in the Southern Hemisphere, compared to the Northern Hemisphere, but you still see this really stark upward trend in all the greenhouse gases.
Belinda Smith: The Kennaook/ Cape Grim facility also picks up the signatures of big events that chuck a whole bunch of stuff into the atmosphere, like the 2020 bushfires.
Ruhi Humphries: They could be detected by monitoring stations all around the world. A lot of those fires actually went east from the east coast, and so in Cape Grim, we only would have seen them if they'd go right around the globe and then come back and then hit us at Cape Grim. When the wind was coming from the north, though, absolutely, we saw them, and we saw that smoke, and that's an active area of research that we use Kenilk, Cape Grim data for. Once those plumes, though, are above that surface layer, which happens quite quickly because they're so hot, we see them in different types of measurements. So instead of instruments where we've literally stuck a tube out the window and we're sucking air in at 10 metres above the ground, we actually have remote sensing instruments like they have on satellites where you've got an instrument on the ground looking up at the sun, and so anything in that path between that instrument and the sun, you can see.
Belinda Smith: I'm curious as to whether COVID made any difference to the measurements that you got at Cape Grim. Did that affect anything?
Ruhi Humphries: It's a big question that a lot of people around the world have tried to answer in terms of what impact COVID had on climate change. I think the short answer is it may have slowed it down for a moment, but not by much. Just for a moment. Just for a moment.
Belinda Smith: Yep. What about air quality?
Ruhi Humphries: Air quality was definitely improved. Air quality is a bit different, though, because it's a short-term phenomenon. So a lot of the stuff that impacts air quality will kind of â€' the lifetimes of those species in the atmosphere is quite short, and so once you remove the source, it doesn't take long for the air quality to drastically improve. So when you shut down a whole city, you get rid of all the cars and reduce your industry, your air quality will drastically improve.
Belinda Smith: Until everything starts up again. Until everything starts up again, exactly.
Ruhi Humphries: So the long-term solutions to air quality improvement are cleaner technology and getting rid of industries that â€' or cleaning up industries that are highly polluting.
Belinda Smith: Kennaook/Cape Grim also measures tiny particles that are suspended in the wind and the atmosphere? These are known as aerosols.
Ruhi Humphries: That could be sea salt or like sulfate aerosols or soot from cars or all sorts of things like that. And again, there's natural aerosols and then there's anthropogenic aerosols as well. But one of the really cool things that's happening at the moment at Cape Grim is we've got heaps of instruments to measure clouds and how the aerosols interact with clouds and really impact the properties of the clouds.
Belinda Smith: Properties such as how much sunlight and heat they reflect back into space.
Ruhi Humphries: You're in an aeroplane and you look down and there's clouds there and it's super reflective and you've got to put your sunnies on. If the clouds aren't there, you don't really need your sunnies. That reflection is really impacting how much light is getting to the surface, how much heat is getting to the surface, therefore what your climate is doing with that heat and how much of that heat can get trapped back into the atmosphere by the greenhouse gases. So
Belinda Smith: just getting back to aerosols, what do they have to do with clouds?
Ruhi Humphries: All clouds basically need an aerosol particle to form. So to form a cloud droplet, if you didn't have a little particle on which the water vapour can actually condense, then you'd need about 300% relative humidity to form a cloud. Right, okay, so it's like
Belinda Smith: dust or something? Yeah, so you've
Ruhi Humphries: got dust or sea salt aerosol or sulphate from cars or anything like that. So we call them cloud condensation nuclei. And so the number of those cloud condensation nuclei determines how many water droplets are in your cloud. And that determines your cloud lifetime and how reflective your cloud is. So in a polluted area, you might have lots and lots of aerosol particles. And so therefore your cloud droplets are much smaller for the given amount of water. You're dividing your amount of water into many particles and many droplets rather than just a few. Whereas in the clean atmosphere where there's not many aerosol particles, your cloud droplets therefore become bigger.
Belinda Smith: And so what does that do to the reflectivity of the cloud?
Ruhi Humphries: So the more droplets that you've got, the smaller they are, the more they reflect.
Belinda Smith: Oh, okay, all right. So the cloud cover here would be more reflective than the cloud cover over the Southern Ocean then? Yes,
Ruhi Humphries: except that the Southern Ocean is one of the cloudiest places in the world. Oh, okay. So you've almost always got cloud there as well.
Belinda Smith: Okay, so basically clouds are super complex.
Ruhi Humphries: One of the key things is that the Northern Hemisphere is much more polluted than the Southern Hemisphere. But the Northern Hemisphere is where 90% of the world's population live and that's where a lot more of the research happens. And so we understand that environment a lot more because there's been more studies there. Whereas in the Southern Ocean and Antarctica and our region, there's just less of that research happening, so we have less understanding of what's going on here.
Belinda Smith: Yeah, and what's going on here, you know, this whole half of the planet is pretty important when it comes to figuring out what to expect climate-wise.
Ruhi Humphries: It's probably one of the biggest uncertainties in climate models at the moment. And one of the things that really illustrates that to me is that there are so many international projects happening to try and answer this question. In the Southern Ocean and Antarctica, there's at least 25 in the last five years. There's a real focus from international agencies on trying to answer this question, like how are the clouds impacted by the aerosols and the biology that produces those aerosols.
Belinda Smith: Clouds are having their moment.
Ruhi Humphries: They are. They are. They're super important and super complex.
Belinda Smith: Adding to all this complexity are tiny organisms in the Southern Ocean called phytoplankton. They form the base of the marine food chain, but they also churn out stuff which can control the clouds above too.
Ruhi Humphries: So phytoplankton emit a range of different sulphur compounds and one of the really important ones that we've known about for a long time is dimethyl sulphide. And so these phytoplankton emit this in the ocean and then that then vents out into the atmosphere and then that undergoes chemistry to get to sulphur dioxide, which then goes to sulphuric acid, which then clumps together into aerosol particles and grows into sizes generally, which they can be cloud condensation nuclei.
Belinda Smith: And boom, there's your cloud.
Ruhi Humphries: So there's this theory that phytoplankton can control the clouds, right? And then there's this whole feedback mechanism, right? Because the clouds then shade the sun and the phytoplankton feed off the sunlight and so then they produce less. Oh, so it's self-regulating. Yes, exactly. So that's a theory that's been around for 40, 50 years and some level of truth to it, but it's way more complicated than they initially suggested.
Belinda Smith: Feels like anything to do with the climate is way more complicated than was initially thought.
Ruhi Humphries: I think so, yes.
Belinda Smith: That was Ruhi Humphries, an atmospheric scientist at the CSIRO. And thanks for listening to Lab Notes on ABC Radio National, where every week we dissect the science behind new discoveries and current events. I'm Belinda Smith. This episode was produced on the lands of the Wurundjeri and Menang Noongar people. Fiona Pepper's the producer and it was mixed by Roi Huberman. We'll catch you next week.
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