What Fukushima can teach us about coal pollution

Earlier this week, I told you about a new study tracking radioactive fallout from the nuclear power plant disaster in Fukushima, Japan.

It started with a team of researchers in California, who had been monitoring radioactive sulfur in the atmosphere since 2009. Last spring, after an earthquake and tsunami critically damaged several reactors at the Fukushima Daiichi power plant, those researchers watched the levels of radioactive sulfur skyrocket, relatively speaking. The amounts of radioactive sulfur that reached the California coast weren't high enough to be a threat to humans, but they made a big impact on extremely sensitive monitoring equipment.

Using that data, the researchers were able to figure out where the radioactive sulfur came from and back-calculate how much would have been produced at the site of the disaster—information that can tell us something about how dangerous the disaster really was to people living nearby.

But these researchers weren't the first to collect radioactive isotopes from Fukushima on American shores. And they weren't the first to offer up improved estimations of how much radiation leaked from the damaged power plant in the early days of the disaster. I thought this study was interesting. But, like a lot of you, I was left wondering why it was important.

Then yesterday, I interviewed Antra Priyadarshi, the lead author on the peer-reviewed paper that was published about this study. And I realized I'd gotten the story all wrong. This paper is about radioactive sulfur from the Fukushima disaster. But it isn't about the Fukushima disaster. It's not even about nuclear power. Not really.

In reality, this is a paper about coal. And it's important because of what it can tell us about the sort of air pollution that is much more mundane—and more deadly—than the fallout from a single nuclear disaster.

To get this, you first have to understand who the researchers are and why they've been monitoring radioactive sulfur for so long. It has nothing to do with nuclear power or nuclear weapons.

Antra Priyadarshi is a postdoc—a scientist who has recently earned their Ph.D., but is doing research under the guidance of another, older scientist. You can think of it like an apprenticeship program, in a way. Priyadarshi works in the lab of Mark Thiemens, an atmospheric scientist. The Thiemens Lab is interested in questions of climate systems and the chemical makeup of the atmosphere. In particular, they're interested in ozone.

Ozone is a molecule of three oxygen atoms bound together, and it's the same stuff that makes up the protective ozone layer around there Earth. Way off in the upper atmosphere, ozone is a Good Thing. But context matters. When ozone ends up on our level, where humans can breathe it in, it becomes a problem. That's because ozone can, essentially, give the lining of your lungs a sunburn. The more ozone you inhale, the more damage to your cardiovascular system.

There's a couple of reasons ozone and people come into contact. One is pollution: On hot days, chemicals from car and factory exhaust can turn into ground-level ozone. But ozone from the upper atmosphere can also get transported down to our level naturally. One of the key things the Thiemens Lab is trying to understand is how those natural movements work, why they happen, and what that means for the way pollution-based ozone gets transported from exhaust-rich urban areas to other parts of the world.

This is where the radioactive sulfur comes in, because there's a natural source of that, as well.

In the upper atmosphere, where the naturally occurring ozone is formed, high-energy particles from cosmic rays react with argon to form radioactive sulfur. When air from high altitudes intrudes on our atmospheric level, it brings both ozone and radioactive sulfur along for the ride. Antra Priyadarshi has been monitoring radioactive sulfur both because of the role those isotopes play in climate—there's some evidence that they can serve as points for clouds to condense around and produce raindrops—and because of what the movement of sulfur can tell her about the movement of ozone.

So that explains why Priyadarshi and her colleagues were out there monitoring radioactive sulfur to begin with. But why is this paper important? What does it add to her research?

For that, you have to look to China, and a different form of sulfur.

The Smell of Success

When we burn coal, one of the things that goes up in smoke is sulfur dioxide. It's not radioactive, but it is dangerous. Sulfur dioxide, like ozone, damages human respiratory and cardiovascular systems. It's a key ingredient in acid rain, which harms crops and other plants, and damages buildings. And it's also a major player in producing particulate matter—tiny grains that get inside your lungs and cause long-term damage.

Particulate matter is also an important factor in climate change. That's because, while particulates are very bad for human health, they also play a role in cooling down the planet. Basically, greenhouse gases in the atmosphere trap heat and particulate matter in the atmosphere prevents heat from the sun from getting in. These two forces work against each other, even though, in man-made terms, they come from the same place—fossil fuel emissions.

When we talk about cleaning up emissions, we're usually talking about reducing the amount of sulfur and particulates produced, but not the amount of greenhouse gases. So, ironically, cleaner tailpipes and smokestacks save lives in the short term, but contribute to a rising global temperature in the long term.

That's why people are watching China. Western countries started scrubbing sulfur out of their emissions decades ago. Our emissions aren't sulfur-free, but they're a lot cleaner than they used to be. China, on the other hand, is rapidly ramping up the amount of coal it burns, and the emissions aren't being cleaned up. It's the world's largest sulfur dioxide polluter today. And scientists are curious about how that sulfur dioxide in the atmosphere is masking the effects of greenhouse gases. When China starts cleaning up its smokestacks, what will happen to the global temperature? How does sulfur dioxide from China affect the rest of the world?

That second question has been very difficult to answer. Think of all the coal that gets burnt everywhere, every day. In order to know something about how sulfur dioxide travels, you have to be able to separate the sulfur dioxide from one factory, or one power plant, and trace it as it moves through the atmosphere. That's like listening to five symphonies playing at once and trying to pick out the work of a single flautist.

Until now.

This is why a study of radioactive sulfur from Fukushima matters. That disaster produced so much radioactive sulfur that it was obvious when the plume from Fukushima reached the shores of California. This signal was loud enough to stand out from the noise. The radioactive sulfur from Fukushima isn't exactly the same thing as the sulfur dioxide from Chinese power plants, but it is close enough that it can serve as a marker. It's a model that can tell scientists some important things about how sulfur travels through the atmosphere and how it crosses great distances, like the Pacific Ocean.

"There are lots of sources of sulfur pollution and a lot of uncertainty in the models," Antra Priyadarshi said. "But this is a case when we can know better how much radioactive sulfur was produced at the source, and how much arrived, and you can neglect the natural background signal. That gives you a better estimation of how much sulfur could be transported over the Pacific."

Photo by Dawn Erb. Used with permission.