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The detectives hunting ozone-killing chemicals

It was a research station on the side of a volcano, 4,000 metres above sea level, that picked up the key signal: despite an international ban, someone, somewhere, was emitting an ozone-damaging pollutant.


Stephen Montzka of the US’s National Oceanic and Atmospheric Administration (NOAA) was the first to notice. He had been analysing data collected at various sites since 2013. The measurements suggested that the decline of a dangerous chemical in the atmosphere, CFC-11, had been unexpectedly slowing down. “The finding was so surprising I had to be sure it was real,” he recalls.

美国国家海洋和大气管理局(NOAA)的蒙扎克(Stephen Montzka)是第一个注意到此状况的。自2013年以来,他一直在分析于不同地点收集的空气数据。测量结果表明,大气中危险化学品氟利昂(CFC11, 多年前被广泛运用于制冷剂和发泡剂,因对臭氧产生破坏而被禁用)的消退速度减缓了,这与科学家的预期不相符合。"这一发现令人感到惊讶,我决定要进一步确认。"他回忆时说道。

But it was the Mauna Loa data that convinced him. Since the 1950s, the Mauna Loa Observatory on the giant Hawaiian volcano of the same name has continuously monitored air as it wafts across the Pacific Ocean. In May 2018, an article published in the journal Nature revealed the worrying discovery in detail – CFC-11 was blowing over the Pacific Ocean from East Asia.

而莫纳罗亚天文台(Mauna Loa)的数据证实了他的猜想。自20世纪50年代以来,巨型夏威夷火山上的莫纳罗亚天文台不断监测着从太平洋飘过的空气数据。2018年5月,发表在《自然》杂志上的一篇文章详细揭示了令人担忧的发现——飘过太平洋的氟利昂来自于东亚。

Now, an international investigation is underway to find the source. That process could never have started without those initial measurements. By ‘sniffing the air’ and monitoring the levels of various gases in it, scientists are able to detect the presence of pollutants. This is the story of how they do it – and what happens when they find something fishy.


Chlorofluorocarbons, or CFCs, were banned internationally in 1996 under an important treaty called the Montreal Protocol. Through the treaty, countries around the world decided how they would protect ozone – a trace gas in the atmosphere that keeps out ultraviolet radiation emitted by the sun. CFCs contain the ozone-destroying gas chlorine, which is gradually released from the CFCs as they linger in the atmosphere. Stopping CFCs from being used in products and by industry was meant to result in their steadily accelerating decline.


But Montzka and colleagues noticed that, since 2012, the rate of decline for a particular CFC, trichlorofluoromethane – CFC number 11 – had gone off track.


There were various bits of evidence that pointed to a potential new source of CFC-11, says co-author Alistair Manning at the UK Met Office. This included the fact that the gradient, or difference in levels of atmospheric CFC-11 in the northern hemisphere and southern hemisphere, was diverging.

英国气象局的曼宁(Alistair Manning)表示,有各种各样的证据表明,氟利昂可能的新来源为东亚。这包括北半球和南半球大气氟利昂数据呈现出明显的梯度或差异。

“That narrowing of the gradient – it was starting to widen again, which then pointed to the fact that maybe there are new emissions in the northern hemisphere,” he says.


But that wasn’t enough to prove that someone was emitting a lot more CFC-11. It took the Mauna Loa data to reveal that. Manning was able to use the Met Office’s atmospheric dispersal-modelling tool to confirm the likely place from which this potential new CFC-11 had originated. He discovered that whenever Montzka’s CFC-11 measurements at Mauna Loa were lower, there was less wind from the direction of East Asia.


“That’s another part of the jigsaw – something happening in East Asia that could possibly be causing this increase in emissions,” says Manning.


When news broke that the prohibited gas appeared to be leeching out of East Asia, many were keen to look more closely. The UN, for one, has launched an investigation. But the paper in Nature also caught the attention of the Environmental Investigation Agency (EIA), a charity that campaigns against environmental crime and abuse.

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“As soon as we read it… we realised it was a really big deal,” says Clare Perry, a campaigner at the agency.

"我们一读到它......就意识到这是一个非常重要的事情",该机构的活动家佩里(Clare Perry)说道。

She and her team immediately thought to look for potential sources of CFC-11 in China. Researchers contacted several Chinese companies that process chemicals or make products that could be insulated with foam containing bubbles of CFC-11. The responses were candid. A representative at one firm allegedly said, “We purchase CFC-11 and mix it up. You see, nobody comes to inspect our processing work.”

佩里和她的团队立即开始在中国寻找氟利昂的来源。研究人员联系了几家中国公司,它们都调配过化学品或是直接生产隔热用的泡沫材料, 这种材料中含有氟利昂。中国公司的答复很坦诚。一家公司的代表说:"我们购买氟利昂并混合使用。事实上,没有人会来检查我们的加工工作。"

In all, the EIA says it received indications from 18 companies that they use CFC-11 in some form, often when blowing insulating foam into appliances and buildings.


The challenge now is to prove that such activity can account for the additional volume of CFC-11 apparently being released every year: about 13 million kilograms, according to Montzka and his colleagues.


“Sniffing the air” sounds simple, but the science involved in actually measuring molecules or particles in the atmosphere is a little more complex. The method used to detect the CFC-11 at Mauna Loa was gas chromatography, a process by which gases in a sample of air are separated along a long, coiled tube. As they’re blown along the tube, the rate at which they arrive at the other end is measured and compared. Larger particles, for instance, arrive more slowly than smaller ones. Mass spectrometry, the science of identifying molecules by their mass, is often used in conjunction with chromatography.

"嗅探空气"听起来很简单,但实际测量大气中分子或粒子的科学原理是十分复杂的。用于检测莫纳罗亚天文台中氟利昂的方法是气相色谱法(gas chromatography),这种方法将空气样本中的气体沿着长的盘管分离。当它们沿着管子飘动时,测量并比较它们到达另一端的速率。较大的颗粒比小的颗粒更慢地到达。质谱法是通过质量鉴定分子,通常与色谱法结合使用。

And then there’s the instrumentation needed to measure particulate, tiny clumps of solids or liquids that float around in the air.


This can be done by shining light through, say, a column of smoke and measuring how the light is scattered sideways off the particles. Tools that do this sort of measuring were unexpectedly put to the test this year, when a large wildfire broke out on Saddleworth Moor in the north of England in June. The fact that something was burning was no mystery – in fact, the fire was so large that a plume of smoke from it was easily visible from space.

通过将光线穿过一列烟雾,测量光线如何从粒子侧面散射,可完成这项任务。这种测量工具今年意外地得到了实际运用。在今年6月份,英格兰北部的萨德尔沃思沼泽(Saddleworth Moor)发生了一场大型野火,火势之大,从太空中都可以看到一股烟雾。

But how polluting was the fire? That’s something not discernible with the naked eye. To find out, a new array of instruments for measuring air quality at the University of Manchester were used. They revealed an extremely high concentration of particulate, which is highly polluting. The particulate comes from organic matter, vegetation, as it burns and smoulders. In fact, the lingering smouldering stage of a wildfire is when vast amounts of particulate matter are released.


As with CFCs, part of the objective in keeping an eye on the atmosphere is to see whether countries are accurately reporting how much of a certain pollutant they have emitted in a given period. These declarations are often required as part of environmental protection regulations.


Sometimes, this kind of double-checking yields good news.


Earlier this year, a paper reported that California appears to be accurately cataloguing its fossil fuel carbon dioxide (CO2) emissions. To check, co-author Heather Graven of Imperial College, London and her team used accelerator mass spectrometry to measure the ratio of different kinds of carbon in atmospheric CO2. Carbon-14 is a new, slightly radioactive carbon that is produced naturally in the atmosphere. Fossil fuel carbon has been around for many millions of years and has consequently decayed to become carbon-12, which has a slightly smaller mass and is no longer radioactive. Therefore, a lower ratio of carbon-14 to carbon-12 in the atmosphere is an indication that fossil fuel CO2 emissions are up.

今年早些时候,一篇论文认为,加利福尼亚似乎准确地报告了化石燃料二氧化碳(CO2)的排放量。为了核查,伦敦帝国理工学院的格雷文(Heather Graven)和她的团队使用加速器质谱法测量大气二氧化碳中不同种类碳的比例。碳14是一种新的轻微放射性碳,在大气中自然产生。化石燃料碳已存在数百万年,并因此腐烂成为碳12,其质量略小且不再具有放射性。因此,大气中碳14与碳12的比率较低表明化石燃料的二氧化碳排放量增加。

“From the data that we have, and incorporating atmospheric models, we found what we observed is very similar to what we expected,” says Graven.


“The atmospheric data is providing a tentative validation of what California is reporting.”


What floats around in the air doesn’t just tell us about fossil fuel pollution or the release of banned chemicals – it can also reveal unreported activity with nuclear weapons and radioactive materials used in the nuclear energy industry.


There is a worldwide radionuclide monitoring network that takes constant samples of the air in an effort to pick up unexpected radioactivity. After an above-ground nuclear accident or explosion, radioactive isotopes, or radionuclides, are released into the atmosphere and blown around by the wind. Stations all over the globe sample the air once a day and radiation detectors can tell exactly which isotopes are present.


In October 2017, the French radiation safety authority (IRSN) disclosed that a strange, small spike in ruthernium-106 had been detected by several European networks.


The IRSN was quick to determine that the levels wouldn’t be harmful to human health, but discovering this particular isotope was a worry, recalls Jean-Luc Lachaume at the IRSN.

法国核安全机构很快就确定,空气中如此浓度的钌106不会对人体健康产生危害,但发现这种特殊的同位素让人担忧,该机构的拉肖姆(Jean-Luc Lachaume)回忆道。

“This level of activity is totally unusual,” he says. “That radionuclide is an indicator of an incident or accident at a nuclear facility.”


We know this because specific kinds of nuclear activity cause specific radionuclide releases. For example, you might expect to see some iodine-131 in the atmosphere, says Lachaume, because it is associated with radioactive materials used in hospitals. Ruthenium-106 is much rarer.


Public information, including some found online, raised the suspicions of IRSN researchers that the source of the radionuclide was Mayak, an isotope plant in Russia, which had been due to produce cesium-144 in 2017. The industrial process for making that isotope would involve the creation of ruthenium-106. What’s more, analysis of wind patterns – much like the work done to investigate the source of CFC-11 – also suggested a place of origin in eastern Russia.


Did an accident at Mayak cause the unintended release of ruthenium-106 into the skies over Europe?


When quizzed about it, Russian officials said there was no safety incident at Mayak to report. Lachaume has been left not knowing exactly what to think, given the lack of conclusive evidence that Mayak definitely was the source.


“There are some mysteries in the universe,” says Lachaume, “and this is one of them.”


But with scientists around the world ‘sniffing the air’, some mysteries are becoming easier to solve. In the wake of nuclear accidents or illegal, unreported emissions, these people are often the first to know – the first to reveal an otherwise invisible truth.




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