The Ozone dectectives hunting ozone-killing chemicals
BBC: 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.
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.
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.
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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.