When NASA launched the Nimbus-4 satellite 50 years ago, nobody knew the ozone layer over Antarctica was thinning. And nobody knew that chlorofluorocarbons (CFCs)—long-lived chemicals that had been used in refrigerators and aerosol sprays since the 1930s—were responsible.
But the mission included a sensor called the Backscatter Ultraviolet (BUV) experiment capable of measuring ozone nonetheless. “We simply wanted to measure the atmosphere. It was curiosity-driven research,” said Pawan Bhartia, an atmospheric scientist at NASA’s Goddard Space Flight Center in an interview about the discovery of the ozone hole.
Developed by a team led by NASA’s Donald Heath, BUV was the first space-based instrument to measure the total amount of ozone in the Earth’s atmosphere. “Don was really sweating the Nimbus-4 launch because his MUSE instrument on one of the previous Nimbus satellites ended up in the Pacific Ocean offshore from Vandenberg Air Force Base,” said Arlin Krueger, technical officer for the BUV science team. “That instrument was recovered from the ocean floor and sat on his filing cabinet for years as a reminder that risks are big part of the NASA experimenter’s life.”
Fortunately, the launch went smoothly. The BUV performed well and demonstrated a new way to measure total column ozone. This led to the Total Ozone Mapping Spectrometer (TOMS) on Nimbus-7. The ozone data it collected gave researchers baseline measurements that, in the mid-1980s, helped them recognize that a troubling hole in the ozone layer had opened up.
The global recognition of the destructive potential of CFCs soon led to the 1987 Montreal Protocol, a treaty phasing out the production of ozone-depleting chemicals. Since then, scientists have begun to see definitive proof of ozone recovery.
You can find the latest data and imagery of the status of the ozone hole on NASA’s Ozone Watch website. You can read more about the role that satellites played in the discovery of stratospheric ozone depletion here.