The Montreal Protocol limited the world’s use of chemicals like Chlorofluorocarbons (CFCs). Which sentence best indicates that the Montreal Protocol led to improvements in the thickness of the ozone layer? When ozone was first measured by satellite in 1979, the average concentration above Antarctica was 225 Dobson units (DU). In 1989, when the Montreal Protocol took effect, it was 127 DU. The lowest level was 92 DU in 1994.By 2019, the value was back up to 167 DU. Excerpt courtesy of NASA