Which observation is part of the evidence that CFCs and HCFCs are thinning the ozone layer?

Environmental impacts · EPA 608 Core. The correct answer, and the reasoning behind it.

How CFCs and HCFCs destroy stratospheric ozone, and what that does to health and the environment.

The question

Which observation is part of the evidence that CFCs and HCFCs are thinning the ozone layer?

• AChlorine levels in the stratosphere matching volcanic activity
• BSteady increases in ozone over the poles since the 1950s
• COzone levels rising wherever CFC sales went up
• DOzone loss over Antarctica alongside high chlorine levelsCorrect answer

Why “Ozone loss over Antarctica alongside high chlorine levels” is correct

Scientists have measured deep seasonal ozone losses over Antarctica, the so-called ozone hole, in the same stratospheric air where chlorine compounds from CFCs are high. That pairing of ozone loss with man-made chlorine is a key part of the evidence.

Source: EPA: Test Topics

Why the other answers are wrong

• Chlorine levels in the stratosphere matching volcanic activity — Stratospheric chlorine tracks CFC use, not volcanic activity.
• Steady increases in ozone over the poles since the 1950s — Polar ozone has fallen, not risen, since CFCs came into wide use.
• Ozone levels rising wherever CFC sales went up — Ozone falls, not rises, as chlorine from CFCs builds up.

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