Which statement best describes the source of atmospheric chlorine?

Which statement best describes the source of atmospheric chlorine?

• A. Natural sea spray only
• B. Chlorine is not present in the atmosphere
• C. Human-made chemicals such as CFCs are a major source
• D. Chlorine comes from volcanic eruptions

Answer: (C)

Atmospheric chlorine mainly comes from human-made halogenated compounds such as chlorofluorocarbons. These substances are very stable in the lower atmosphere, and when they reach the upper atmosphere they break down under ultraviolet light to release chlorine atoms. Those chlorine atoms participate in catalytic cycles that destroy ozone, making anthropogenic emissions the dominant source of atmospheric chlorine. Natural sources like sea spray do contribute chlorine, but their input is much smaller in comparison to the long-lived, widespread emissions from CFCs and related chemicals. The other statements don’t fit because chlorine is present in the atmosphere, volcanic sources exist but are not the major contributor, and sea spray alone does not account for the majority of atmospheric chlorine.

Atmospheric chlorine mainly comes from human-made halogenated compounds such as chlorofluorocarbons. These substances are very stable in the lower atmosphere, and when they reach the upper atmosphere they break down under ultraviolet light to release chlorine atoms. Those chlorine atoms participate in catalytic cycles that destroy ozone, making anthropogenic emissions the dominant source of atmospheric chlorine. Natural sources like sea spray do contribute chlorine, but their input is much smaller in comparison to the long-lived, widespread emissions from CFCs and related chemicals. The other statements don’t fit because chlorine is present in the atmosphere, volcanic sources exist but are not the major contributor, and sea spray alone does not account for the majority of atmospheric chlorine.