What is the primary source of chlorine in the stratosphere?

What is the primary source of chlorine in the stratosphere?

• A. Volcanic emissions
• B. Ocean chlorination
• C. Natural atmospheric chlorine only
• D. Emissions of refrigerants by humans like CFC and HCFC

Answer: (D)

Chlorine in the stratosphere mainly comes from human-made refrigerants and related halogenated compounds, such as CFCs and HCFCs. These molecules are very stable in the lower atmosphere and can travel up into the stratosphere intact. There, ultraviolet light breaks them apart and releases chlorine atoms. Those chlorine atoms participate in catalytic cycles that destroy ozone—each chlorine atom can destroy many ozone molecules before it’s removed from the cycle. Because the industrial production of CFCs and HCFCs has released huge amounts of these compounds, they are the dominant source of stratospheric chlorine. Volcanic emissions and oceanic processes do contribute chlorine, but their total impact on the stratosphere is much smaller compared with the vast reservoir of chlorine released from anthropogenic halocarbons. Natural chlorine exists, but it does not account for the level of stratospheric chlorine observed, making human-emitted refrigerants the primary source.

Chlorine in the stratosphere mainly comes from human-made refrigerants and related halogenated compounds, such as CFCs and HCFCs. These molecules are very stable in the lower atmosphere and can travel up into the stratosphere intact. There, ultraviolet light breaks them apart and releases chlorine atoms. Those chlorine atoms participate in catalytic cycles that destroy ozone—each chlorine atom can destroy many ozone molecules before it’s removed from the cycle. Because the industrial production of CFCs and HCFCs has released huge amounts of these compounds, they are the dominant source of stratospheric chlorine.

Volcanic emissions and oceanic processes do contribute chlorine, but their total impact on the stratosphere is much smaller compared with the vast reservoir of chlorine released from anthropogenic halocarbons. Natural chlorine exists, but it does not account for the level of stratospheric chlorine observed, making human-emitted refrigerants the primary source.