In the standard exam classification, which of the following greenhouse gases…

CONCEPT

Greenhouse gases absorb and re-emit outgoing infrared radiation. Their atmospheric origins can be natural, human-made, or a combination of both.

APPLICATION

Classify each listed gas by the processes that place it in the atmosphere:

• Carbon dioxide is released by respiration, decomposition, ocean exchange, and volcanic activity.

• Methane is released by wetlands, termites, ruminant digestion, and geological seeps.

• Nitrous oxide is released by microbial nitrification and denitrification in soils and oceans.

• In this exam classification, halocarbons denotes the synthetic subgroup, such as chlorofluorocarbons used in refrigeration and other industrial applications.

CROSS-CHECK / CONTRAST

Carbon dioxide, methane, and nitrous oxide each have documented natural emission pathways. The EPA distinguishes synthetic halocarbons as emitted exclusively from human activities. Some halocarbons, such as naturally produced methyl halides, do occur in nature, so the exam answer relies on the intended synthetic-halocarbon usage.

RESULT

Under the official exam convention, Halocarbons is the accepted answer.