Which greenhouse gas has maximum average residence time in the atmosphere?

Atmospheric residence time refers to the average duration a gas molecule remains in the atmosphere before being removed by natural processes. Among the options provided, Carbon Dioxide (CO2) has the maximum average residence time. While methane (CH4) lasts approximately 12 years [1] and nitrous oxide (N2O) lasts about 114 to 121 years [2], CO2 does not have a single lifetime value because it cycles between the atmosphere, ocean, and land. However, it is widely recognized that CO2 remains in the atmosphere for centuries, with about 20% remaining even after 1,000 years. In contrast, water vapour has a very short residence time of approximately nine days to one week. Therefore, CO2 is the most persistent of the listed gases, significantly impacting long-term global warming trends.

Sources

1. [1] Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 17: Climate Change > 17.5. GLOBAL WARMING POTENTIAL > p. 260
2. [2] Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 19: Ozone Depletion > Lifetime & removal of CFCs > p. 268