Which one of the following greenhouse gases is in largest concentration in the atmosphere?

Among the greenhouse gases listed, carbon dioxide (CO2) has the highest atmospheric concentration. As of early 2025, CO2 levels have reached approximately 426 parts per million (ppm). In comparison, methane (CH4) concentrations are significantly lower, measured at approximately 1.9 ppm (or 1900+ ppb) [2]. Nitrous oxide (N2O) exists in even smaller quantities, around 0.33 ppm (330+ ppb). Chlorofluorocarbons (CFCs) and other fluorinated gases are considered 'minor' greenhouse gases with concentrations typically measured in parts per trillion (ppt). While water vapor is the most abundant greenhouse gas overall, among the primary anthropogenic gases listed in the options, carbon dioxide is the most prevalent by volume. Its concentration has risen by over 150% since the Industrial Revolution due to fossil fuel combustion and land-use changes.

Sources

1. [2] https://www.epa.gov/ghgemissions/overview-greenhouse-gases