Explanation:

Scientists for the first time have detected ammonia in the upper troposphere, the lowest atmospheric layer of Earth. The ammonia (NH3) was released into the atmosphere as agricultural emission from livestock farming and fertilisation. It is not washed out completely when air ascends in monsoon circulation. It enters the upper troposphere from the boundary layer close to the ground, where the gas occurs at relatively high concentrations. The detected ammonia may be playing a role in formation of aerosol (tiny particles made from super-fine solid particles) in the troposphere. The aerosol may have influence cloud formation and altering properties of existing clouds It is thought that accumulation of ammonia in the troposphere could have a cooling effect.
Hence, answer is C.