Consider the following which can be found in the ambient atmosphere: Which of the above contributes to the warming up of the atmosphere?

Answer: (d) 1, 2 and 3

All three warm the atmosphere.

Statement by statement

1. ✓ YES Soot (black carbon) absorbs sunlight and darkens snow.

2. ✓ YES SF₆ is one of the most potent greenhouse gases (about 23,500 times CO₂ over 100 years).

3. ✓ YES Water vapour is the largest natural greenhouse gas.

The idea

Something in the air warms it in one of two ways. A greenhouse gas absorbs the infrared heat leaving the Earth (water vapour, sulphur hexafluoride). A dark particle absorbs sunlight directly (soot). Both end up heating the air.

Soot: dark particle → absorbs sunlight → heats the air around it → Sulphur hexafluoride: gas → absorbs infrared → lasts thousands of years → Water vapour: gas → absorbs infrared → the most abundant greenhouse gas

The trap

Soot is an aerosol, and some aerosols cool — but black carbon warms.

Also know

Sulphur hexafluoride is used as an insulator in electrical switchgear. Water vapour works as a feedback: warmer air holds more of it, which adds to the warming started by other gases. Not every particle warms: sulphate particles reflect sunlight and cool the Earth, as after the Pinatubo eruption of 1991.