Particulate matter in the air also affects climate change. Some types of particles reflect light and heat energy - or radiation - from the sun and therefore have a cooling effect in the atmosphere. Other particulate species absorb and re-emit radiation which causes a net warming effect. Particulates in the atmosphere also affect the formation of clouds which indirectly affects the amount of radiation entering and escaping from the troposphere.
Components of particulate matter that have a cooling effect (negative radiative forcing):
- Sulphates formed from the emissions of sulphur dioxide SO2, from fossil fuel combustion
- Nitrates formed by nitrogen oxides emitted by fossil fuel burning
- Ammonia (NH3) from agricultural sources promotes the formation of nitrates and sulphates
Components of particulate matter that have a warming effect (positive radiative forcing):
- Black carbon (soot) absorbs heat from the sun