What is Stratospheric Aerosol Intervention (SAI)

About Stratospheric Aerosol Intervention (SAI)

• Stratospheric Aerosol Intervention (SAI), also known as Stratospheric Aerosol Injection, is a geoengineering or climate engineering approach that uses tiny reflective particles or aerosols to reflect sunlight into space in order to cool the planet and reverse or stop global warming.
• It aims to mimic the cooling effects of volcanic eruptions by injecting sulfur dioxide (SO2) directly into the stratosphere, where it forms sunlight-reflecting sulfate aerosols. 
  • The 1991 eruption of Mount Pinatubo in the Philippines, often cited as the inspiration for this concept, deposited massive amounts of particulate matter and sulfur dioxide (SO2) into the atmosphere.
  • This aerosol layer was reported to have lowered average temperatures around the world by about 0.5 °C (0.9 °F) over the following few years. 
• It is believed that as more radiation is scattered in the stratosphere by aerosols, less would be absorbed by the troposphere, the lower level of the atmosphere where weather primarily occurs.
• The production of such an artificial aerosol layer could be accomplished by shooting sulfur particles into the stratosphere with cannons or dispersing them from balloons or other aircraft.

Key Facts about Aerosols

• They are tiny solid or liquid particles suspended in air or a gas.
• Aerosols can be natural, such as fog or gas from volcanic eruptions, or artificial, such as smoke from burning fossil fuels.
• Aerosol particles are either emitted directly into the atmosphere (primary aerosols) or produced in the atmosphere from precursor gases (secondary aerosols).
• Aerosol particles are tiny, but numerous, and often comprise a number of inorganic and organic substances.
• True aerosol particles range in diameter from a few millimicrometres to about 1 micrometre (equal to 10-4 cm). 
• Particles with a diameter of less than 0.1 micrometre are sometimes referred to as Aitken nuclei.
• Visible forms of atmospheric aerosol plumes include smoke, smog, haze, and dust.

What is Stratosphere?

• It is the layer of Earth’s atmosphere lying between the troposphere and the mesosphere. 
• The stratosphere extends from the tropopause at about 10 to 17 km (about 6 to 11 miles) altitude to its upper boundary (the stratopause) at about 50 km (30 miles).
• It’s characterized by a highly stable temperature gradient that cools from top to bottom.
• It also contains the ozone layer.
• Commercial jet aircraft fly in the lower stratosphere to avoid turbulence and increased atmospheric drag, which are common in the troposphere below.
• This layer holds 19 percent of the atmosphere's gases but very little water vapor.

Q1) What is smog?

Smog is a specific type of air pollution. It is a combination of harmful pollutants (often appearing relatively low to the ground as a yellow-brown haze) that are introduced into the atmosphere by both natural and human induced processes.Smog is made up of many chemicals including nitrogen oxides (NOx), sulphur dioxide (SOx), carbon monoxide (CO), and volatile organic compounds (VOCs), but the two main components of smog are particulate matter (PM) and ground-level ozone (O₃).

Source: Climate impact: Water storage projected to decrease across wetter lands around Caspian, Mediterranean seas