Cloud Seeding

Syllabus: GS3/Environment

Context

• Delhi Chief Minister has said cloud seeding is essential for the national capital as it could play a key role in controlling rising pollution levels during the winter season.

Why is Delhi’s Air Quality Severe in Winter?

• Temperature Inversion: During winter, the air near the ground becomes cooler than the air above it.
  • This inversion layer traps pollutants (such as particulate matter and gases) close to the surface, preventing their vertical dispersion into the upper atmosphere.
• Low Wind Speeds: Winds are generally weaker in winter, which reduces horizontal dispersion of pollutants, allowing them to accumulate in the lower atmosphere.
• Crop Residue Burning: Each year, post-harvest stubble burning in neighbouring states like Punjab, Haryana, and western Uttar Pradesh releases large amounts of smoke and particulate matter.
  • Prevailing wind patterns carry this pollution towards Delhi, worsening air quality.
• Dust and Urban Pollution Entrapment: Urban dust and vehicular emissions linger longer in the atmosphere due to low boundary layer height in winter, compounding the pollution problem.

What is Cloud Seeding?

• Cloud seeding is a weather modification method to enhance a cloud’s ability to produce rain or snow.
• History: First demonstrated in 1946 by Vincent J. Schaefer, an American chemist and meteorologist.
• Seeding Agents: Clouds are usually injected with salts like silver iodide, potassium iodide, or sodium chloride to trigger condensation.
  • Silver iodide and dry ice (solid CO2) – effective in supercooled clouds (below freezing). 
  • Calcium chloride – used for warmer clouds (above freezing).
• Working Principle: The salts, or the seeding agents, serve as nuclei around which water droplets can form or ice can crystallise.
  • As water droplets grow, they collide with others in the cloud. As they become heavy, the cloud gets saturated and it rains.
  • Meteorologists identify clouds for seeding which have sufficient moisture but are unable to produce enough precipitation on their own.
• Methods of Delivery: These particles are dispersed into clouds using special aircraft, rockets, or dispersion devices kept on the ground.

Can Cloud Seeding Help in Combating Air Pollution?

• Dependence on Natural Cloud: Cloud seeding depends on natural clouds; it can’t create them.
  • And even when clouds exist, the evidence that seeding reliably increases rainfall remains weak and contested. 
• Impact on Pollution: When it rains and reduces pollution, the respite is temporary, the pollution levels go back up within a day or two.
• Efficiency: Fine particulate matter (PM 2.5) and PM10 get washed away with prolonged precipitation.
  • However, there is no impact on other pollutants such as ozone and sulphur dioxide.

What can be Other Measures?

• Root Causes Identified by Science: Long-standing scientific consensus attributes hazardous air quality to emissions from vehicles, industries, power plants, construction, waste burning, and agricultural stubble fires.
• Known Long term Solutions: Cleaner transport systems (electric mobility, public transport, emission norms).
  • Sustainable energy transition (phasing out coal, promoting renewables).
  • Effective waste management and dust control in construction.
  • Urban planning that minimizes congestion and reduces pollution sources.
• Focus on Quick Fixes: There is an increasing reliance on temporary measures like smog towers, artificial rain, or short-term bans though they are effective in short terms. 
• The Need for Evidence-Based, Ethical Action: Real change demands systemic reforms and long-term enforcement of emission controls.

Source: TH