PM2.5 Levels in the Indo-Gangetic Plain (IGP)

• 11 Oct 2025

Why in News? 

A recent report by the Centre for Research on Energy and Clean Air (CREA), based on data from the Central Pollution Control Board, ranks Varanasi as the cleanest and Kolkata as the third cleanest city among 17 cities in the Indo-Gangetic Plain (IGP) in terms of PM2.5 concentration. 

Key Points 

• Ranking of Cities by PM2.5 Levels: 
  • Varanasi: Tops the list with the lowest PM2.5 concentration among the cities in the IGP.  
  • Siliguri and Prayagraj: These cities tie for second place in terms of PM2.5 levels.  
  • Kolkata: Ranked third in the IGP, indicating relatively cleaner air compared to many other cities. 
  • Ghaziabad: Worst-polluted city in the IGP with significantly higher pollution levels. 
• Geographic and Meteorological Factors: The IGP is a globally significant air pollution hotspot, attributed to a combination of dense population, intense human activity, and unfavourable weather patterns. 
  • The region experiences dangerously high concentrations of PM2.5 and other pollutants, severely affecting public health and life expectancy. 
  • Kolkata, situated at the eastern extremity of the IGP, experiences trans-boundary air pollution that typically moves from northwest to southeast along the Gangetic valley, contributing significantly to the city's pollution load. 
• National and Regional Air Quality Compliance: Among the 235 cities across India covered by the CREA study, Nandesari (Gujarat) recorded the worst PM2.5 concentration at 89 micrograms per cubic metre, while Karwar (Karnataka) emerged as the cleanest city with just 4 micrograms of PM2.5. 
  • Delhi ranked 28th nationally with a moderate pollution level of 36 micrograms per cubic metre. 
• National Clean Air Programme: Of the 93 cities part of this programme, including Kolkata, all met the National Ambient Air Quality Standard (NAAQS) of 40 micrograms per cubic metre, indicating a positive trend in air quality improvements. 
  • However, only 32 cities complied with the more stringent World Health Organisation (WHO) limit of 15 micrograms per cubic metre. 

Air Pollution

• About:  Air pollution encompasses the presence of solids, liquids, gases, noise, and radioactive radiation in the atmosphere, at concentrations harmful to humans, living organisms, property, or environmental processes.  
  • These substances, known as pollutants, can be either natural or human-made and can originate from various sources such as industrial processes, vehicle emissions, agricultural activities, and natural events like wildfires and volcanic eruptions.  
• Particulate Matter (PM): PM refers to a complex mixture of extremely small particles and liquid droplets suspended in the air. These particles come in a wide range of sizes and can be made up of hundreds of different compounds.  
  • PM10 (coarse particles): Particles with a diameter of 10 micrometres or less.  
  • PM2.5 (fine particles): Particles with a diameter of 2.5 micrometres or less.