AQI’s Limitations in Accurately Reflecting Delhi’s Pollution

Why in the news?

Delhi’s AQI peaked at 500 on November 18, revealing limitations in its ability to effectively measure severe air pollution, especially during extreme PM2.5 concentration levels.

AQI's Limitations in Accurately Reflecting Delhi's Pollution

About the PM2.5 Concentration and AQI:

  • On November 18, 2024, PM2.5 levels in Delhi peaked at 549.6 µg/m³ and 676 µg/m³, with AQI readings at 500.
  • AQI is designed to communicate health risks and not to directly measure pollution levels, which leads to a diminishing return as pollution increases.

How AQI is Calculated:

  • AQI is derived using a formula based on pollutant concentrations. It consolidates data from various pollutants into a single number.
  • The highest sub-index from the pollutants determines the overall AQI for an area.
  • The AQI scale increases in a non-linear manner: small increases in PM2.5 lead to bigger AQI jumps at lower levels, but AQI plateaus beyond 120 µg/m³, particularly in the “very poor” and “severe”

Limitations of AQI:

  • Once PM2.5 concentrations reach extreme levels, such as 380 µg/m³ (AQI 500), the AQI doesn’t reflect further deterioration, which can be misleading.
  • In 2024, Delhi saw 12 severe AQI days and 66 “very poor” days, with three days surpassing AQI 500—higher than the official count.
  • AQI is useful for health alerts but falls short in fully capturing air quality degradation, especially during extreme pollution episodes, thereby failing to adequately communicate urgent risks.
  • The lack of a proactive pollution prevention policy exacerbates the issue, making AQI’s slow response particularly problematic in highly polluted areas like Delhi.

About Commission for Air Quality Management (CAQM):

  • Statutory body formed under the CAQM Act, 2021
  • Aims to improve coordination, research, and solutions for air quality issues in NCR and surrounding areas

Graded Response Action Plan (GRAP)

  • Emergency measures triggered based on AQI thresholds in Delhi-NCR
  • Stages:
    • Grap-I: AQI 201-300 (Advisories, dust control)
    • Grap-II: AQI 301-400 (DG restrictions, enhanced cleaning)
    • Grap-III: AQI 401-450(Construction bans, vehicle entry limits)
    • Grap-IV: AQI >450 (Complete construction halt, school closures, work-from-home)

Air Quality Index (AQI)

  • Simplifies air pollution data into a single number
  • Measures 8 pollutants, including PM2.5 and NO2

Grap Stage IV Restrictions

  • Bans non-essential trucks, BS-IV diesel vehicles
  • Suspends construction, limits vehicle movement
  • Encourages work-from-home, school closures

Sources Referred:

PIB, The Hindu, Indian Express, Hindustan Times

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