Ground-level ozone (O₃)

Why in News?

According to the Centre for Science and Environment (CSE), analysis of data from the Continuous Ambient Air Quality Monitoring System (CAAQMS) showed that the National Ambient Air Quality Standard (NAAQS) for 8-hour average ground-level ozone (100 µg/m³) was exceeded every day between March 1 and May 31, 2025 in several locations across the Delhi-NCR.

• The findings indicate that ozone pollution is becoming a major air quality challenge alongside particulate pollution.

What is Ground-Level Ozone?

• Ground-level ozone (O₃) is a secondary air pollutant, meaning it is not emitted directly from any source.
• It is formed through photochemical reactions between: Nitrogen Oxides (NOx) and Volatile Organic Compounds (VOCs).
• These pollutants mainly originate from automobile exhausts, industrial emissions, power plants, and solvent use.
• In the presence of strong sunlight and high temperatures, NOx and VOCs react to produce ozone.

Why is Ozone Pollution Increasing?

• High summer temperatures accelerate photochemical reactions.
• Intense solar radiation promotes ozone formation.
• Vehicular emissions continue to supply NOx and VOCs.
• Climate change is expected to worsen ozone pollution by increasing the frequency of hot days and heatwaves.

Health Impacts of Ground-Level Ozone

• Ground-level ozone is a highly reactive oxidant gas that damages the respiratory system.
• Acute Health Effects: cough, throat irritation, chest tightness, wheezing, shortness of breath (dyspnea), pain during deep breathing.
• Effects on the Respiratory SystemL injures airway epithelium, causes airway inflammation, increases airway permeability etc.
• Impacts Lung Function.
• Strongly associated with asthma attacks (exacerbations), increased hospital admissions etc..

Source: DTE

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