What is Ozone?

1. Introduction to Ozone (O₃)
Ozone (O₃) is a molecule composed of three oxygen atoms. It exists in two distinct layers of the atmosphere with contrasting effects on health and the environment:

• ​Stratospheric Ozone: Located 10–30 miles above Earth, it forms a protective layer absorbing harmful ultraviolet (UV) radiation.
• ​Tropospheric (Ground-Level) Ozone: A secondary pollutant formed when nitrogen oxides (NOx) and volatile organic compounds (VOCs) react in sunlight. It is a key component of smog.

2. Health Effects of Stratospheric Ozone Depletion
Depletion of the ozone layer, primarily due to chlorofluorocarbons (CFCs), increases UV-B and UV-C radiation reaching the Earth’s surface. Health impacts include:

• ​Skin Cancer: Elevated risk of melanoma and non-melanoma cancers.
• ​Eye Damage: Increased cataracts and photokeratitis (snow blindness).
• ​Immune Suppression: Reduced resistance to infections.
• ​Mitigation: The Montreal Protocol (1987) has successfully phased out CFCs, aiding ozone layer recovery.

3. Health Effects of Ground-Level Ozone
Exposure to tropospheric ozone primarily affects the respiratory system but can have broader impacts:

• ​Acute Effects:
  • Respiratory irritation (coughing, throat soreness).
  • Asthma exacerbation and increased medication use.
  • Reduced lung function and shortness of breath.
• ​Chronic Effects:
  • Persistent inflammation leading to chronic obstructive pulmonary disease (COPD).
  • Impaired lung development in children, as shown in longitudinal studies.
• ​Vulnerable Groups: Children, the elderly, outdoor workers, and individuals with pre-existing respiratory or cardiovascular conditions.
• ​Cardiovascular Impacts: Indirect stress from lung inflammation may exacerbate heart conditions.

4. Environmental and Indirect Health Effects

• ​Ecosystem Damage: Ozone reduces crop yields (e.g., wheat, soybeans), threatening food security.
• ​Climate Interaction: Higher temperatures from climate change may increase ozone formation, creating a feedback loop.

5. Mitigation and Prevention

• ​Regulations: The EPA’s National Ambient Air Quality Standards (NAAQS) set ozone limits (0.070 ppm over 8 hours). The WHO recommends a guideline of 100 μg/m³ (8-hour mean).
• ​Emission Reductions: Targeting NOx and VOCs from vehicles, industries, and power plants.
• ​Personal Protection: On high ozone days (AQI > 100), limit outdoor activities, especially during afternoon hours.

6. Conclusion
While stratospheric ozone recovery is a success story, ground-level ozone remains a critical public health challenge. Addressing it requires global cooperation to reduce precursor emissions and adapt to climate-related changes. Continued research and policy efforts are essential to safeguard both human health and ecosystems.

References: EPA, WHO, American Lung Association, and studies on pediatric lung function (e.g., Children’s Health Study).

This structured approach clarifies the dual role of ozone, emphasizing the importance of context in understanding its health impacts.