32. Correct statement regarding the effect of ozone on biosphere is
    (1) Both atmospheric and stratospheric ozone is beneficial
    (2) Both atmospheric and stratospheric ozone is harmful
    (3) Atmospheric ozone is harmful but stratospheric ozone is beneficial
    (4) Atmospheric ozone is beneficial but stratospheric ozone is harmful

Ozone (O₃) plays a dual role in Earth’s atmosphere, with effects on the biosphere that are entirely dependent on its location. Stratospheric ozone is critical for protecting life by absorbing harmful ultraviolet (UV) radiation, while atmospheric (ground-level) ozone is a major air pollutant that can damage human health, crops, and ecosystems. Understanding the difference between these two forms of ozone is essential for environmental science and public health. This article explores the correct statement regarding the effect of ozone on the biosphere, the formation and function of ozone in different atmospheric layers, and the consequences of ozone pollution and depletion.

The Dual Nature of Ozone

Ozone is a molecule composed of three oxygen atoms (O₃). Its impact on the biosphere is determined by where it is found in the atmosphere:

• Stratospheric Ozone: Located in the upper atmosphere (stratosphere), this “good” ozone forms a protective layer that absorbs most of the Sun’s harmful UV radiation.

• Atmospheric (Ground-Level) Ozone: Found in the lower atmosphere (troposphere), this “bad” ozone is a harmful pollutant that negatively affects human health and the environment.

Stratospheric Ozone: The Protective Shield

Stratospheric ozone is concentrated in a layer approximately 15 to 30 kilometers above the Earth’s surface. This ozone layer is crucial for life on Earth because it absorbs the majority of the Sun’s ultraviolet-B (UVB) radiation, which can cause skin cancer, cataracts, and harm to plants and marine life.

Formation and Function

• Formation: Stratospheric ozone is produced when ultraviolet light breaks apart oxygen molecules (O₂) into individual oxygen atoms, which then combine with other oxygen molecules to form ozone (O₃).

• Protective Role: The ozone layer filters out most of the Sun’s harmful UVB rays, preventing them from reaching the Earth’s surface and protecting all forms of life from DNA damage and other harmful effects.

• Stability: The amount of stratospheric ozone remains relatively stable over time, though human activities (such as the release of chlorofluorocarbons) have led to temporary depletion in certain regions, most notably the “ozone hole” over Antarctica.

Atmospheric (Ground-Level) Ozone: A Harmful Pollutant

Atmospheric ozone at ground level (in the troposphere) is a secondary pollutant formed by chemical reactions between nitrogen oxides (NOx) and volatile organic compounds (VOCs) in the presence of sunlight. Unlike stratospheric ozone, ground-level ozone is not beneficial to the biosphere.

Formation and Effects

• Formation: Ground-level ozone is created when pollutants from vehicles, power plants, industrial facilities, and other sources react in sunlight.

• Health Impacts: Exposure to ground-level ozone can cause respiratory problems such as coughing, throat irritation, chest pain, and worsening of asthma, bronchitis, and emphysema.

• Environmental Impacts: High concentrations of ground-level ozone can damage crops, forests, and ecosystems by inhibiting plant growth and reducing agricultural yields.

• Urban Smog: Ground-level ozone is a major component of urban smog, contributing to poor air quality in cities and industrial areas.

Comparing the Options

Let’s review the statements in the context of ozone’s effects on the biosphere:

• Both atmospheric and stratospheric ozone is beneficial:
  Incorrect. Only stratospheric ozone is beneficial; ground-level (atmospheric) ozone is harmful.

• Both atmospheric and stratospheric ozone is harmful:
  Incorrect. Stratospheric ozone is beneficial; ground-level ozone is harmful.

• Atmospheric ozone is harmful but stratospheric ozone is beneficial:
  Correct. This accurately reflects the dual role of ozone in the atmosphere.

• Atmospheric ozone is beneficial but stratospheric ozone is harmful:
  Incorrect. The opposite is true: stratospheric ozone is beneficial, and ground-level (atmospheric) ozone is harmful.

The Science Behind Ozone’s Dual Role

The reason for ozone’s dual role lies in its location and the processes that create it:

• Stratospheric Ozone:

  • Formed by natural processes involving sunlight and oxygen.

  • Acts as a shield against harmful UV radiation.

  • Essential for the survival of life on Earth.

• Ground-Level (Atmospheric) Ozone:

  • Formed by chemical reactions involving pollutants and sunlight.

  • Acts as a pollutant that damages health and ecosystems.

  • A major contributor to air quality problems.

Consequences of Ozone Depletion and Pollution

• Ozone Depletion in the Stratosphere:

  • Increases UV radiation reaching the Earth’s surface.

  • Leads to higher rates of skin cancer, cataracts, and harm to marine and terrestrial ecosystems.

• Ground-Level Ozone Pollution:

  • Causes respiratory and cardiovascular health problems.

  • Reduces agricultural productivity and damages natural ecosystems.

Key Takeaways

• Stratospheric ozone is beneficial: It protects life by absorbing harmful UV radiation.

• Ground-level (atmospheric) ozone is harmful: It is a major air pollutant that damages health and the environment.

• The correct statement is: Atmospheric ozone is harmful but stratospheric ozone is beneficial.

• Understanding ozone’s dual role is essential for environmental protection and public health.

Summary Table

Conclusion

The correct statement regarding the effect of ozone on the biosphere is:
Atmospheric ozone is harmful but stratospheric ozone is beneficial.
Stratospheric ozone forms a protective shield that filters out harmful UV radiation, while ground-level (atmospheric) ozone is a dangerous pollutant that harms human health and the environment. Recognizing this dual role is crucial for addressing both ozone depletion and air pollution challenges.

In summary, the correct answer is:
(3) Atmospheric ozone is harmful but stratospheric ozone is beneficial.
This distinction is fundamental to understanding ozone’s impact on life on Earth and guiding efforts to protect the environment and public health.