Atmospheric Chemistry – Composition of the ozone layer At stratospheric heights where the ozone layer exists, which mixture of oxygen species is present due to photochemical reactions?

Introduction / Context:
The stratospheric ozone layer protects life by absorbing much of the Sun’s biologically harmful ultraviolet radiation. Its chemistry is dynamic: ultraviolet photons continuously split and recombine oxygen species, establishing a balance known as the Chapman cycle (with catalytic modifiers).

Given Data / Assumptions:

• The question asks which oxygen species coexist at altitude.
• Photolysis and recombination processes are active in sunlight.
• We focus on the principal constituents related to ozone chemistry.

Concept / Approach:
Under UV radiation, O2 absorbs energy and splits into atomic oxygen O. These O atoms recombine with O2 to form ozone O3. Conversely, O3 can photodissociate back to O2 and O. Therefore, a mix of O, O2, and O3 coexists in the ozone layer, with relative concentrations depending on altitude, sunlight, and catalytic cycles involving species like NOx, HOx, and ClOx.

Step-by-Step Solution:
Recognize ongoing photochemistry: O2 + UV → 2O; O + O2 + M → O3 + M; O3 + UV → O2 + O.Infer coexistence: all three oxygen forms appear in steady-state proportions.Select the option naming the full mixture.

Verification / Alternative check:
Standard atmospheric profiles show peak ozone mixing ratios in the lower stratosphere, with measurable O and abundant O2 present, supporting the mixed-species description.

Why Other Options Are Wrong:

• only O3 or only O2: oversimplify the active photochemical environment.
• O + O2 only: omits ozone, the defining species of the layer.

Common Pitfalls:
Thinking of the ozone layer as pure ozone; in reality, ozone is a trace gas amidst predominant O2 and coexisting reactive O atoms.

Final Answer:
mixture of atomic oxygen (O), ordinary oxygen (O2) and Ozone (O3)