Sources of ozone generation in air Which of the following is NOT a source that generates ozone in the surrounding atmosphere during normal operation?

Introduction / Context:
Ozone (O3) can be intentionally produced (e.g., in sterilisation) or incidentally formed by electrical discharges and strong ultraviolet radiation acting on oxygen. Understanding everyday sources helps in indoor air quality assessments and occupational safety planning.

Given Data / Assumptions:

• We are concerned with routine operation, not accidental fires or failures.
• Devices known for corona discharge or strong UV can create ozone locally.
• Household refrigerators are considered in normal working condition.

Concept / Approach:
Photocopiers and laser printers can generate ozone via corona discharge in their high-voltage sections. High-voltage electrical equipment (transformers, Tesla coils) also forms ozone around sparks/corona. Dermatological phototherapy equipment may emit UV wavelengths capable of producing ozone in room air if not fully contained or filtered. In contrast, refrigerators do not create ozone; historic concerns with them were about refrigerants (e.g., CFCs) depleting stratospheric ozone after release, not generating ozone locally in rooms.

Step-by-Step Solution:

Verification / Alternative check:
Indoor air quality guidance notes commonly cite photocopiers and high-voltage devices as incidental ozone sources; refrigerators are not on such lists.

Why Other Options Are Wrong:

• Xerox machines: Known incidental ozone producers; many contain ozone filters.
• Dermatological phototherapy: Produces strong UV; can generate ozone if unfiltered.
• High-voltage equipment: Corona discharge readily forms ozone.
• Ozone generators: Deliberately produce ozone for treatment; obviously a source.

Common Pitfalls:
Confusing “ozone depletion” (a stratospheric chemistry issue) with “ozone generation” (local indoor air emission), which are distinct phenomena.

Final Answer:
Refrigerators