Natural sources of air pollution Which of the following is <em>not</em> a natural source of air pollution (i.e., the odd one out)?

Introduction / Context:
Air pollution has both natural and anthropogenic sources. Recognising natural contributors is important for background level estimation, air quality modelling, and setting realistic regulatory targets. The task is to identify which listed item is not natural.

Given Data / Assumptions:

• We assess each option for natural origin.
• Processes such as volcanoes, lightning, biogenic emissions, and sunlight-driven reactions can occur without human activity.

Concept / Approach:
Volcanic eruptions emit gases and particulates naturally. Lightning fixes nitrogen and forms oxidants episodically. Biological decay releases methane, VOCs, and other compounds. Photochemical oxidation of organic matter occurs when sunlight drives reactions among naturally emitted VOCs and background oxidants. Therefore, all listed items are indeed natural sources or processes. The correct answer is “None of these,” meaning none is exclusively non-natural.

Step-by-Step Solution:

Verification / Alternative check:
Baseline atmospheric measurements in remote regions show natural contributions from sea spray, dust, biogenic VOCs, volcanic sulphur, and lightning-produced nitrogen oxides, even in the absence of human activity.

Why Other Options Are Wrong:

• Each individual option (a), (b), (c), and (e) describes a process that naturally emits pollutants or precursors.

Common Pitfalls:
Assuming “photochemical oxidation” is strictly anthropogenic; in reality, biogenic VOCs undergo sunlight-driven chemistry naturally, though human emissions can intensify it.

Final Answer:
None of these