In environmental science, which of the following gases is commonly recognised as an air pollutant near the ground level?

Introduction / Context:
Air pollution is a major environmental problem that affects human health, ecosystems, and climate. Many gases in the atmosphere are naturally present and harmless at typical concentrations, but some become pollutants when released in large amounts or when they appear near the ground where people breathe. Sulphur dioxide, nitrogen oxides, and ground level ozone are important examples. This question asks you to identify which gas in the given list is commonly recognised and widely taught as a primary air pollutant, especially in the context of emissions from industry and burning of fossil fuels.

Given Data / Assumptions:
- Options include sulphur dioxide, ozone, water vapour, and nitric oxide.
- The focus is on gases that are recognised as air pollutants near the ground.
- Standard school level discussions on air pollution, acid rain, and industrial emissions are assumed.
- The question expects a single best answer rather than several correct choices.

Concept / Approach:
Sulphur dioxide is a major air pollutant released mainly by the burning of coal and oil containing sulphur. It can irritate the respiratory system and contribute to acid rain when it reacts with water and oxygen in the atmosphere. Therefore, it is typically listed as a primary air pollutant in textbooks. Nitric oxide is also an important pollutant, but it is often discussed together with nitrogen dioxide as nitrogen oxides, and some basic level questions emphasise sulphur dioxide more clearly. Water vapour is a natural component of the atmosphere and is not normally treated as a pollutant. Ozone at high altitude protects against ultraviolet radiation, while ground level ozone is a secondary pollutant formed by reactions of other gases; however, in simple multiple choice questions, sulphur dioxide is the most straightforward answer.

Step-by-Step Solution:
1. Recall the main primary gaseous air pollutants: sulphur dioxide, nitrogen oxides, carbon monoxide, and some volatile organic compounds. 2. Recognise that sulphur dioxide is directly emitted from burning fossil fuels, especially coal, in power plants and industries. 3. Understand that water vapour is a naturally occurring gas that cycles through evaporation and condensation and is not normally classified as a pollutant. 4. Note that ozone in the upper atmosphere is beneficial, and ground level ozone is a secondary pollutant formed from other gases, not usually named as the primary pollutant in simple questions. 5. Conclude that sulphur dioxide is the best recognised air pollutant among the given options.

Verification / Alternative check:
Environmental science textbooks and exam preparation guides commonly list sulphur dioxide at the top of the list of gaseous air pollutants. They link it to acid rain and respiratory problems. Charts showing sources and effects of air pollution almost always include sulphur dioxide as an example of a harmful emission from power plants and industrial facilities. While nitrogen oxides and ozone also play roles, they are sometimes discussed in more detail in advanced topics, whereas sulphur dioxide appears as a clear example even at introductory levels.

Why Other Options Are Wrong:
Ozone: In the stratosphere, ozone is beneficial and protects from ultraviolet radiation. At ground level, it can be a secondary pollutant, but in this basic question, sulphur dioxide is a more direct and widely recognised primary pollutant.
Water vapour: This is part of the natural hydrological cycle and is not considered an air pollutant in ordinary environmental discussions.
Nitric oxide: Although it is indeed a pollutant and part of nitrogen oxides, the question context and common teaching materials typically single out sulphur dioxide more clearly.

Common Pitfalls:
Students may pick ozone because they hear about the ozone layer and assume ozone is always harmful, forgetting that high altitude ozone is protective. Another pitfall is to think that any gas involved in climate or weather, such as water vapour, must be a pollutant, which is not correct. To avoid these errors, focus on which gas is most consistently referred to as a primary air pollutant from industrial emissions in basic environmental science, which is sulphur dioxide.

Final Answer:
Among the given options, sulphur dioxide is commonly recognised as an air pollutant near the ground level.