Which one of the following air pollutants combines strongly with haemoglobin in human blood, reducing its oxygen carrying capacity and potentially causing suffocation and death?

Introduction / Context:
Air pollutants affect human health in different ways. Some irritate the respiratory tract, others cause long term diseases, and certain gases interfere directly with the blood ability to carry oxygen. This question focuses on identifying the pollutant that binds with haemoglobin in red blood cells, reducing oxygen transport and leading to symptoms of suffocation and even death in severe exposures.

Given Data / Assumptions:

• The pollutants listed are chlorofluorocarbons, fly ash, carbon monoxide, and sulphur dioxide.
• The key effect described is binding to haemoglobin and reducing its oxygen carrying capacity.
• We assume a basic understanding of how haemoglobin carries oxygen in the blood.

Concept / Approach:
Haemoglobin (Hb) is a protein in red blood cells that binds oxygen in the lungs and releases it in tissues. Carbon monoxide (CO) is a colourless, odourless gas produced when carbon based fuels burn incompletely, such as with faulty heaters, vehicle exhaust in closed spaces, or poorly ventilated fires. Carbon monoxide binds to haemoglobin with an affinity much higher than that of oxygen, forming carboxyhaemoglobin (COHb). This binding prevents haemoglobin from carrying oxygen, leading to tissue hypoxia. Even relatively low concentrations of CO can cause headache, dizziness, and weakness, and higher concentrations can cause loss of consciousness and death. Chlorofluorocarbons mainly affect the ozone layer and act as greenhouse gases; they do not bind haemoglobin in this way. Fly ash consists of particulate matter that can damage lungs but does not chemically bind haemoglobin. Sulphur dioxide irritates the respiratory tract and contributes to acid rain but does not have the specific strong binding to haemoglobin that carbon monoxide does. Therefore, carbon monoxide is the correct answer.

Step-by-Step Solution:

Verification / Alternative check:
Toxicology and environmental health references describe carbon monoxide poisoning as a major risk in enclosed spaces with defective heating systems or vehicle exhaust accumulation. They explain that the key mechanism of toxicity is the formation of carboxyhaemoglobin, which greatly reduces the blood capacity to carry oxygen. Symptoms and treatment guidelines (such as administration of 100 percent oxygen or hyperbaric oxygen) are based on this mechanism. Air quality standards for carbon monoxide are set specifically to prevent dangerous levels of carboxyhaemoglobin in the population. These facts confirm that the pollutant in question is carbon monoxide.

Why Other Options Are Wrong:

Chlorofluorocarbons used as refrigerants and propellants are wrong because they mainly affect the ozone layer and climate, not haemoglobin binding.

Fly ash particles released from burning coal are incorrect because they consist of fine solid particles that cause respiratory problems but do not chemically bind to haemoglobin.

Sulphur dioxide gas released from burning sulphur rich fuels is also wrong because it primarily irritates airways and contributes to acid rain; it does not form a strongly bound complex with haemoglobin that blocks oxygen transport in the same manner as carbon monoxide.

Common Pitfalls:
Students may confuse the many harmful effects of different pollutants and think that any toxic gas might bind haemoglobin. Another common error is to associate carbon monoxide only with traffic pollution and forget its specific biochemical action. To answer accurately, focus on the phrase combines with haemoglobin and reduces its oxygen carrying capacity. This description is characteristic of carbon monoxide poisoning through formation of carboxyhaemoglobin, making carbon monoxide the correct option.

Final Answer:
Thus, the air pollutant that binds strongly with haemoglobin and reduces blood oxygen carrying capacity is carbon monoxide gas produced by incomplete combustion.