Asphyxiant in air — toxicology threshold Which pollutant causes death by asphyxiation if its concentration in atmospheric air exceeds the maximum allowable level (greater than about 50 ppm)?

Introduction / Context:
Asphyxiants interfere with oxygen delivery to tissues. Recognizing the most dangerous low-level asphyxiant in urban air is essential for safety, environmental monitoring, and public health.

Given Data / Assumptions:

• The threshold mentioned (~50 ppm) is an order-of-magnitude cue for acute concern.
• Candidates include carcinogens, oxidants, and a well-known hemoglobin-binding gas.

Concept / Approach:
Carbon monoxide (CO) binds hemoglobin with much higher affinity than oxygen, forming carboxyhemoglobin and reducing blood’s oxygen-carrying capacity. Even tens of ppm for prolonged exposure can cause symptoms; higher concentrations lead to loss of consciousness and death. The others listed are harmful but do not produce classic hemoglobin-related asphyxiation at such low ppm levels.

Step-by-Step Solution:

Verification / Alternative check:
Toxicology references list exposure guidelines and health effects for CO, showing rapid onset of hypoxia symptoms as concentrations rise above tens to hundreds of ppm.

Why Other Options Are Wrong:

Common Pitfalls:
Assuming any toxic gas at 50 ppm causes asphyxiation; the unique hemoglobin affinity of CO makes it particularly dangerous.

Final Answer:
Carbon monoxide