Which of the following best defines a point source in air pollution regulation?

• A. A single, identifiable discharge point, such as a smokestack from a power plant.
• B. Diffuse sources without a discrete discharge point.
• C. Emissions from mobile sources only.
• D. Air emissions from a city as a whole.

Answer: (A)

A point source in air regulation means a single, identifiable discharge point where pollutants enter the atmosphere. This is the hallmark that lets regulators link emissions to a specific facility and set enforceable limits, perform stack tests, or use continuous emission monitoring. A smokestack from a power plant is the classic example. This concept differs from diffuse or area sources, which don’t have one discrete discharge point, and from mobile sources, which move and can’t be tied to a fixed location. Emissions from an entire city also aren’t a point source because they come from many locations across an area rather than one stack.