What is the main concern with higher concentrations of NH3?

The main concern with higher concentrations of NH3, or ammonia, is multifaceted, which is why the choice indicating "all of the above" is the correct answer.

When ammonia levels rise, corrosion of metals can become a significant issue. Ammonia is known to be corrosive, particularly to metals such as copper and brass, leading to damage and potential failures in piping systems and equipment. This can result in costly repairs and safety hazards.

In addition to corrosion, ammonia presents an odor nuisance. Even at low concentrations, ammonia has a very strong, pungent smell that can be unpleasant and can lead to discomfort for anyone working in or around an area with high ammonia levels. This odor issue can affect workplace morale and overall comfort.

Furthermore, health hazards to humans are a serious concern with higher concentrations of ammonia. Exposure to elevated levels can lead to respiratory problems, irritation of the eyes, skin, and mucous membranes, and can even result in more severe health effects with prolonged exposure or in sensitive individuals, such as those with pre-existing health conditions.

Given these significant aspects—corrosion, odor, and health risks—the correct understanding encompasses all these concerns, justifying why the answer that includes all these factors is appropriate.