If it's a calm humid day, the ammonia will combine with moisture to form a vapor that's heavier than air, so it will settle to the ground instead of dissipating

If it's a calm humid day, the ammonia will combine with moisture to form a vapor that's heavier than air, so it will settle to the ground instead of dissipating. That means if you have even a tiny leak from the pump nozzle, over time it would accumulate in low-lying areas like basements.