Why can ammonia cause both a smell sensation and an irritating sensation?

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Compound eye — Senses Vespid wasps (Vespidae), similar to other insects, have compound eyes that consist of thousands of tiny optical units known as ommatidia, which contain light-sensitive photoreceptor cells.

Ammonia can cause both a smell sensation and an irritating sensation because it stimulates two distinct types of nerve endings within the nasal cavity.1

The olfactory receptors, located high in the nasal cavity, are responsible for the sense of smell by detecting airborne chemicals. Simultaneously, pain endings of the trigeminal nerve are widely distributed throughout the nasal lining. While many substances primarily trigger the olfactory system, potent chemicals like ammonia are capable of stimulating both the specialized olfactory receptors and these trigeminal nerve endings. The stimulation of the trigeminal nerve is what produces the characteristic sensation of irritation.21