The answer is Neither toxic air pollutants nor loud engine noise is a problem for food cart operators who use curbside charging stations instead of gasoline-powered generators.
Explanation:
An error in subject-verb agreement occurs if a singular subject is followed by a plural verb or vice-versa, considering the subject and verb should always agree in number. In the case of one singular and one plural subject connected by the conjunction neither/nor, the common recommendation is that the verb agrees with the second noun or the noun closer to the verb. In the sentence presented this noun is "loud engine noise" which is a singular noun and therefore the correct verb form should be "is" which is singular rather than "are" which is the plural form.
