Which of the following pollutants is considered a surrogate for eye irritation?

Ozone is treated as a surrogate indicator for eye irritation from photochemical air pollution.

Its level tracks the oxidising smog mixture that makes eyes water and sting.

Nitrogen dioxide chiefly affects the lungs and airways rather than serving as an eye irritation marker.

Sulphur dioxide irritates the respiratory tract and is not the standard eye irritation surrogate.

Carbon monoxide is a colourless asphyxiant that does not stand in for eye irritation.

Peroxyacetyl nitrate in the same smog is a particularly strong direct eye irritant.