What does glazing, silvering, or bronzing on the underside of a leaf indicate?

The presence of glazing, silvering, or bronzing on the underside of a leaf typically indicates damage from peroxyacyl nitrates (PANs). These compounds are secondary pollutants formed from the photochemical reactions of volatile organic compounds (VOCs) and nitrogen oxides in the atmosphere, especially under conditions of sunlight and heat.

When plants experience exposure to PANs, their physiology is affected in such a way that results in these distinctive leaf symptoms. This form of damage is often associated with urban areas where vehicle emissions and industrial activities release the precursors necessary for PAN formation. Understanding the specific symptoms on foliage helps in identifying the type of pollutant causing the damage, and this particular indication is crucial for environmental health specialists and sanitarians in assessing air quality and its potential effects on vegetation.