PAN is included in the class of smog pollutants called oxidants. Most of these oxidants are ozone molecules. Oxidants are oxidizers, which are substances that give up oxygen atoms to other substances, such as the linings of your respiratory system.

It does not take much PAN to cause a lachrymating effect. Ozone needs to be about 0.1 ppmv (or 100 ppbv) to achieve the same effect in sensitive people.