The pollutants which come directly in the air from sources are called primary pollutants. Primary pollutants are sometimes converted into secondary pollutants. Which of the following belongs to secondary air pollutants

Peroxyacetyl nitrate (PAN) and ozone are the two important secondary photochemical air pollutants found in the urban atmosphere  of the two, PAN is the more useful indicator of photochemical reactions in polluted air as, unlike ozone, it appears to have no large natural source