Explanation:

4th option is correct.
Secondary pollutants are not emitted directly.
Peroxyacetyl nitrate is a peroxyacyl nitrate. It is a secondary pollutant present in photochemical smog. It is thermally unstable and decomposes into peroxyethanoyl radicals and nitrogen dioxide gas. It is a lachrymatory substance. Peroxyacetyl nitrate, or PAN, is an oxidant that is more stable than ozone.