$1) {\mathrm{SO}}_2$: Acid rain, some polluting gases (especially nitrogen oxides and sulphur dioxide) react with the tiny droplets of water in clouds to form sulphuric and nitric acids. The rain from these clouds then falls as acid rain.

$2) \mathrm{PAN}$: Photochemical smog, Peroxyacetyl nitrate $\left(\mathrm{PAN}\right)$ is a phytotoxic air pollutant generated by the reaction of hydrocarbons and nitrogen oxides under action of light. This pollutant can be a restraint of plant growth in closed ecosystems as well as in field.

$3)$ Smoke: Particulate, Smoke particulate matter are a mixture of solid particles and liquid droplets found in the air.

$4){\mathrm{CF}}_2{\mathrm{Cl}}_2$: Stratospheric pollutant, Stratospheric Pollution means depletion of the ozone layer by certain compounds like oxides of nitrogen, chlorofluorocarbons, etc.