Which of the following statement about pollutants is incorrect ?

• A

  ${\mathrm{SO}}_3$ is a primary pollutant and it is also a component of classical smog

• B

  $\mathrm{NO}$is a primary pollutant and it is also a component of photochemical smog

• C

  ${\mathrm{CH}}_4$is a primary pollutant and also a green house gas

• D

  $\mathrm{PAN}$is a secondary pollutant and a component of Los Angles smog