Which of the following is a secondary pollutant?

Secondary pollutants are pollutants that form in the atmosphere. Pollutants emitted from different sources react with molecules in the atmosphere to form new pollutants.

Some of the secondary pollutants are:

1.    Sulphuric acid and nitric acid (a component of acid rain)

2.    Particulate matter.

3.    Nitrogen dioxide (NO₂)

4.    Peroxyacyl nitrates (PANs)

Secondary air pollutants create health problems such as reduced respiratory function and eye irritation etc.,