Which of the following is primary air pollutants? 

Primary pollutant: Pollutants which are emitted directly from the identifiable sources, either from the natural hazardous events like dust storms, volcanoes, etc or from human activities like burning of wood, coal, oil in homes or industries or automobiles, etc.

The important primary air pollutants are:

1. Oxides of sulphur, particularly the sulphur dioxide (SO2);

2. Oxides of carbon like carbon monoxide (CO) and carbon dioxide (CO2), particularly the carbon monoxide (CO);

3. Oxides of nitrogen, like NO, NO2, NO3 (expressed as NOx);

4. Volatile organic compounds, mostly hydrocarbons; and

5. Suspended particulate matter (SPM).

These primary pollutants often react with one another or with water vapour, aided and abetted by the sunlight, to form entirely a new set of pollutants, called the secondary pollutants.

These are the chemical substances, which are produced from the chemical reactions of natural or anthropogenic pollutants or due to their oxidation, etc., caused by the energy of the sun.

The important secondary pollutants are:

(i) Sulphuric acid (H2SO4);

(ii) Ozone (O3);

(iii) Formaldehydes; and

(iv) Peroxy-acyl-nitrate (PAN); etc.

Primary Pollutants: Co, CO2, SOX, NOX, Aerosols, Bacteria, Pollens, Suspended particulates, Fly ash, Mist, Dew, Mist, Soot, Volcanoes, etc.