Photochemical smog is a resultant of the reaction among
1. NO
2, O
3 and peroxyacetyl nitrate in the presence of sunlight
2. CO, O
2 and peroxyacetyl nitrate in the presence of sunlight
3. CO, CO
2 and NO
2 at low temperature
4. high concentration of NO
2, O
3 and CO in the evening