The products of photochemical smog are peroxyacetyl nitrate and ozone.
Formation of Photochemical Smog:
Step 1: People begin driving in the morning; nitrogen is burned or oxidised.
N
2 + O
2 
2NO ... (1)
The oxidation number of N
2 is 0. The nitrogen in NO has acquired an oxidation number of +2.
Step 2: After a few hours, NO combines with O
2, in another oxidation reaction.
2NO + O
2 
2NO
2 ... (2)
The nitrogen in NO has an oxidation number of +2. The nitrogen in NO
2 has an oxidation number of +4.
Step 3: Nitrogen dioxide absorbs light energy, resulting in a reduction reaction.
NO
2 
NO + O ... (3)
The nitrogen in NO
2 has an oxidation number of +4 and the nitrogen in NO has an oxidation number of +2.
Step 4: In sunlight, atomic oxygen combines with oxygen gas to form ozone.
O + O
2 
O
3 ... (4)
Step 5: Reaction is temperature and sunlight dependent.
O
3 + NO

NO
2 + O
This self consuming cycle is disrupted when there are unburnt hydrocarbons present in the atmosphere.
NO and NO
2 can also react with the hydrocarbons instead of ozone to form other volatile compounds known as PAN (peroxyacetyl nitrate). The accumulation of ozone and volatile organic compounds along with the energy from the sun forms the brown, photochemical smog seen on hot, sunny days.