Photochemical Smog:

Photochemical  smog, a  secondary Pollutant,  results when  the two pollutants, nitrogen  oxide and hydrocarbons  found  in  automobile exhausts, react with  one another  in the presence of  sunlight to produce  nitrogen  dioxide (N0₂), ozone (0₃) and a  compound called  PAN (Peroxylacetyl nitrate), which  then appear as a yellowish  brown  haze.  Breathing ozone affects  the respiratory and nervous  system. It causes respiratory  distress, affects eye membranes and stimulates tears. It also causes headache. Ozone also damages rubber  articles, textiles and discolours paintings. It has been  recently found  that smog is harmful  to timber.  PAN is especially damaging to plants.  Plants exposed  to PAN exhibit  leaf mottling  and