This is unique to the Rao book.
Are you researching this for a specific , thesis , or engineering design project ?
Formed in the atmosphere through chemical reactions between primary pollutants and environmental factors like sunlight (e.g., photochemical smog, ozone ( O3cap O sub 3 ), and acid rain).
After mastering Rao, move on to Fundamentals of Air Pollution by Vallero, or Air Pollution Control Engineering by Noel de Nevers for an advanced global perspective.