WHAT IS SMOG? TYPES OF SMOG.

• Smog is a man made harmful pollutants combination. It is a mixture of smoke and fog into air. It is a mixture of various gases with water vapor.
• There are two types of smog exist.

1. Sulphurous smog or reducing smog
2. Nitrogenous smog or photo-chemical smog

1. Sulphurous smog or reducing smog :

•  It is a mixture of smoke, fog and sulphur dioxide. This smog affects the london city very badly for several years after the introduction of coal and fuel. So it is also known as London smog.
• The component of sulphurous smog:

1. Oxide of sulphur
2. Particulate matter which are coming from smoke
3. Humidity or water from fog

Formation process of sulphurous smog :

• Sulphurous smog occurs mainly in the early morning hours in winter where there is relatively high humidity in the absence of winds and stable atmospheric zone, the chemical reaction take place in the presence of sunlight in the early morning.                                                                   S + O2          -----    SO2                                                     2SO2 + O2        -----    2SO3
• The reaction takes place by oxidation and particulate matter. The SO2 combines with moisture present in fog to form sulphuric acid H2SO3. This acid is again oxidized and form sulphuric acid H2SO4 and this combines with NH3 present in smoke to form ammonium salt [(NH4)2SO4].
•                      SO2  +  H2O ---- H2SO3                                                      2H2SO3 + O2  ----  2H2SO4                                              H2SO4  +  2NH3  ---- [(NH4)2SO4]
• This type of smog are not photo-chemical in nature.
• This smog can affect the throat of human being.

2. Nitrogenous smog :

• The main component of this kind of smog is oxides of nitrogen. So it is called nitrogenous smog. It is not consists smoke and fog. During the formation of this type of smog, photo-chemical reactions are take place. So, it is known as a photo-chemical smog. This smog is first appears in los-angles. so it is also called los-angles smog.
• The main compounds present in this type of smog are :

1. Oxides of nitrogen
2. Tropospheric ozone
3. Hydrocarbon
4. Photoradiation

Formation of nitrogenous smog or photo-chemical smog

• Photo-chemical smog is an example of secondary air pollutant because it results from the interaction of nitrogen oxide and nitrogen dioxide.
• NO and NO2 both are primary pollutants. When the both interact with ultraviolet rays, the result is photo-chemical smog. The interaction among hydrocarbons, oxides of nitrogen and sunlight produces new component that are harmful for humans.
• The two most damaging king of materials formed are ozone O3 and PAN (peroxy acetyl nitrates). Ozone is harmful because it destroys chlorophyll and injures lung tissue and PAN is harmful because it causes inflammation is respiration activity and eye irritation. 

Formation of peroxy acetyl nitrate :

• NO reacts with free oxygen in atmosphere and convert in nitrogen dioxide NO2.                                                                        NO  + O2 --- NO2
•  Now this NO2 absorb energy from the sun and breaks up NO2 nitrogen dioxide and again convert it into nitric oxide and free oxygen molecule.                                                      NO2 ----  NO+ O
• The oxygen molecule are very reactive with O2 which present in air and start producing ozone O3.                                    O  +  O2 ----  O3
• The ozone reacts rapidly with NO which is produce in second equation and regenrate NO2.
• O3 and NO2 both are toxic gases. They reacts with each other in the presence of unburnt hydrocarbon in pollutant air and produce peroxy acetyl nitrate.