What Is Smog?

The smog is basically a combination of smoke and fog. In other words it is known as air pollution. Sources of
  smog include emissions

• industry,
• motor vehicles,
  
• burning
  
• barbecues
• construction
  
• factories
  
• gasoline and diesel powered vehicles
  
• pesticides
  
• pollutants carried by the wind etc.
  

As smog is present in the air so both urban and rural regions might face smoggy days.

As said before  it is thought to be smoke air pollution held down close to the ground by fog or moisture in the air....smog

Smog is air pollution.  It occurs when an abundance of particulates in the air creates impaired visibility and result in a rise in human health problems including asthma.  Smog can be formed naturally by volcanoes – this is also known as vog – but it can also be formed by a variety of industrial pollutants. Although many people point to cities like Los Angeles where a visible layer of smog can sometimes be seen sitting menacingly over the city centre, the most dangerous part of smog is often invisible and is only detectable with specialized scientific instruments.

The term smog was coined by Harold Antoine des Voeux when he needed a word to describe the heavy fog that was, at the time, unique to London.  The year was 1905 and he created an index of fogs and smokes that were adopted by the media who were well aware that London’s smog problem had been noted by residents and visitors since the beginning of the industrial resolution.  The industrial smog des Voeux had categorized was caused by the combustion of materials including coal.

Photochemical smog is the type that hangs over modern day LA and is caused by a chemical reaction between oxygen, hydrocarbons, and other particular matter present in the atmosphere.  If conditions are right, these particles will form ozone and nitrous oxide when they oxidize.  In LA the smog is a direct result of a combination of lots of sunshine and excessive vehicle emissions from their extensive freeway system.

There are a few ways to easily distinguish photochemical smog from industrial fog.  The latter may obscure visibility whereas the former usually presents as more of a brownish orange haze.  Particular meteorological conditions foster the formation of smog.  Air inversion in which hot air presses onto the cooler air below will concentrate smog near the ground where it is more likely to cause respiratory problems.  Stagnant winds are also a factor.

Some cities will issue a ‘smog warning’ when smog has reached a particularly inhospitable level.  Children and the elderly suffer the effects most severely along with those who have compromised respiratory systems. Smog irritates mucus membranes in the eyes and nose which can lead to tenderness and discomfort.  Persistent smog has been known to cause health problems in people, animals, and plants alike.  At its most insidious, smog can have a corrosive effect on vehicles and buildings and a number of historical buildings are known to be at risk of smog corrosion.

A mixture of pollutants, principally ground-level ozone, produced by chemical reactions in the air involving smog-forming chemicals.

Smog is a type of air pollution and is a portmanteau of smoke and fog. Some smog is usually a result of coal burning. Today most smog is from vehicles and industrial emissions.