Smog and its impact

Smog is a mixture of air pollutants—nitrogen oxides and volatile organic compounds—that combine with sunlight to form ozone. Smog is a yellowish or blackish fog formed mainly by a mixture of pollutants in the atmosphere which consists of fine particles and ground level ozone.

Hence the term “smog” describes a mixture of emissions under specific climate conditions.

How Smog is Formed?

The atmospheric pollutants or gases that form smog are released in the air when fuels are burnt. When sunlight and its heat react with these gases and fine particles in the atmosphere, smog is formed. It is purely caused by air pollution. Ground level ozone and fine particles are released in the air due to complex photochemical reactions between volatile organic compounds (VOC), sulphur dioxide (SO2) and nitrogen oxides (NOx). These VOC, SO2 and NOx are called precursors. The main sources of these precursors are pollutants released directly into the air by gasoline and diesel-run vehicles, industrial plants and activities, and heating due to human activities.

Waste incinerators, burning of coal and vehicular and industrial emissions are the main gasses that form smog when acted upon by the sun’s ultraviolet light together with particulate matter and volatile organic compounds. Dense urban areas suffer more from smog because of huge numbers of traffic, industries, and combustion of different types of fuel. Smog has serious negative effects on people, plants, and animals.

Health Effects

Ground-level ozone, sulfur dioxide, nitrogen dioxide and carbon monoxide are especially harmful for senior citizens, children, and people with heart and lung conditions such as emphysema, bronchitis, and asthma.

It can inflame breathing passages, decrease the lungs working capacity, cause shortness of breath, pain when inhaling deeply, wheezing, and coughing.

It can cause eye and nose irritation and it dries out the protective membranes of the nose and throat and interferes with the body's ability to fight infection, increasing susceptibility to illness. Hospital admissions and respiratory deaths often increase during periods when ozone levels are high.

Practice question:

1. Which of the following statement related to photochemical smog is correct?

a) Photochemical smog is due to the high concentration of sulfur oxides in the air.

b) It occurs in the region in which air contains high liquid water contents.

c) Photochemical smog forms as a result of interactions among nitrogen oxides, reactive hydrocarbons
and sunlight.

d) None of the above

Ans: c
Exp: Sulfurous smog results from a high concentration of sulfur oxides in the air and is caused by the use of sulfur-bearing fossil fuels, particularly coal. Photochemical smog, which occurs most prominently in urban areas that have large numbers of automobiles, requires neither smoke nor fog. This type of smog has its origin in the nitrogen oxides and hydrocarbon vapors emitted by automobiles and other sources, which then undergo photochemical reactions in the lower atmosphere.