The word smog or smoky fog as it is described is not just a trouble to vision but also very deadly. Smog gets formed due to air pollution. Air gets polluted in various ways, the major contributor being our means of transportation. Others include burning of garbage, factories, tanneries, power plants and natural disasters like volcanic eruption. All these activities release carbon dioxide, carbon monoxide, hydrocarbons, nitrogen oxide, sulphur based compound into the atmosphere. Smog is caused by the photo-chemical reaction of a mixture of man-made pollutants, heat and sunlight.
When the two common air pollutants hydrocarbons and nitrogen oxide come together, a chemical reaction occurs due to Sunlight. The result of this reaction produces a compound called ozone (O3) which is the most important ingredient of smog. Ozone as we know will do go good only if it is present in the stratosphere where it gets produced to absorb harmful UV radiations. But at the ground level, this ozone is dangerous. In the presence of oxygen and sunlight, the nitric oxides combine with organic compounds, such as the hydrocarbons from unburned gasoline, to produce a whitish haze.
Smog results in general respiratory problems such as wheezing and shortness of breath, as well as nausea and headaches. Repeated exposure can even cause irreversible lung damage and increase the risk of lung cancer. The severity of smog in urban cities can be measured from the levels of ground level ozone. As a result of heat from the rays of the sun, the concentration of ground-level ozone is highest in urban centers in the summer.
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