Smog Is A Result Of Excessive Air Pollution.
The mix of smoke and fog is known as smog. It is a result of excessive air pollution. The term smog was first used in the year the 1900s. There are mainly two types of smog.
- Photochemical smog
- Sulfurous smog
Smog is mainly caused by nitrogen dioxides, sulfur oxide, smoke, coal combustion, vehicular emissions, forest and agricultural fire and other particulates combined with moisture in the air. What we see primarily is photochemical smog.
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On the 5th of December 1952, sulfurous smog was first observed in London. It developed, due to the high concentration of sulfur in the air. A great air polluting substance that comes from sulfur-bearing fossil fuels like coal and volcanoes which also emit sulfur dioxide in the atmosphere. This affected mainly the eyes and lungs and caused 4000 respiratory deaths. It is formed in the mornings of winter when the temperature is low. Countries like China, Mexico and Poland experience a high level of photochemical smog. The government tried many methods to tackle it, from reducing the number of cars, to checking the health of vehicles, to considering the use of gas instead of wood etc.
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- Volatile organic compounds, or VOCs
- Nitrogen oxides.
VOCs are compounds that easily become vapors and may contain elements, such as carbon, oxygen, hydrogen, chlorine and sulfur. Some are naturally produced by plants and animals but others come from manmade sources, like solvents, paints, glues, and petroleum. Meanwhile, the incomplete combustion of gas in motor vehicles releases nitrogen oxide. That's what gives this type of smog its yellowish color. VOCs and nitrogen oxide react with sunlight to produce secondary pollutants called PANs and tropospheric or ground-level ozone.
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Smog isn't just an aesthetic eyesore. Both forms of smog irritate the eyes, nose, and throat. Exacerbate conditions like asthma and emphysema, and increase the risk of respiratory infections like bronchitis. Smog can be especially harmful to young children and older people and exposure in pregnant women has been linked to low birth weight and potential birth defects. Secondary pollutants found in photochemical smog can damage and weaken crops and decrease yield, making them more susceptible to insects. As the result the Clean Air Act of 1956 banned burning coal in certain areas of the city, leading to a massive reduction in smog. Similarly, regulations on vehicle emissions and gas content in the US reduced the volatile compounds in the air and smog levels along with them.
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Classical smog is produced by the combustion or burning at fossil fuels like coal, petrol or gasoline and caused by a mixture of smoke and sulfur dioxide present in air. Classical smog also known as London smog. It occurs in cool, humid climate. Major constituents are smoke, fog and sulfur dioxide. it can occur both during the day and at night. In December 1952, London was trapped in the deadly cloud of fog and pollution for five days. At that time, the city ran on cheap coal for everything, from generating power to heating homes which was the result of classical smog.
In the reaction of photochemical smog, at first nitrogen and oxygen combine in the combustion process to form nitric oxide. Then this nitric oxide, oxidized in the atmosphere to produce nitrogen dioxide. Next sunlight breaks down nitrogen dioxide into nitric oxide and an oxygen radical. The oxygen radical combines with molecular oxygen to form ozone. Ozone is the main component of photochemical smog. Nitric oxide can remove ozone by reacting with it to form nitrogen dioxide and oxygen. Nitric oxide and nitrogen dioxide can also react with the hydrocarbons instead of ozone to form other volatile compounds known as PANs, It means a nitrate reacted hydrocarbon from out of exhaust interact with ozone to from the hydrocarbon free radical . This hydrocarbon free radical rapidly reacts with oxygen to from another hydrocarbon free radical. Then the free radical reacts with nitric oxide to produce nitrogen dioxide and the free radical hydrocarbon. This new free radical next interacts with oxygen to yields is stable aldehyde and hydro peroxide radical. Hydro peroxide a de coal then reactive with another molecule of nitric oxide to give nitrogen dioxide and hydrogen radicals. The hydro peroxide a de coal is extremely reactive and rapidly reacts with a stable hydro carbon to yield water and regenerate the hydro carbon free radical. Thereby completing cycle.
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