Have you noticed when you drive into a big city that from a distance the skyscrapers seem to be surrounded by a grayish/brown haze? Or if you have flown in an airplane, have you noticed the sky around a city from a distance?


That haze is smog. Smog is a combination of the words smoke and fog and is used to describe heavily polluted air. Almost every big city in the world has smog. Does this give you any clues as to the cause?


Large industrial cities such as Houston, New York and Los Angeles contain highly polluted atmospheres.
The cause of the pollution is the formation of the compound known as ozone (O3). Ozone in the upper atmosphere is actually healthy because it absorbs the harmful rays of the sun.

However, ozone formed at ground level can cause harm to our health. Ground-level ozone contributes to the creation of smog

Ten to 30 miles above the earth is a layer of ozone that absorbs ultraviolet light from the sun and reduces the amount hitting the earth.

Source: New York State Dept. Environmental Conservation

Ground-level ozone forms when pollutants such as nitrogen oxide, sulfur dioxide, volatile organic compounds and particulate matter react with sunlight. Common sources of these  pollutants include:

Why Smog Matters

High levels of ground-level ozone cause the greatest health risk to the respiratory system. The ozone and other chemicals in smog irritate the eyes, throat, and lungs. Every time air is inhaled, small particles contained in the air become trapped inside the lungs. Air with high levels of ground-level ozone contains harmful particles. Constantly breathing in these harmful particles will decrease the efficiency of the lungs over time and may eventually lead to an upper respiratory infection. People with asthma are especially vulnerable.

Ground-level ozone also causes environmental problems. It inhibits the ability of plants to produce and store food, which makes them more susceptible to disease. In addition, it can reduce agricultural yields for crops that include soybeans, kidney beans, wheat, and cotton. Ground-level ozone also impacts ecosystems by disrupting water movement and exchange cycles. This adversely affects the habitats of both plants and animals.

Click here for more information about ozone.



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