What is the difference between harmful and beneficial ozone... and how can one gas have a harmful and another beneficial effect on humans and the environment?!

Weather of Arabia - The ozone layer in the Earth's upper atmosphere protects human health, agricultural crops and ecosystems from damage caused by excessive ultraviolet radiation. But in the lower atmosphere, the scenario is different, where human activities can cause a lot of ozone, which threatens human health, crops and ecosystems, so how can one gas carry a harmful effect and another beneficial?!

Beneficial ozone (stratospheric ozone)

Ozone (O3) is a gas naturally produced in the atmosphere. Most of the ozone in the Earth's atmosphere is formed in the stratosphere, about 15 km above the Earth's surface.

The ozone here forms the ozone layer, which acts as a natural shield that protects the earth from harmful sunlight. This ozone depletion caused a lot of concern in the seventies and eighties, when scientists discovered that gases used in sprays and refrigerants, such as chlorofluorocarbons (CFCs), were It causes a huge seasonal hole in the ozone layer.

Then the world moved and countries signed the Montreal Protocol to phase out these gases, the agreement was a huge success, and now scientists are watching the ozone layer recover. This is good news for the planet, as the ozone layer prevents the risks caused by harmful rays from the sun, including: cancer and cataracts, and protects agricultural crops and ecosystems.

(Where are the beneficial stratospheric ozone and harmful tropospheric ozone located)

Harmful ozone (tropospheric ozone)

As it is said, there are two sides to the same coin, and ozone has two sides, one harmful and dangerous, and the other beneficial and necessary. How is that?!

After we got to know the beneficial ozone in the stratosphere , which forms a concentrated layer that contains 90% of the ozone in the Earth's atmosphere, ozone gas is also present in the troposphere near the Earth's surface, but in lower concentrations, and this is the harmful ozone, which constitutes 10% of the total ozone in the atmosphere.

Most of the tropospheric ozone is located at an altitude of less than 2-3 km, so it is also referred to as "surface ozone". Surface ozone is described as harmful ozone because at high concentrations it poses a threat to human health and the production of crops and natural plants, including forests.

In 2010, the Environmental Effects Assessment Panel (EEAP) reported that 1-1.25 million deaths globally can be attributed to ozone pollution of near-ground air, while long-term exposure to high levels of surface ozone may contribute to disease. Respiratory, cardiovascular, including hypertension, heart disease and stroke.

Inhaling ozone causes inflammation and damage to the airways and lungs. This can lead to problems even in people who do not have any pre-existing respiratory diseases, but it is more harmful for those who already have the disease.

The EEAP team also noted preliminary evidence that high levels of air pollution may be associated with worse health outcomes for people infected with the coronavirus (COVID-19).

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Effects of surface ozone on agricultural crops and vegetation

Many plants, from lichens to forest trees, are damaged by exposure to surface ozone. Estimates of global crop losses from soybeans, wheat, rice and maize due to surface ozone range from 4%-12%, some studies have found greater reductions in crop yields in some areas, and higher concentrations of surface ozone also harm forest growth and productivity. This reduction in growth reduces the ability of forests to absorb carbon dioxide, which contributes to the increase in carbon dioxide in the atmosphere, which is a major driver of climate change.

How is surface ozone formed?

Surface ozone is naturally formed in very low concentrations even in pollution-free air, but the presence of pollutants contributes to the production of much larger quantities, as ozone is produced by chemical reactions between a mixture of human-produced air pollutants, including nitrogen oxide (NOx) and oleander. Carbon dioxide (CO) and hydrocarbons. Higher temperatures and bright sunlight speed up these reactions, so surface ozone concentrations are usually higher in warm, sunny weather.

In general, surface ozone tends to form in greater amounts in urban areas where emissions from industry and transportation release high concentrations of nitrogen oxides and hydrocarbons, and surface ozone may then spread from urban to rural areas by wind.

Can harmful ozone be controlled?

Unlike the Montreal Protocol, which protects the beneficial ozone in the ozone layer, there is no global treaty that protects us from the harmful effects of ozone, however, many countries include surface ozone as part of air quality standards and clean air systems, in order to reduce the emission of pollutants from industry power plants and means of transportation and their regulation, and measures to reduce hydrocarbon emissions from organic solvents and incomplete combustion of vehicle fuels.

In conclusion, there is only one type of ozone, and it differs in its benefits and harms depending on where it is located, whether in the stratosphere or troposphere, it will have very different effects on humans, crops, animals and ecosystems. Therefore, it is important for the world to commit to implementing the Montreal Protocol to protect the "beneficial ozone" in the stratosphere that protects us, and to reduce the causes of surface ozone formation to protect ourselves and the environment.

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