Question

Identify a deadly poisonous gas X found at the higher levels of the atmosphere. Write its chemical formula and equation of its formation. Why is damage to X layer a cause of concern?

Answer 1

Hint: Ozone (${O}_{3}$) is a highly reactive gas. It is both a natural and a man-made product that occurs in the Earth's upper atmosphere: (the stratosphere) and lower atmosphere (the troposphere). Depending on its position in the atmosphere, ozone affects life on Earth in either good or bad ways.

Complete Answer:
The deadly poisonous gas found at the higher levels of atmosphere is the ozone gas. The ozone layer or ozone shield is a region of Earth's stratosphere which absorbs most of the Sun's ultraviolet radiation. It contains less than 10 parts per million of ozone, while the average ozone concentration in Earth's atmosphere as a whole is about 0.3 parts per million. The ozone layer is mainly found in the lower portion of the stratosphere, from approximately 15 to 35 kilometres (9 to 22 mi) above Earth. Its thickness varies seasonally and geographically. The sun’s measurements showed that the radiation sent out from its surface and reaching the ground on Earth is usually consistent with the spectrum of a black body with a temperature in the range of 5,500–6,000 K (5,230–5,730 °C), except that there was no radiation below a wavelength of about 310 nm at the ultraviolet end of the spectrum. It was concluded that the missing radiation was being absorbed by something present in the atmosphere. Eventually, the spectrum of the missing radiation was matched to only one known chemical, ozone.
Formula: ${O}_{3}$
An oxygen molecule is split (i.e., photolyzed) by higher frequency UV light into two oxygen atoms: ${O}_{2} + {ℎν} → {2}{O}$. Each oxygen atom quickly combines with an oxygen molecule to form an ozone molecule: ${O} + {O}_{2} → {O}$.
In 1976, atmospheric research revealed that the ozone layer was being depleted by chemicals released by the industries, mainly chlorofluorocarbons (CFCs). Concerns that the increased UV radiation due to ozone layer depletion threatened life on Earth, including increased skin cancer in humans and other ecological problems. It led to bans on the chemicals and other stringent measures. The depletion of the ozone layer exposes the Earth’s surface to dangerous levels of UV rays.

Note:
The word "ozone" means smelly in Greek because of the gas’s strong odour. The CFC molecules are highly stable and can last for up to 100 years. One chlorine molecule from a CFC can destroy up to 100,000 ozone molecules.