Question

Which of the following statements regarding ozone is correct
(a) "good ozone" is formed in the lower atmosphere (troposphere) that absorbs harmful ultraviolet rays coming from the sun. "bad ozone" is present in the upper part of the atmosphere (stratosphere) that harms plants and animals.
(b) The thickness of the ozone in an air column of air from the ground to the top atmosphere is measured in terms of Dobson units (DU)
(c) Recognizing the deleterious effects of ozone depletion, an international treaty, known as the Montreal Protocol, was signed at Montreal (Canada) in 1987 (became effective in 1989) to control the emissions of ozone depletion substances.
(d) None of these

Answer 1

Bad ozone is formed in the lower atmosphere. The 300DU ozone in the atmosphere is the thickness in the air column from top to the ground atmosphere.
Montreal protocol which was signed in 1987 became effective after two years.

Complete step by step answer:
Ozone-depleting substances, when released into the atmosphere, damage the stratospheric ozone layer which is the earth's protective shield that protects humans and the environment from the harmful UV radiation of the sun. Understanding the deleterious effects of depletion of ozone, an international treaty known as the Montreal Protocol was signed in 1987 in Montreal. This protocol became effective in 1989 to control the emission of Pollutants or substances responsible for ozone depletion.
So the correct answer is ‘Recognizing the deleterious effects of ozone depletion, an international treaty, known as the Montreal Protocol, was signed at Montreal (Canada) in 1987 (became effective in 1989) to control the emissions of ozone depletion substances'.

Additional information:
- Ozone formed in the lower atmosphere i.e, the troposphere is known as 'bad ozone' which harms plants and animals. Ozone found in the upper part of the atmosphere called the stratosphere is known as bad ozone which acts as an efficient shield by absorbing ultraviolet radiation from the sun.
- The thickness of the ozone in air column of air from the top to the ground atmosphere is measured in terms of Dobson units (DU).A Dobson unit is the number of molecules of ozone required to create a layer of pure ozone 0.01 millimeters thick at a temperature of 0 degrees Celsius and a 1 atmospheric pressure. The ozone in the atmosphere is about 300 Dobson units.
- Montreal protocol was adopted on 15th September 1987. This protocol phases down the consumption and production of the different ozone- depleting substances. This protocol differentiated equal responsibilities for both developed and developing countries for reducing the CFCs and other depleting chemicals.

Note:
The Montreal Protocol includes:
Article 2: provisions related to Control Measures article 3: Calculation of control levels
Article 4: Control of trade with non-Parties
Article 5: Special situation of developing countries
Article7: Reporting of data
Article 8: Non-compliance
Article 10: Technical assistance.