Question

In Antarctica, ozone depletion is due to the formation of which of the following compounds? (a) Acrolein (b) PAN (c) PCBs (d) Chlorine nitrate

Short answer

The formation of chlorine nitrate contributes to ozone depletion in Antarctica.

Step-by-step solution

Understanding Ozone Depletion

Ozone depletion primarily refers to the thinning of the ozone layer in the stratosphere. It is caused by the presence of certain chemicals that contain chlorine or bromine. These chemicals are called ozone-depleting substances (ODS).

Identifying the Compound

Among the given options, the compound that contains chlorine and is known to contribute to ozone depletion in Antarctica is chlorine nitrate. Chlorine nitrate forms from the reaction of chlorine and nitrogen dioxide, which are released from man-made compounds such as chlorofluorocarbons (CFCs).

Eliminating Incorrect Options

Acrolein, PAN (Peroxyacetyl nitrate), and PCBs (Polychlorinated biphenyls) are not directly involved in the chemical reactions that lead to the depletion of the ozone layer. They do not release chlorine or bromine atoms which can catalyze the breakdown of ozone.

Key concepts

Chlorine Nitrate

Chlorine nitrate is a key player in the complex set of reactions leading to ozone depletion, particularly in the polar stratosphere. It forms through the reaction between chlorine monoxide (ClO) and nitrogen dioxide (NO₂). Chlorine nitrate acts as a reservoir for chlorine atoms, which, under certain conditions, can be liberated to participate in ozone destruction. The polar winter and the presence of polar stratospheric clouds provide the right environment for these chlorine atoms to become active in depleting the ozone layer. With the arrival of sunlight in the polar spring, these molecules are broken down, releasing chlorine atoms that catalytically destroy ozone molecules. Understanding the role of chlorine nitrate and its interactions in the stratosphere is essential for grasping why it's identified as the culprit in ozone layer depletion in regions like Antarctica.

Ozone-Depleting Substances (ODS)

Ozone-Depleting Substances (ODS) are compounds that have the potential to reach the stratosphere and release chlorine or bromine atoms upon exposure to ultraviolet (UV) light. These substances include chlorofluorocarbons (CFCs), halons, carbon tetrachloride, and methyl chloroform. Once in the stratosphere, these atoms participate in chemical cycles that lead to the breakdown of ozone (O₃), thus thinning the protective ozone layer. Because of the long atmospheric lifetimes of these substances, they can cause damage for many years after their release. The identification and phasing out of ODS through international efforts like the Montreal Protocol have been vital in mitigating further harm to the ozone layer.

Chlorofluorocarbons (CFCs)

Chlorofluorocarbons (CFCs) are a class of chemicals primarily used in the past as refrigerants, propellants in aerosol sprays, and in foam blowing. These human-made substances have been heavily implicated in ozone layer depletion. When CFCs reach the stratosphere, they are eventually broken down by UV radiation, releasing chlorine atoms that participate in ozone depletion cycles. A single chlorine atom from a CFC molecule can destroy thousands of ozone molecules before being neutralized. This high ozone-depletion potential, combined with the longevity of CFCs in the atmosphere, prompted the global community to drastically reduce their production and use under the Montreal Protocol.

Stratospheric Chemistry

Stratospheric chemistry involves the study of chemical interactions occurring in the Earth's stratosphere, the second major layer of the atmosphere. This field is crucial for understanding phenomena like ozone layer depletion. In the stratosphere, solar radiation drives chemical reactions involving natural and man-made substances. The famous ozone layer, situated within this realm, is both created and destroyed by these chemical processes. Stratospheric ozone is vital for life on Earth because it absorbs most of the Sun's harmful UV radiation. Unraveling the complex chain of reactions in this atmosphere layer, which involve chlorine and bromine from ODS, continues to be a core task for atmospheric chemists seeking to protect our environment.