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Zorluk: Çok zorClimate Change, Global Warming and Ozone Layer Depletion

Consider the following statements regarding the atmospheric chemistry of ozone layer depletion and polar stratospheric clouds (PSCs):

1. Type I PSCs, composed mainly of nitric acid trihydrate (HNO3⋅3H2OHNO_3 \cdot 3H_2O), form at lower temperatures than Type II PSCs, which consist of pure water ice.
2. Heterogeneous reactions on the surfaces of PSC particles convert inactive reservoir species such as chlorine nitrate (ClONO2ClONO_2) and hydrogen chloride (HClHCl) into photolytically active chlorine compounds like molecular chlorine (Cl2Cl_2).
3. In the polar springtime lower stratosphere, ozone destruction occurs predominantly through the ClOClO dimer (Cl2O2Cl_2O_2) catalytic cycle rather than the atomic oxygen-dependent cycle.

Which of the statements given above is/are correct?

  1. A
    2 only
  2. B
    1 and 2 only
  3. 2 and 3 onlyCevap
  4. D
    1, 2 and 3

Cevap

Statements 2 and 3 are correct.
Statements 2 and 3 are correct. Type I Polar Stratospheric Clouds (PSCs) form at roughly 195 K195\text{ K} (−78∘C-78^\circ\text{C}), whereas Type II PSCs require even colder conditions (below 188 K188\text{ K} or −85∘C-85^\circ\text{C}) to form pure water ice. Thus, statement 1 is incorrect. Heterogeneous reactions on PSC surfaces convert inert reservoir species (HClHCl and ClONO2ClONO_2) into active Cl2Cl_2. When sunlight returns in spring, Cl2Cl_2 photolyzes into reactive chlorine radicals, which destroy ozone predominantly via the ClOClO dimer (Cl2O2Cl_2O_2) catalytic pathway in the lower stratosphere where atomic oxygen is scarce.

Adım Adım Çözüm

1
Evaluate Statement 1 regarding PSC formation temperatures
Statement 1 is incorrect because Type I PSCs (nitric acid trihydrate) condense at higher temperatures (~195 K) than Type II PSCs (pure water ice, forming below ~188 K).
Water requires colder temperatures to freeze into ice particles than nitric acid trihydrate requires to crystallize.
2
Evaluate Statement 2 regarding heterogeneous surface reactions
Statement 2 is correct. PSC surfaces provide ice crystals for inactive reservoir chlorine molecules (HClHCl and ClONO2ClONO_2) to react, forming Cl2Cl_2 gas.
During the polar night, these heterogeneous reactions convert stable reservoir species into photolytically unstable molecular chlorine.
3
Evaluate Statement 3 regarding polar ozone destruction pathways
Statement 3 is correct. Because atomic oxygen (OO) is extremely scarce in the lower stratosphere during early spring, the ClOClO dimer (Cl2O2Cl_2O_2) catalytic cycle accounts for over 75% of Antarctic ozone loss.
The dimer Cl2O2Cl_2O_2 photolyzes under sunlight into ClOOClOO and ClCl, freeing chlorine atoms to destroy ozone without requiring free atomic oxygen.

Anahtar Kavram

Heterogeneous stratospheric chemistry and PSC-driven polar ozone depletion catalytic cycles
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Konular

Climate Change, Global Warming and Ozone Layer Depletion