The Stratosphere & Ozone (O₃)

Effect of UV radiation in humans

skin cancer

sunburn

premature aging of skin

Effect of UV radiation on other biodiversity

animal - skin cancer in animals

marine - plankton population threatened

plants - crop species impacted by lower growth

Ozone

is formed through a photochemical reaction, much less stable than oxygen and is very reactive

Ozone formation

creation: an oxygen molecule is split by a photon of light ( higher frequency UV light) into 2 oxygen atoms, the atomic oxygen produced quickly reacts with another oxygen molecule to reform ozone

destruction: if an oxygen and an ozone molecule meet,they recombine to form 2 oxygen molecules

Disadvantages of Chapman cycle

it predicts too much ozone as it doesn’t take into account for sinks, pathways that destroy ozone (oxide family)

Sources of oxide family

NOx - natural sources mainly also from fertilizer application

HOx - natural sources mainly also from agri application

ClOx & BrOx - nearly entirely due to human activity (CFC’s)

CFC’s (chlorofluorocarbons)

unreactive in the troposphere and moves unchanged to the stratosphere

Destruction of O₃ by CFC’s

short wave UV light in stratosphere breaks down CFC’s and chlorine is released,

Cl + O3→ ClO + O2 (step 1)

ClO+O.→Cl+O2 (step 2)

O3+O.→2O2 (overall rxn)

Ozone Depleting Potential (ODP)

the ODP is the ratio of the impact on ozone of a chemical compared to the impact of a similar mass of CFC-11