O ozônio na estratosfera

Neusa Paes Leme,Plínio Alvalá

Ozone in the stratosphere has a very particular chemical, acting as a sunscreen , blocking harmful UV radiation to living beings. For this reason it is known as ozone "good" . It is capable of absorbing about 90% of UV-B radiation , 10% of UV-A and 100% of UV-C (totally absorbed from the atmosphere at the top).

Figure 2 - Illustrates the absorption of UV radiation by the ozone layer.
Source: adapted figure www.nasa.gov

Temperature profiles and stratospheric chemistry are directly related to the presence and production processes and ozone loss in this layer. These processes were first described by Chapman in 1930, and involved a closed cycle with the reactions below: hυ → O2 + O + O (1) hυ is solar UV radiation <240 nm

O + O2 + M → O3 + M (2)
M is a third chemical that acts as a catalyst in the reaction, for example, NO2 or other O2. O + O3 → 2O2 (3) O3 + O + O2 → hυ (4) Later it was found that there were other reactions that destroy ozone in the stratosphere, mainly by catalytic cycles involving free radicals such as nitrous oxide (N2O), chlorine (Cl), bromine (Br), which are retained in the process destroying many ozone molecules before being removed. Figure 3 shows a schematic of the catalytic ozone destruction by chlorine radical.

Figure 3 - Scheme of ozone destruction by chlorine in the stratosphere.
Source: www.nasa.gov