When atmospheric oxygen influenced by UV rays in stratosphere it decomposes into two nascent oxygen atoms. The nascent thus formed combines with O2 to form ozone.
\(O_2+O\xrightarrow{UV\;rays}O+O\)
\(O_2+O\xrightarrow{UV\;rays}O_3\)
Similarly, When ozone absorbs low wavelength UV rays, They dissociate into oxygen and nascent oxygen and finally nascent oxygen forms oxygen molecule.
\(O_3+O\xrightarrow{UV\;rays}O_2+O\)
\(O+O\xrightarrow{UV\;rays}O_2\)
In this way there is continuous formation and decomposition of ozone. Thus it balances the thickness of ozonosphere.