The secondary precursors of photochemical smog are

How is the troposphere damaged by oxides of carbon?

$BOD$ values (in $ppm$) for clean water $(A)$ and polluted water $(B)$ are expected respectively:

Fill in the blanks:
$(1)$ $A$ special cloud is formed over the Antarctica region in winter,which is called ..............
$(2)$ $A$ known source of pollution is called ..............
$(3)$ An unknown source of pollution is called ..............
$(4)$ The concentration of dissolved oxygen in water is ......... and the concentration of dissolved oxygen in air is ............

Which gas is released when chlorine free radicals react with ozone?

What are the reactions involved in the ozone layer depletion in the stratosphere?