Some scientists have predicted that a global nuclear war on the earth would be followed by a severe nuclear winter with a devastating effect on life on earth. What might be the basis of their prediction ?

Question

$\begin{array}{1 1} \text{Formation of charged particles after the nuclear war } \\ \text{Formation of clouds after the nuclear } \\ \text{Formation of dust particles after the nuclear war} \\ \text{Formation of water particles resulting in ice and show after a nuclear war} \end{array}$