How does lower pressure affect the ratio of nitrogen dioxide monomers to dinitrogen tetroxide dimers?

In the context of chemical equilibrium, the ratio of nitrogen dioxide ($N{O}_2$) monomers to dinitrogen tetroxide ($N_2{O}_4$) dimers is directly influenced by external pressure due to the change in the number of molecules during the dissociation reaction:

$$2N{O}_2\rightleftharpoons N_2{O}_4$$

Because the dissociation of one $N_2{O}_4$ dimer into two $N{O}_2$ monomers results in an increase in the total number of gas molecules, the system is sensitive to pressure changes. When the external pressure is reduced, the system shifts its equilibrium to favor the formation of more molecules to occupy a larger volume. Consequently, lower pressure shifts the equilibrium in favor of nitrogen dioxide monomers, thereby increasing the ratio of monomers to dimers.1

This process is a fundamental example of chemical relaxation, where the system requires a finite amount of time to reach a new equilibrium concentration following a change in conditions.1