Sort each reaction by where it occurs and what it produces, rather than reasoning through the full mechanism each time. Ask two questions per option: (1) does the reaction occur in the troposphere involving NOx, hydrocarbons, and O3, or does it belong to the stratosphere involving CFCs and ozone layer chemistry? (2) does the product list include a species characteristic of smog, namely $O_3$, regenerated $NO_2$, or an oxidation product like $HCHO$?
For (A): $CFCl_3 + h\nu \rightarrow CFCl_2 + Cl\cdot$, the reactant is a CFC, and CFC photolysis by high energy UV is the signature first step of stratospheric ozone depletion. It fails test (1). Exclude.
For (B): $CH_3O_2 + NO + O_2 \rightarrow HCHO + HO_2 + NO_2$, a peroxy radical converts $NO$ to $NO_2$ while yielding $HCHO$, a classic tropospheric VOC oxidation footprint. Passes both tests. Include.
For (C): $NO_2 + O_2 + h\nu \xrightarrow{M} O_3 + NO$, directly produces $O_3$ from $NO_2$ photolysis, the literal ozone forming step of smog. Passes both tests. Include.
For (D): $CH_4 + 8O_2 \rightarrow CO + H_2O + 2OH\cdot + 4O_3$, a net equation yielding $4O_3$ molecules, an aggregate smog chain outcome from a single hydrocarbon. Passes both tests. Include.
Collecting the reactions that pass:
\[ \{B, C, D\} \subset \text{tropospheric smog reactions}, \quad A \in \text{stratospheric ozone depletion} \]
\[\boxed{\text{Answer: (B), (C), (D)}}\]