Solution: OH Radicals and Hydrogen Atom Generation

The question asks to identify the species that reacts with hydroxyl (OH) radicals to produce a hydrogen atom (H).

Analyzing Reactivity with OH Radicals

We need to examine the reaction products of OH radicals with each given species:

• Option 1: $CH_4$ (Methane)
  The reaction is: $OH + CH_4 \rightarrow H_2O + CH_3$. This reaction abstracts a hydrogen atom from methane, forming a methyl radical ($CH_3$), not a free hydrogen atom.
• Option 2: $NH_3$ (Ammonia)
  The reaction is: $OH + NH_3 \rightarrow H_2O + NH_2$. This reaction abstracts a hydrogen atom from ammonia, forming an amide radical ($NH_2$), not a free hydrogen atom.
• Option 3: CO (Carbon Monoxide)
  The reaction involving CO is typically: $OH + CO \rightarrow CO_2 + H$. In this reaction, a hydrogen atom (H) is generated as a product. While another common reaction pathway in the atmosphere is $OH + CO \rightarrow HO_2$, the pathway producing H is relevant here.
• Option 4: $NO_2$ (Nitrogen Dioxide)
  The reaction is: $OH + NO_2 \rightarrow HNO_3$. This is an addition reaction forming nitric acid, and it does not produce a hydrogen atom.

Conclusion

Based on the analysis of the reaction pathways, carbon monoxide (CO) is the species among the options that reacts with OH radicals to generate a hydrogen atom (H).

Correct Answer: Option C (CO)