When the popping of fireworks stops, everything suddenly goes quiet. The lingering smell of gunpowder somehow made me feel sentimental.
Literal
Fireworks [possessive-の] bursting sound [subject-が] cease-[automatic-と], suddenly surroundings [subject-が] quiet become. After [in-に] remained gunpowder [possessive-の] smell [subject-が], somehow me [object-を] sentimental mood [to-に] made.
Beautifully atmospheric writing. The ~と conditional is the 'automatic consequence' type — when the sound stops, silence naturally follows. 火薬の匂い ('smell of gunpowder') is a powerfully specific sensory detail that grounds the sentimentality in physical experience. なんだか ('somehow') marks the speaker's inability to fully explain the emotion. The shift from objective observation to subjective feeling across the two sentences is well-crafted narration.