Flash writing 11/4

The trees had started to turn the colors of autumn. Not all at once but from the top, like a green candle kisssed with flame. Reds and oranges wrapping the glistening branches in festive finery.
The bus was full as it slowly climbed the west hills. People wrapped in scarves, coats, gloves and the warm relief of coffee crowded close for lack of space and warmth.
Not everyone heard it a the same time. A siren from somewhere in the fog of morning approached. As it grew louder people started tugging off headphones, looking around for the noise.
Morning chatter fell silent.
The driver pulled the bus to the side a grim look on her face.
The red fire truck slowed as it went through the intersection.
The people were quiet as it passed, not wanting to draw the attention of such a predator.
Is this fog, or smoke?