Identifying Peaceful Diction

Read the following excerpt from a piece of prose:

"As the morning light filtered through the curtains, illuminating the dust motes swirling lazily in the air, Jane sat at her desk, contemplating the day's tasks with a sense of calm anticipation. The soft chirping of birds outside blended with the faint rustle of leaves, creating a serene backdrop to her thoughts."

In the excerpt, which word most contributes to the overall peaceful tone of the passage?