* A sense of peace and joy: The poem is filled with descriptions of nature, including "the sweet breeze" and "the soft green trees." These elements evoke a feeling of serenity and contentment. The "blessing in the air" could represent this overall sense of peace and joy that permeates the environment.
* The beauty of nature: Wordsworth was a Romantic poet deeply connected to nature. The "blessing" could refer to the beauty and wonder he finds in the natural world, a beauty that inspires him and brings him happiness.
* A connection to something greater: The "blessing" could also symbolize a sense of divine presence or spiritual connection. It could be a way of describing the feeling of being part of something larger than oneself, a feeling often associated with experiencing nature.
* A shared experience: The poem is addressed to Wordsworth's sister, and the "blessing" could refer to the joy and happiness they share as siblings. It could be a way of describing their special connection and the sense of companionship they feel in nature.
Ultimately, the meaning of "blessing in the air" is open to individual interpretation. However, it is likely that it refers to a positive and uplifting emotion associated with nature, beauty, and perhaps even a deeper sense of connection.