Which literary technique does shelley employ by addressing the west wind at the beginning and throughout the ode?

The answer is apostrophe. "Ode to the West Wind" poem, written by Percy Bysshe Shelley in 1819, published in 1820. In order to address the west wind directly shelly used apostrophe in  “Ode to the West Wind”. In this poem Shelly addressed the west wind directly and calling it “thu” which is an example of apostrophe.

in that passage i would say the sentence which best describes the overall impact of the setting is when they mention the absence of people because it suggests that taking a walk at night is unusual.

this answer was editing it cause i couldn't delete!