Why is the air smoke less in poem sonnet composed upon Westminster bridge?

In the poem "Composed upon Westminster Bridge" by William Wordsworth, the speaker describes a moment in the early morning when the city is still and the air is clear. The lack of smoke in the air could be attributed to the time of day and the absence of heavy industrial activity, allowing for a more tranquil and pristine scene. Wordsworth emphasizes the beauty of the cityscape untouched by the pollution that typically obscures its features.