Usually the urban atmosphere is invisible. Periodically it becomes visible. This happens in spring and in autumn. In spring the petals of the fruit trees fall and are blown by the wind. In autumn the leaves fall. In quiet corners they overwinter and can last far into spring.
But the best wind indicator is the fruit of the elm tree. Light and numerous - just like natural confetti. These little "coins" reveal the lightest eddies and dust devils.
Notice how the individual particles move over long distances, but how the large-scale pattern stays constant.
Elm tree - Wikipedia
Dust_devil - Wikipedia
Eddy - fluid dynamics - Wikipedia