The simplest way to see impressionistic writing is relating to the character's environment through the character's five senses rather than narrative, omniscient description. The world is the character's impression, not the narrator's description. So the environment becomes the character's reality, not a narrator's cage for the character.
This actually reads better in nonfiction narrative. With skillful interviewing, a writer can learn how a "character" interacts with his or her world through the filter of senses shaped by a lifetime of experience.
For example hold a cup of coffee and what do you see, smell, taste, hear, feel, and how does it affect your alertness, your mood, your ability to receive information from your senses.
Simple? A central African culture (which I don't recall) has 16 names for a cup of liquid based on its purpose. They translate loosely to, a warming, a cooling, satisfier, or if you plan to throw it on someone, a word that means an instrument of annoyance. It's still the same cup and the same liquid.
I hope that helps. --HJ, St. Louis