Don't "nag" him about stopping smoking. We all have done it to our parents. I lived with my mother the last 6 years of her COPD. We always wanted her to stop smoking. In the end, it'll just make you feel guilty. She had her last cigarette 30 minutes before she became inpatient at a Hospice house! He'll stop if he wants to, but as mom would say, "they've given me a death sentence, why quit now?" Chances are, your dad's been given the same crappy news (be it the end could be 10 years away). Take this time to listen to his stories. Use the last years to get those receipes you always wanted. Make sure he has his favorite dinner A LOT. This isn't about the end, it's about Truly enjoying him. Learn the things you want to learn that only he can teach you (how to change a toilet, how to fix a lawn mower, etc...). Does he have rescue inhalers? When he goes into a coughing fit, he really should have one on hand always. They'll instantly open his bronchial tubes and allow more oxygen in. Just tell him that you heard it on the radio or something and that it's small enough to fit in a pocket (so he won't feel stupid carrying one around). Keep posting here. Many of us have or have had parents with COPD. You'll need a place to vent where other people know your frustration with the illness. The stages are weird and could take YEARS (hopefully) to affect your dad. Vent, get it out. It's better to do it to strangers than to family members who will remember.
Best of luck