A 68-year-old male ex-smoker presents with a 6-month history of progressive exertional dyspnea and dry cough. On examination, bibasilar fine end-inspiratory crackles are heard. High-resolution CT chest shows a subpleural, basilar predominant reticular pattern with honeycombing and traction bronchiectasis consistent with usual interstitial pneumonia (UIP). Pulmonary function testing shows the spirometric pattern marked **A** in the diagram. Which of the following best explains the pathophysiology of this patient's lung disease?