Chronic Obstructive Pulmonary Disease (COPD): This is the most likely diagnosis given the patient's history of heavy smoking and the presence of hyperaerated lungs on the chest X-ray. COPD is a progressive lung disease characterized by airflow obstruction, primarily caused by smoking.

Asthma: Although less likely than COPD in a heavy smoker, asthma can also present with hyperaerated lungs due to air trapping. The diagnosis would depend on the presence of reversible airflow obstruction and symptoms such as wheezing, cough, and shortness of breath.
Pneumothorax: A spontaneous pneumothorax could cause hyperaerated lungs and is more common in tall, thin males, and smokers. However, it would typically present acutely with chest pain and shortness of breath.
Bullous Lung Disease: This condition involves the formation of bullae (air-filled cysts) in the lungs, which can lead to hyperaeration. It is more common in smokers.

Lung Cancer: Although less likely to cause diffuse hyperaeration, lung cancer is a critical diagnosis to consider in any smoker, especially if there are other symptoms such as weight loss, cough, or hemoptysis.
Pulmonary Embolism: While not directly causing hyperaerated lungs, pulmonary embolism is a life-threatening condition that can occur in anyone, including smokers, and requires prompt diagnosis and treatment.
Tuberculosis: In endemic areas or in individuals with risk factors, tuberculosis (TB) can present with a variety of pulmonary findings, including hyperaeration in some cases, especially if there is associated bronchiectasis or cystic changes.

Lymphangioleiomyomatosis (LAM): A rare lung disease that primarily affects women, characterized by the growth of smooth muscle-like cells in the lungs, leading to cystic changes and hyperaeration. It's less likely in a male patient but should be considered in the differential for hyperaerated lungs.
Cystic Fibrosis: Typically diagnosed in childhood, cystic fibrosis can lead to bronchiectasis and hyperaeration. However, it would be extremely rare for this diagnosis to be made for the first time in a 36-year-old without a previous diagnosis or suggestive symptoms.
Alpha-1 Antitrypsin Deficiency: A genetic disorder that can lead to COPD-like symptoms and hyperaeration in the lungs, even in non-smokers or light smokers. It's an important consideration in younger patients with lung disease.