Chronic Obstructive Pulmonary Disease (COPD): The low FEV1/FVC ratio indicates an obstructive lung disease. Given the severity of the obstruction (FEV1/FVC 36%) and the presence of a significantly reduced FEV1 (35% of predicted), COPD is the most likely diagnosis, especially in a patient with a history of smoking or exposure to lung irritants.

Asthma: Although asthma can present with similar spirometric findings, the severity of the obstruction and the lack of mention of reversibility with bronchodilators make COPD more likely. However, asthma should be considered, especially if there are symptoms of wheezing, variable symptoms, or a known history of asthma.
Bronchiectasis: This condition can cause obstructive lung disease due to chronic inflammation and damage to the bronchi. While less common than COPD, it should be considered, especially if there's a history of recurrent infections or hemoptysis.

Cystic Fibrosis: Although rare, cystic fibrosis can cause severe obstructive lung disease and should not be missed due to its significant impact on management and prognosis. It's more likely in younger patients or those with a family history.
Alpha-1 Antitrypsin Deficiency: This genetic disorder can lead to early-onset COPD, especially in non-smokers. It's crucial to diagnose due to the potential for liver disease and the availability of specific treatments.

Obstructive Sleep Apnea (OSA) with Pulmonary Hypertension: While OSA itself does not directly cause obstructive lung disease on spirometry, associated pulmonary hypertension could lead to secondary changes. However, this would be an uncommon presentation.
Lymphangioleiomyomatosis (LAM): A rare lung disease affecting primarily women, characterized by cystic lung lesions. It can present with obstructive lung function but is much less common than COPD or asthma.