Exposure to welding fumes has been linked to a multitude of respiratory health problems, chronic pulmonary disease and cancer. The lungs are constantly exposed to the outside environment through our breathing. The respiratory tract lining fluid coats the distal airways where gas exchange occur is known as the silent zone of the lungs. It is here the welding fumes deposit in the small airways where the lining fluid acts as the first line of defense. The lining fluid is composed of bioactive phospholipids and proteins, and the need to understand lipid and protein dysregulation and interactions in pathogenesis is key. Our study aims to investigate alterations in phospholipid and protein composition of the small airway lining fluid and its association with pulmonary function among welding fume-exposed workers. Deploying the innovative technique of Particles in Exhaled Air (PExA), we collected small airway lining fluid from 134 subjects, of which 55 were exposed in welding industry. Analysis of the samples were conducted by means of tandem mass spectrometry. A subset of samples of the welding fume exposed lining fluid where sent to SomaLogic for protein analysis through the SomaScan platform. The subjects were also examined with pulmonary function tests including: spirometry, diffusing capacity of carbon monoxide (DLCO), while small airway function was assessed using impulse oscillometry (IOS) and multiple breath washout (MBW), and blood sampling. We will use a combination of machine learning and statistical analysis to associate molecular profiles (lipids and proteins) to welding fume exposure as well as to pulmonary function.