left hypertensive pneumothorax with bi-lobar atelectasia of the left lung in a young subject (I suppose ...)
Left pleural effusion is quite possible but it usually has contra lateral deviation of trachea. Underlying etiology could be pneumonia. Lobar pneumonia may not necessarily not have patchy infiltrates but the x ray looks more like that of pleural effusion and underlying etiology could be pneumonia
Lt sided pleural effusion, mostly due to severe pneumonia involving the Lt lower lobe..the effusion is mostly an empyema !