Hydrolyzes specifically phosphatidic acid (PA) to produce 2- acyl lysophosphatidic acid (LPA; a potent bioactive lipid mediator) and fatty acid. Does not hydrolyze other phospholipids, like phosphatidylserine (PS), phosphatidylcholine (PC) and phosphatidylethanolamine (PE) or triacylglycerol (TG). . This is the function of LIPI (lipase I, ENSG00000188992).