Particles having a tap density less than about 0.4 g/cm3 are formed by spray drying from a colloidal solution including a carboxylic acid or salt thereof, a phospholipid, a divalent salt and a solvent such as an aqueous-organic solvent. The colloidal solution can also include a therapeutic, prophylactic or diagnostic agent. Preferred carboxylic acids include at least two carboxyl groups. Preferred phospholipids include phosphatidylcholines, phosphatidylethanolamines, phosphatidylglycerols, phophstidylserines, phosphatidylinositols and combinations thereof. The particles are suitable for pulmonary delivery.