Intraalveolar pressure is 0. Positive IPP would collapse the lung. Just like if you were to fill an air balloon with RA then put it under positive pressure.
Two ways to keep alveoli open, one is to increase positive alveolar pressure ( via gas) or two, increase the negative pressure in the intra pleural space. Your chest wall has tension placed on it in a way that it wants to move anteriorly ->.this pulls on the pleura and creates a negative pressure, which also pulls on the alveolar walls keep them open
Pathoma has a really good explanation of this I suggest watching his vid if you have a subscription