The present invention provides apparatus and methods for adjusting the atmosphere within a substantially sealed chamber containing respiring produce. The chamber of the present invention includes inlet means to permit ambient atmosphere to enter the chamber, and outlet means to permit chamber atmosphere to exit the chamber. Methods using apparatus of the present invention comprise: (a) monitoring the oxygen concentration within the chamber; (b) following detection that the oxygen concentration in the chamber has fallen below a predetermined amount, opening the inlet means so that the amount of oxygen in the chamber increases; and (c) removing carbon dioxide from the chamber atmosphere substantially at a predetermined rate, the predetermined rate having been selected such that the carbon dioxide concentration within the chamber atmosphere does not substantially exceed a predetermined amount. The methods may also comprise opening the inlet means for a time that is approximately proportional to the difference between the detected oxygen concentration and an oxygen setpoint.