The Administrator may add, by rule, in accordance with the criteria set forth in subsection (a) or (b), as the case may be, any substance to the list of class I or class II substances under subsection (a) or (b). For purposes of exchanges under section 7661f 1 of this title, whenever a substance is added to the list of class I substances the Administrator shall, to the extent consistent with the Montreal Protocol, assign such substance to existing Group I, II, III, IV, or V or place such substance in a new Group.

Periodically, but not less frequently than every 3 years after November 15, 1990, the Administrator shall list, by rule, as additional class I or class II substances those substances which the Administrator finds meet the criteria of subsection (a) or (b), as the case may be.

At any time, any person may petition the Administrator to add a substance to the list of class I or class II substances. Pursuant to the criteria set forth in subsection (a) or (b) as the case may be, within 180 days after receiving such a petition, the Administrator shall either propose to add the substance to such list or publish an explanation of the petition denial. In any case where the Administrator proposes to add a substance to such list, the Administrator shall add, by rule, (or make a final determination not to add) such substance to such list within 1 year after receiving such petition. Any petition under this paragraph shall include a showing by the petitioner that there are data on the substance adequate to support the petition. If the Administrator determines that information on the substance is not sufficient to make a determination under this paragraph, the Administrator shall use any authority available to the Administrator, under any law administered by the Administrator, to acquire such information.

Only a class II substance which is added to the list of class I substances may be removed from the list of class II substances. No substance referred to in subsection (a), including methyl chloroform, may be removed from the list of class I substances.