We consider whether the application of equitable estoppel here, to require the Board to permanently exempt the 20th Street property and Unit 211 of the Ocean Avenue property from rent control regulations, would require the Board to act in excess of its authority. According to 20th Street Owner, the granting of a removal permit exempts rental units from rent control; in other words, section 1803(t) authorizes the Board to exempt rental units from rent control regulations. The plain terms of section 1803(t), however, do not support this position. That section provides that "[a]ny landlord who desires to remove a controlled rental unit from the rental housing market by demolition, conversion or other means is required to obtain a permit from the Board prior to such removal from the rental housing market. " (§ 1803(t), italics added.) A "market" is "[a] place of commercial activity in which goods or services are bought and sold." (Black's Law Dict. (10th ed. 2014) p. 1113, col. 2.) Thus, section 1803(t) "prevent[s] landlords from evicting tenants in order to go out of the residential housing business absent permits from the City and the Board. ( City of Santa Monica v. Yarmark (1988) 203 Cal.App.3d 153, 157, 249 Cal.Rptr. 732 ....)" ( Santa Monica Rent Control Bd. v. Bluvshtein (1991) 230 Cal.App.3d 308, 314, 281 Cal.Rptr. 298.) Removal permits allow "removal from the rental housing market"; they do not allow removal from the rent control market. (§ 1803(t)(1).) " ' "If the words of the statute are clear, the court should not add to or alter them to accomplish a purpose that does not appear on the face of the statute or from its legislative history." ' " ( Goodman v. Lozano (2010) 47 Cal.4th 1327, 1332, 104 Cal.Rptr.3d 219, 223 P.3d 77.)