Mix lemon zest, salt, and citric acid. Pound the mixture with a Mortar and Pestle, if necessary, to combine the flavors.
Use right away, or freeze until needed. Or better yet, make it in small batches as needed.
Notes
This sumac substitute recipe is not meant for a permanent swap for sumac powder. It's meant to be used in a pinch when a recipe calls for a small amount of sumac.
Sumac powder should be stored in the freezer, especially if you don't use it very often. Some sumac powders have more moisture than others and tend to spoil when stored like the rest of your spices.
Sumac comes in a variety of shades from bright red, to a deep shade of purple. The grind also varies from fine to coarse. The color or texture, however, does not affect the flavor.