diff --git a/cara/models.py b/cara/models.py
index 56f663f4..88e5493a 100644
--- a/cara/models.py
+++ b/cara/models.py
@@ -529,7 +529,7 @@ class _ExpirationBase:
     types: typing.ClassVar[typing.Dict[str, "_ExpirationBase"]]
 
     def aerosols(self, mask: Mask):
-        # total volume of aerosols expired per volume of air (mL/cm^3).
+        # total volume of aerosols expired (cm^3).
         raise NotImplementedError("Subclass must implement")