It’s important to note that one reason that transport is so important is both the simultaneous mixing solution and the depth of the first layer. CMAQ has a non-local PBL solution (ACM2) that allows for rapid mixing within the PBL. It also is typically applied with a 20m first layer. In a well-mixed 2km PBL, that means a rapid removal of surface emissions.
This post discusses using an analysis volume to better see the important role of each process.