We are not aware of the use of source apportionment studies or local monitoring campaigns to assess surrogates. While it may be feasible, there are a lot of parameters that could impact the emissions spatially for this sector such as the emission factors for the various appliances (e.g., wood stoves, pellet stoves, hydronic heaters, fireplaces), the amount of wood burned in them, and the appliance distributions. There is also the meteorological data and resolution of the modeling. We are aware that Ben Murphy of ORD is conducting research using measurement campaigns and CMAQ to assess RWC but not with a surrogate focus. With respect to assessing surrogates, we do assess them by creating maps, and sometimes zoom into areas to do visual comparisons. We did this to compare ACS with a data source of building structures in parts of California; this led to our desire to further pursue available building footprint data to develop a building structure-based surrogate