A total of 2,058 wet wipe samples were collected from 343 houses in northern California that were potentially impacted by one of 22 wildfires. The samples were analyzed for char, ash and soot. Char was detected in 368 (17.9%) of the 2,058 wet wipe samples, ash was detected in 37 (1.8%) samples, and soot was only detected in four samples (0.2%). Char was the only residue useful for evaluating exposure of the structure to wildfire plumes and for evaluating the impact of wildfire smoke residues during that period of time. About 84% of exterior surface samples and 75% of interior samples that were positive for char were collected within two miles of the wildfire. Average char concentrations declined with elapsed time, and this factor should be considered when estimating initial conditions
