Accurate emission line fluxes of planetary nebulae (PN) provide important constraints on the nature of the late stages of stellar evolution. Large (r > 10'), diffuse PN may trace the latest stages of PN evolution, where material from the AGB wind is returned to the interstellar medium. However, the low surface brightness and spatially extended emission of large PN have made accurate measurements of line fluxes difficult with traditional long-slit spectroscopic techniques. Furthermore, the distinction of these nebulae from HII regions, supernova remnants, or interstellar gas ionized by a hot, evolved stellar core can be challenging. Here, we report on observations of > 20 large PN with the Wisconsin H-Alpha Mapper (WHAM), a Fabry-Perot spectrograph designed to detect faint, diffuse optical emission with high sensitivity and spectral resolution (R ≈\ 25,000). Our sample includes newly revealed Hα \ enhancements from the MASH and WHAM surveys. We present emission line fluxes of Hα , Hβ , [NII]λ 6583, and [OIII]λ 5007, and compare our data to previous measurements. We use the emission line ratios and kinematics of the ionized gas to characterize and identify the nature of the nebulae.