This experiment shows that carbonate concentrations are negligible at most Interagency Monitoring of Protected Visual Environments (IMPROVE) monitoring sites. Even when present, carbonate does not cause significant biases in total carbon (TC), organic carbon (OC), and elemental carbon (EC) concentrations in the IMPROVE protocol. The analysis also shows that acidification to remove interferences from carbonates is not necessary when using a thermal evolution method in which the highest temperature is less than 800¿C. Seventy-seven samples with the highest calcium concentrations from 58 sites in the IMPROVE network were analyzed for carbonate by acidification. Measured carbonate carbon concentrations at most sites were 800¿C temperatures are applied during thermal evolution carbon analysis.