PM2.5 carbonate concentrations at regionally representative Interagency Monitoring of Protected Visual Environment sites

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 <100 ng m −3 , with many less than lower quantifiable limits; the highest carbonate carbon of 420 ng m −3 was measured at Guadalupe Mountains National Park in western Texas. Comparison of EC measured at 800°C with and without acidification showed no consistent biases for the nonacidified analysis, even when carbonate levels were high. Acidification may be advisable when sampling particle sizes larger than 2.5 μm, when samples are acquired at locations where carbonate carbon is expected to be high, or when >800°C temperatures are applied during thermal evolution carbon analysis.