Increasing levels of atmospheric CO2 emissions from fossil fuel combustion is altering global climate, and several strategies are being examined for CO2 capture and sequestration. Aqueous amine solutions, in particular, monoethanolamine (MEA) is extensively used for CO2 adsorption. Our objective in this study was to follow the reaction of CO2 with 15 wt % monoethanolamine (MEA) by horizontal attenuated total reflection Fourier transform infrared spectroscopy (HATR-FTIR), with particular focus on the evolution of MEA, protonated MEA (MEAH(+), MEA carbamate, and carbonate/bicarbonate species. Since the path length in HATR-FTIR is well-defined, by use of standards and Beer's law, the molar absorptivity was calculated. This allowed us to monitor the concentrations of MEA and MEAH(+) quantitatively. Using the characteristic infrared bands of the various amine-derived species, influence of SO2 (151 ppm) on CO2 absorption by MEA was studied, including the cycling process of adsorption (40 degrees C) and desorption (100 degrees C). No effect of SO2 was noted on CO2 uptake by MEA. With blends of piperazine and MEA, the CO2 loading increased, and evolution of vibrational bands due to MEA species was slower in the presence of piperazine.