Abstract: Objective　Amine-based chemical absorption technology is currently the most mature and widely deployed carbon capture approach. However, during operation, amines inevitably escape with flue gas in both gaseous and aerosol phase, leading to solvent loss, operational challenges, and environmental and health concerns. Despite increasing attention to these emissions, there is still no standardized offline sampling protocol, and the performance and limitations of existing wet-impinger techniques remain insufficiently assessed. In addition, ammonia (NH3), as the major degradation product of amine solvents, may be co-emitted in routine monitoring. Therefore, this study aims to: (i) design and construct a specialized offline sampling device suitable for high-humidity carbon-capture flue gas and capable of simultaneously collecting organic amines and NH3; (ii) systematically evaluate the sampling performance of the device under controlled laboratory conditions, including the influence of impinger configuration, absorption solution chemistry, and aerosol-nuclei levels; (iii) demonstrate the applicability of the optimized device system in full-scale carbon capture facilities, providing foundational data for future method standardization. Methods　A modular offline sampling device was developed, consisting of a heated sampling line, temperature-controlled impingers, a drying unit, filtration components, and calibrated flow-control equipment. Two 500 mL impingers were compared. One was a conventional design, and the other was a baffle-plate impinger engineered to enhance the capture of droplet and aerosol through high-speed impaction. Absorption solutions including deionized water and dilute H2SO4 (0.25%) were evaluated to determine their effectiveness in retaining both amines and NH3, particularly under actual sampling volumes. A TSI 3076 atomizer was used to generate test aerosols containing monoethanolamine (MEA), and three representative concentrations of NaCl were introduced to simulate various levels of condensation nuclei. A filter–impinger hybrid configuration was used to distinguish aerosol-phase from amine emissions. All captured species, including MEA, 2- amino-2-methyl-1-propanol (AMP), piperazine (PZ), and NH3, were quantified using Metrohm ion chromatography with optimized C6 and C4 columns. Finally, the validated device was deployed at four full-scale carbon-capture installations in China, covering coal-fired and gas-fired units employing MEA-, AMP-, and PZ-based solvents. Results and Discussion　Laboratory results showed that the design of impinger had a decisive influence on amine collection. The baffle-plate impinger reduced the breakthrough of downstream MEA to below 5%, while the conventional impinger exhibited the breakthrough exceeding 30% even when two units were used in series, which indicated that conventional impingers may under-collect amines in actual flue-gas conditions. For NH3, dilute H2SO4 achieved complete capture, whereas water allowed extensive breakthrough, confirming that acidic absorption solutions are essential for simultaneous amine and NH3 monitoring. It was found that the presence of condensation nuclei significantly altered emission characteristics. Specifically, with the increase of NaCl concentration, the aerosol-phase fraction of MEA increased from 6% to 20%, and the total MEA emissions also increased. This highlights that the formation of aerosols, enhanced by nucleation precursors, is a key pathway for solvent loss and should be explicitly considered in emission assessments. These findings are consistent with prior reports, but provide quantitative laboratory evidence under controlled conditions. Field sampling demonstrated that all examined carbon-capture facilities had considerable amine emissions. Among them, MEA emissions ranged from 5.18 to 17.5 mg/m3, AMP ranged from 0.76 to 35.9 mg/m3, and PZ was around 0.21 mg/m3. NH3 emissions varied between 5.70 and 27.1 mg/m3, far exceeding the regulatory limit for NH3 emission in selective catalytic reduction (SCR) systems (2.3 mg/m3). These results confirm that both amines and NH3 are important emission constituents, and their degradation processes within absorber and stripper columns contribute substantially to overall atmospheric release. The device performed reliably under different plant types, solvent formulations, and operational conditions, demonstrating its robust field applicability. Conclusion　This study presents a specialized offline sampling device for quantifying amines and NH3 in carbon capture flue gas. Through systematic laboratory evaluation, the study clarifies the importance of impinger configuration, identifies dilute H2SO4 as an effective absorption medium for simultaneous pollutant capture, and quantifies the influence of condensation nuclei on the aerosolization of amines. In addition, field measurements of four carbon capture units validate the device's operational reliability and reveal substantial emissions of both amines and NH3. Overall, the developed method provides a practical and reliable tool for emission monitoring of amines and NH3 and strong technical support for future standardization efforts in amine-based carbon-capture systems.

Key words: carbon capture, amine emissions, offline measurement, emission characteristics