Quantification and assessment of environmental and health risk in post-combustion carbon capture: an Australian study

Post-combustion carbon capture (PCC) technology is an innovation technology to capture carbon dioxide (CO2) from flue gas through solvents absorption typically using monoethanolamine (MEA). PCC technology is a facility installed after the combustion units. In Australia, most power stations are coal-burning power stations. PCC technology is more likely to be applied on these stations to reduce CO2 emissions into the atmosphere. However, the technology also emits amine and its degradation products into the atmosphere. Amine can react with OH radicals to form nitrosamine and nitramine under photolysis. A review of literatures in human health impacts reveals that nitrosamine is suspected to be human carcinogenic and aldehydes as the degradation products of amine are known to be toxic. In addition, PCC technology emits ammonia, which is a contributor to fine particle formation. In order to assess potential environmental and human health impacts from the technology, this study hypothesizes a PCC project in Bayswater Power Station in the Upper Hunter region, NSW, Australia and conducts many tasks including an experimental sampling of aldehydes, KPP modelling simulation for amine’s chemical scheme, atmospheric dispersion simulations for amine, nitrosamine, nitramine and other primary air pollutants, and risk assessments of formaldehyde and PM2.5. In the experimental sampling of aldehydes, the study used an active sampling system to conduct air sampling of aldehydes following TO-11A method to determine baseline concentrations of aldehydes on MU campus and in Upper Hunter industrial area. The measured concentration was further used to represent the background value of formaldehyde and acetaldehyde in TAPM-CTM setting. The measured average daily HCHO concentration was 2.2 ppb in late spring, 1.1 ppb in summer, 1.3 ppb in late autumn, and 0.5 ppb in winter on the MU campus. Ambient acetaldehyde concentrations on the MU campus were only available in summer and winter with mean values of 0.6 ppb and 1.2 ppb, respectively. In the Upper Hunter area, the HCHO values were measured in summer and winter. The average concentration of ambient HCHO was 1.0 ppb and 0.9 ppb in summer and in winter, respectively. The acetaldehyde was only detected in summer with mean value of 1.8 ppb in the Upper Hunter area. Chemical scheme of amine in the atmosphere was simulated in KPP model under two scenarios: chamber scenario and atmosphere scenario. In the chamber scenario, the MEA decreased sharply in the first 3 hours. Nitramines and nitrosamines increased quickly at the beginning of the experiment, then decreased slightly. In the atmospheric scenario, the concentration changes were slower than the chamber experiment. Atmospheric dispersion of amine and its degradation products were simulated in CALPUFF model. The highest concentrations of amines, nitrosamine, and formaldehyde occurred in December which is the hottest months in southern hemisphere. All values of these compounds did not exceed the US EPA’s recommended threshold level for health impacts. TAPM-CTM model was employed to simulate atmospheric dispersion of primary air pollutants in the study area using 2003 NSW emission inventory data under different meteorological conditions. The study assumed a 70% decrease of NOx emissions and a 95% decrease of SO2 emission from the Bayswater Power Station. As there is not emission control of NOx and SO2 in the power station, the decreased NOx and SO2 emission led to a significant decrease on atmospheric NOx and SO2 concentrations. Due to the largely decreased NOx and SO2 emission, the meteorological conditions is likely to play a less significant impacts on the change of near surface concentrations of NOx and SO2. In addition, the increased aldehyde emissions did not significantly change the concentrations of formaldehyde and acetaldehyde. NH3 is reported to be favored reacting with nitrate acid to form nitrate aerosol (NIT) in low temperatures (Ansari and Pandis, 1998; Heo et al., 2015; Pinder et al., 2008). Due to increased NH3 from PCC projects, more nitrate aerosol (NIT) may be formed in low temperature under reactions of NH3 and nitrate acid. The modelled results showed that the average change of NIT were smaller in winter than other months under largely decreased NOx emission. The results indicated nitrate aerosol formation is favored in the low temperature environments. In addition, this study’s results showed the nitrate aerosol formation does not increase linearly with an increase in NH3. PM2.5 formation also did not show a linear relationship with NIT, NH4 or ASO4. To assess the health impacts exposure to formaldehyde and PM2.5, a Monte-Carlo risk model (@RISK) was employed to simulate lifetime exposure to these air pollutants. The cancer risk due to HCHO exposure decreased slightly after PCC technology installation. The mortality risk due to exposure to PM2.5 decreased by 9.3×10-6 and 5.7×10-6 on mortality from all causes diseases and mortality from lung cancer after installing PCC technology, respectively.