Greenhouse gas emission analysis and measurement for urban rail transit: A review of research progress and prospects

Rail transit plays a key role in mitigating transportation system carbon emissions.Accurate measurement of urban rail transit carbon emission can help quantify the contribution of urban rail transit towards urban transportation carbon emission reduction.Since the whole life cycle of urban rail transit carbon emission measurement involves a wide range of aspects,a systematic framework model is required for analysis.This research reviews the existing studies on carbon emission of urban rail transit.First,the characteristics of urban rail transit carbon emission were determined and the complexity of carbon emission measurement was analyzed.Then,the urban rail transit carbon emission measurement models were compared and analyzed in terms of the selection of research boundaries,the types of greenhouse gas(GHG)emissions calculation,and the accuracy of the measurement.Following that,an intelligent station was introduced to analyze the practical application of digital collaboration technology and energy-saving and carbon-reducing system platforms for rail transit.Finally,the urgent problems and future research directions at this stage were discussed.This research presents the necessity of establishing a dynamic carbon emission factor library and the important development trend of system integration of carbon emission measurement and digital system technology.

Research on Measurement and Calculation of Carbon Emission from the Production of Prefabricated Building Components

The measurement and calculation of the carbon emission from the production of prefabricated building components were studied.Based on the carbon emission factor method,a carbon emission calculation model of the components in the production phase was established.Besides,the actual measurement method and calculated at rated power method were proposed for the measurement and calculation of carbon emission,and several measurements were carried out in a component factory located in a coastal area of south China and a component factory located in Beijing,respectively.The results of the study show that the carbon emission factors of laminates and wallboards produced by factories located in coastal areas of southern China under natural curing conditions were 7.61 kg CO2/m3 and 5.84 kg CO2/m3 respectively.The carbon emissions conversion coefficients of concrete mixer,reinforcing bar production line and travelling crane between actual operation and with per the rated power were approximately 0.44,0.34 and 0.34 respectively.When the actual measurement cannot be performed,the conversion coefficient can be used to correct the data of the calculated at rated power to make it closer to the true value.The carbon emission factor of the laminated panels produced by the component factory in Beijing under steam curing concrete conditions was 132.15 kg CO2/m3,and the factory is used as a prototype,a complementary steam generation system model of solar energy and boiler was established,and it was calculated that the system can reduce CO2 emissions by about 300 tons throughout the year.

Characteristics of greenhouse gas emission in three full-scale wastewater treatment processes

Three full-scale wastewater treatment processes, Orbal oxidation ditch, anoxic/anaerobic/aerobic （reversed A^2O） and anaerobic/anoxic/aerobic （A^2O）, were selected to investigate the emission characteristics of greenhouse gases （GHG）, including carbon dioxide （CO2）, methane （CH4） and nitrous oxide （N2O）. Results showed that although the processes were different, the units presenting high GHG emission fluxes were remarkably similar, namely the highest CO2 and N2O emission fluxes occurred in the aerobic areas, and the highest CH4 emission fluxes occurred in the grit tanks. The GHG emission amount of each unit can be calculated from its area and GHG emission flux. The calculation results revealed that the maximum emission amounts of CO2, CH4 and N2O in the three wastewater treatment processes appeared in the aerobic areas in all cases. Theoretically, CH4 should be produced in anaerobic conditions, rather than aerobic conditions. However, results in this study showed that the CH4 emission fluxes in the forepart of the aerobic area were distinctly higher than in the anaerobic area. The situation for N2O was similar to that of CH4： the N2O emission flux in the aerobic area was also higher than that in the anoxic area. Through analysis of the GHG mass balance, it was found that the flow of dissolved GHG in the wastewater treatment processes and aerators may be the main reason for this phenomenon. Based on the monitoring and calculation results, GHG emission factors for the three wastewater treatment processes were determined. The A^2O process had the highest CO2 emission factor of 319.3 g CO2/kg CODremoved, and the highest CH4 and N2O emission factors of 3.3 g CH4/kg CODremoved and 3.6 g N2O/kg TNremoved were observed in the Orbal oxidation ditch process.