Estimates Of Anthropogenic Methane Emissions In Nanjing And The Yangtze River Delta

With the proposing of greenhous gas emission reduction targets for various provinces and cities in12th5-Year Plan, widespread attention focuses on city/regional greenhouse gas inventory. In this study, through identifying the emission factors for different sources, the anthropogenic greenhouse gas emissions in Nanjing city and Yangtze River Delta (YRD) region in2009were estimated using the IPCC method. The Monte Carlo method was also applied to calculae the uncertainties of inventories. But, methane emission estimated with the IPCC inventory method at the city and regional scale is subject to large uncertainties. In this study, we determined the CH4to CO2emissions ratio for Nanjing and the Yangtze River Delta (YRD) using the atmospheric CH4and CO2concentrations measured at a suburban site of Nanjing in the winter. The results indicate that:(1) The CH4and CO2concentrations were shown to have pronounced diurnal and seasonal cycles, but the difference between the CH4(or CO2) on weekdays and weekends was not significant. The variations of CO2and CH4concentration on different time scales were controlled by several factors (plants, human and microbial activities; Atmospheric boundary layer stability).(2) There was positive correlation between the CO2and CH4concentrations in Nanjing. The correlation in summer was markedly lower than that in other seasons. In spring, autumn and winter season, the correlations of CH4and CO2of midday were obviously higher than that of the midnight; but in summer, the correlation of midday was lower than that of midnight.(3) The CH4emissions estimated with IPCC method in Nanjing and YRD were1.45×105t and4.87×106t; The CO2emissions in Nanj ing city and YRD region were6.69×107t and1.62×109t.(4) In Nanjing city, the uncertainty intervals of the CH4and CO2emissions reduced by21.7%and24.5%, respectively, after Monte Carlo simulations; In YRD region, the uncertainty intervals of the CH4and CO2emissions reduced by42.9%and18.4%, respectively, after Monte Carlo simulations. Overall, using the Monte Carlo method can significantly reduce the range of uncertainty in estimating CO2and CH4emissions at a city/regional scale.(5) The atmospheric estimate of CH4emissions was in reasonable agreement with that calculated by IPCC method for YRD (within8%) but was160%greater than the latter for the municipality of Nanjing. The most likely source of the discrepancy was unmanaged landfills omitted by the official statistics on garbage production.