Anthropogenic CH4 Emissions in the Yangtze River Delta Based on A “Top-Down” Method

Abstract

There remains significant uncertainty in the estimation of anthropogenic CH 4 emissions at local and regional scales. We used atmospheric CH 4 and CO 2 concentration data to constrain the anthropogenic CH 4 emission in the Yangtze River Delta one of the most populated and economically important regions in China. The observation of atmospheric CH 4 and CO 2 concentration was carried out from May 2012 to April 2017 at a rural site. A tracer correlation method was used to estimate the anthropogenic CH 4 emission in this region, and compared this "top-down" estimate with that obtained with the IPCC inventory method. The annual growth rates of the atmospheric CO 2 and CH 4 mole fractions are 2.5 ± 0.7 ppm year −1 and 9.5 ± 4.7 ppb year −1 , respectively, which are 9% and 53% higher than the values obtained at Waliguan (WLG) station. The average annual anthropogenic CH 4 emission is 4.37 (± 0.61) × 10 9 kg in the YRD (excluding rice cultivation). This "top-down" estimate is 20-70% greater than the estimate based on the IPCC method. We suggest that possible sources for the discrepancy include low biases in the IPCC calculation of emission from landfills, ruminants and the transport sector.Atmosphere 2019, 10, 185 2 of 21 activities and sums up the individual components to the domain of interest. One problem is that activity data, such as landfill and livestock, and emission factors cannot be accurately determined at the regional and the city scale [8][9][10]. A study in Beijing found that the uncertainty caused by landfill accounts for nearly half of the total uncertainty in the CH 4 emission estimate [11]. Accurate and timely calculations of anthropogenic CH 4 emissions at the regional scale are necessary for assessing the effectiveness of emission reduction policies.Anthropogenic greenhouse gas emissions can also be estimated from observations of the gaseous concentrations in the atmosphere ("top-down" methods). The "atmospheric method" used in this study is one of the "top-down" approaches. One reason for using the atmospheric method is that many sources of anthropogenic CH 4 cannot be quantified with traditional methods, such as the chamber method [12][13][14]. The atmospheric method requires simultaneous concentration measurements of the target gas (CH 4 ) and a tracer gas (usually CO 2 ) when there is no disturbance from sinks or other natural sources [15]. In an observational study using aircraft profile measurement over a broad region of Alaska and Canada, the concentrations of CH 4 and CO 2 increase synchronously with height, showing a strong positive correlation between the two gases [16]. A similar positive relationship also exists in the surface air in a moderately polluted urban atmosphere of Boulder, USA [16]. The explanation for the positive relationship is that the two gases share common source areas and undergo the same long-range transport [17,18]. The concentration ratio between the two gases were used to estimate the CH 4 emissions in the densely populated urban areas in Southern California, showing ...

Seasonal Variations of CH4 Emissions in the Yangtze River Delta Region of China Are Driven by Agricultural Activities

“…In cold seasons, CH 4 emissions from natural sources in the region, such as wetlands and lakes, are negligible (Shen et al, 2014;Hu et al, 2019;Huang et al, 2019). However, during warm seasons, CH 4 emissions from wetlands and other water bodies are large and cannot be ignored (IPCC, 2001;Ding and Cai, 2007).…”

“…The CH 4 emissions using a California-specific inventory were underestimated by 37% compared to top-down atmospheric inversions estimated for central California (Zhao et al, 2009). Top-down inverse approaches have also shown that emission inventories are biased low for China (Shen et al, 2014;Huang et al, 2019). However, one study found that the total CH 4 emissions estimated using an atmospheric Bayesian inversion were 29% smaller compared to EDGAR estimates in China and attributed the bias to an overestimation of CH 4 emissions from rice agriculture during the summer (Thompson et al, 2015).…”

Estimation of greenhouse gas emission factors based on observed covariance of CO2, CH4, N2O and CO mole fractions

“…If the emission of any of the substances is known then that of the others can be calculated from the relationship. The correlation method belongs to the "top-down" ones, and it has been widely used for a long time (see e.g., [17][18][19][20][21][22][23][24][25]). This method is especially applicable for the estimation of the anthropogenic emission in wintertime when the biological activity and photochemical production providing the natural sources of the major anthropogenically influenced greenhouse gases are low.…”

“…Consequently, if the emission of one of the gases is known with reasonable confidence then that of the others can be calculated. Such a "top-down" atmospheric method has already been used for different substances in different parts of the world [19][20][21]23]. Figure 5 shows the correlations between the gases studied.…”

Lower Atmosphere Meteorology

“…Trace gases retrieved using ground-based remote sensing instruments are presented in Javed et al [12], who discuss the relationship between NO 2 and CHOCHO with different meteorological parameters and show the significant decreasing trend of these trace gases in the afternoon. Huang et al [13] analysed a correlation "top-down" procedure to estimate anthropogenic CH 4 emission using long-term atmospheric CH 4 and CO 2 concentration data. Moreover, the results were compared with the frequent "bottom-up" IPCC inventory procedure.…”