Big disparities in CH4 emission patterns from landfills between the United States and China and their behind driving forces

Abstract

Waste is the bridge linking resource consumption and greenhouse gas generation, and waste landfills are the main anthropogenic source of methane (CH₄). The United States (US)-China Joint Glasgow Declaration and the Global Methane Pledge are committed to reducing tractable CH₄ emissions; however, differences between the involved countries as well as their generation forecast processes have hampered cooperation. In this study, we provide a deep insight into CH₄ emissions from municipal solid waste (MSW) landfills and identify the disparities in CH₄ emissions with local socio-economic conditions. The US and China, the world's two largest economies, generated approximately 3.73 and 1.48 million tonnes of CH₄ from 1248 to 1955 landfills in 2012 using the FOD/bottom-up method, with corresponding 26.93 and 11.94 kg per tonne waste and emission value from each landfill ranging between 10⁰ and 10⁵ and 10^-5-10⁵ tonnes. The spatial distribution was also quantified and compared with national, state/province, and urban agglomeration perspectives based on historical MSW variations (1990-2015) to clarify the triangular relationship between the economic situation, waste properties, and landfill CH₄ emissions. High-density CH₄ emission regions spatially overlapped with highly developed urban agglomerations, positively correlated with the local gross domestic product (GDP) and population (p < 0.01), with more emissions generated per thousand US dollars in the US (0.25 tonnes) than in China (0.16 tonnes). The US tertiary industry and China's secondary industry contributed to high CH₄ emissions from the waste sector. The increase in tertiary industry might reduce the waste sector's CH₄ emissions. This study will help to understand this new triangular relationship and predict future patterns of CH₄ emissions.

Keywords: Big disparities; Landfill CH4 emissions; Municipal solid waste; Socio-economic conditions; The United States and China.

Graphical abstract

Fig. 1

Frequency distributions of landfill CH₄emissions for eight economic regions in the US and China. The left and right side of violin plots represent the emission distributions of the US and China, respectively; The box plots inside violins show the first, second (median value), and third quartiles of the emissions; The numbers of landfill sites in each region are shown in parentheses; the regions are listed in a GDP ascending order from left to right; RM: Rocky Mountain, NE: New England, PL: Plains, SE: Southeast, GL: Great Lakes, ME: Mideast, FW: Far West, SW: Southwest; NW: Northwestern, NEC: Northeastern, SWC: Southwestern, MY: Middle Yellow River, MYR: Middle Yangtze River, SC: Southern coastal, NC: Northern coastal, EC: Eastern coastal.

Fig. 2

Geographic spatial patterns of landfill CH₄ emissions in the US (a) and China (b) based on kernel density estimation.

Fig. 3

The total emissions (tonnes) (a), per-GDP emissions (kg/1000 USD) (b), and urban per-capita emissions (kg/capita) (c) of landfill CH₄ for eight economic regions in US and China. SW: Southwest, FW: Far West, ME: Mideast, GL: Great Lakes, SE: Southeast, PL: Plains, NE: New England, RM: Rocky Mountain; EC: Eastern coastal, NC: Northern coastal, SC: Southern coastal, MYR: Middle Yangtze River, MY: Middle Yellow River, SWC: Southwestern, NEC: Northeastern, NW: Northwestern.

Fig. 4

Correlation relationship between landfill CH₄ emissions and socio-economic factors in US (n = 51) and China (n = 31).

Fig. 5

The practical (CH₄-pra) and predicted (CH₄-pre) CH₄ emissions based on double logarithmic regression model in US and China.