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Page 14 of 18 Shang et al. Carbon Footprints 2025, 4, 24 https://dx.doi.org/10.20517/cf.2025.28

The study also relies heavily on government reports and statistical yearbooks for activity data. Due to
incomplete local guidelines, reference standards are mainly derived from zonal calculations based on
national-level standards. This approach can lead to significant parameter discrepancies among neighboring
provinces in different zones, thereby introducing uncertainty into the results. It should also be noted that
the analysis is limited to methane emissions from non-industrial waste sources. Methane emissions from
agricultural straw are estimated only for energy use and exclude emissions from the natural decay of straw
returned to fields, which cannot be systematically monitored across regions. This omission may cause
deviations from actual emission levels. Similarly, methane from small-scale livestock manure is excluded,
with the analysis limited to emissions from livestock and poultry breeding. In the municipal solid waste
sector, only methane emissions from landfilling are considered, while emissions from other treatment
processes are not quantified. Consequently, variations in parameter values may result in discrepancies
between the total methane estimates in this study and those reported in other domestic or international
inventories, as well as those derived from atmospheric inversion data (see Section "Comparison with other
studies").

Policy implications and insights
Methane emissions from waste disposal in China have declined significantly over the past five years, largely
due to the "Waste-Free City" initiative and the expansion of waste incineration facilities nationwide. These
measures have substantially reduced landfill volumes in both urban and rural areas. In 2018, China
launched the waste-free city initiative, urging regions to minimize landfill use. The following year, a waste-
sorting campaign was implemented, accompanied by a series of action plans aimed at reducing waste and
improving resource utilization. Together, these policies have driven a nearly three-quarters reduction in
landfill volumes over the past five years, with methane emissions from waste disposal falling accordingly
from 42.9% to 15.5%. Looking ahead, as waste incineration capacity continues to expand, methane
emissions from waste disposal are expected to decline further. By contrast, methane emissions from
agricultural planting waste have exhibited a slight increase, reflecting the stability of China's agricultural
structure and straw production. Despite the enforcement of bans on open straw burning since 2018 and the
return of much agricultural waste to fields for reuse, this source of methane emissions remains outside the
scope of the present study. Off-field utilization of straw for fuel is still limited, as it depends heavily on
technological advances and policy support, and has been promoted only in select regions. Nevertheless, over
the past five years, emissions from agricultural planting waste have overtaken those from other sources,
making it the leading contributor to methane emissions. This shift highlights the agricultural sub-sector as a
priority for future methane mitigation. Livestock manure is now the second-largest source of methane
emissions from waste. With rising consumption of meat, eggs, and dairy products, the numbers of beef and
dairy cattle have increased by 27.7% and 7.4%, respectively, over the past five years. Methane generation
from manure is closely tied to livestock populations. However, large-scale pig farming in China remains
relatively limited, with much of the production carried out by households, cooperatives, or small and
medium-sized farms. As a result, the collection and utilization of methane from manure remain inadequate,
posing an ongoing challenge for methane reduction. Methane emissions from sewage treatment systems
have grown most rapidly, driven by improvements in urban drainage systems that have greatly expanded
sewage collection and treatment capacity. The sewage treatment considered in this study refers primarily to
municipal sewage, with methane emissions arising mainly under anaerobic conditions in pipelines and
sludge treatment. Thus, the potential for methane generation from sewage depends largely on COD
emissions from domestic water use. In the future, as sewage treatment facilities continue to expand in both
urban and rural areas, the volume of sewage collected and treated will increase, further unlocking the
potential for methane emissions.