Chinese Coal Mines Methane Emissions Constrained by High-Frequency Measurements

Methane’s high Global Warming Potential (GWP) and short atmospheric life relative to carbon dioxide have led to methane mitigation as a cost-effective and realistic near-term action that serves as a bridge to longer-term mitigation options. This paper calculated coal mine methane (CMM) emissions from 636 individual coal mines in Shanxi Province based on the Intergovernmental Panel on Climate Change (IPCC) Tier 2 approach. 5 sets of emission factors were used to compile this bottom-up inventory. Each coal mine is classified into 3 different coal mine gas ranks based on the method issued by the National Coal Mine Safety Administration and the National Energy Administration. Haft-hourly eddy-covariance measurements of methane flux from 1 mine (xhv) over a 5-month period were used to quantify and constrain the high-frequency variation in emissions. From the perspective of probability density, 15.5% of the total data is covered by the boxes overlapping the different bottom-up emissions estimates, while 53.5% of the total data falls in the single box below the floor of the bottom-up measurements. The in-situ measurements offer scaling factors (RATIO correction) for updating the preliminary bottom-up coal mine methane emissions datasets. A statistical approach is applied to individual coal mines by grouping them by coal mine gas rank. From the perspective of cumulative probability, the CMM flux shows a pattern that low gas rank < high gas rank < outburst rank. We have compared the CMM emissions with EDGAR-COAL and GFEI. In 2019, the EDGAR and GFEI inventory results show that methane emissions from coal mines in Shanxi Province are 7.27 Tg and 6.29 Tg, respectively. Our results range from 4.41-7.63 Tg. In Changzhi city, over the region in which this dataset has emissions that EDGAR-COAL and GFEI do not identify the emissions are [44.35,125.60,354.02] and [398.22,1125.81,3185.22] with the unit in ug (m^-2 s^-1), respectively. The values in brackets are results after RATIO correction, corresponding to cumulative percentages 30, 50 and 70 respectively. Over the region that EDGAR-COAL has misidentified coal mines, the emissions are 128.27 ug (m^-2 s^-1). Over the region that EDGAR and our inventory both have emissions, the EDGAR-COAL emissions are 357.65 ug (m^-2 s^-1), while our emissions are about 353.87 ug (m^-2 s^-1). Over the region where GFEI has misidentified coal mines, the emissions are 181.18 ug (m^-2 s^-1). Over the region that GFEI and our inventory both have emissions, the GFEI emissions are 164.04 ug (m^-2 s^-1). There are no regions where we have emissions while GFEI has no emissions in Changzhi city. These facility-level inventories can help identify mitigation opportunities at specific mines, and support the design of more effective policies.