Atmospheric Discharge Caused by Methane Emission in Permafrost Degradation Area Caused Wildfire
Authors: Shan Wei , Xu Zhichao , Guo Ying , Zhang Chengcheng 
Published: May 2021

With the development of global warming, the carbon pool in the degraded permafrost zone around the Arctic will gradually be disturbed and enter the atmosphere in the form of methane gas. The frequency and intensity of forest fires will gradually increase, and the release of geological methane will become important factors affecting wildfires in permafrost regions. The northwestern section of China's Xiao Xing'an Mountains, which is located in the degradation zone of the southern edge of the permafrost region of Eurasia, was selected as the research area. Monitoring equipment such as atmospheric electric field, air temperature, methane concentration, soil temperature and pore water pressure were deployed to monitor relevant data changes for a long time. Through indoor soil ventilation tests, it was verified that the friction between gas and soil particles caused the difference in soil electric potential, and the analysis revealed the mechanism of seasonal wildfires in the study area. The results show that the gradual decomposition of metastable methane hydrate and stable methane hydrate stored in the permafrost in the northern part of the Xiao Xing'an Mountains in Northeast China is the main source of high-concentration methane gas entering the atmosphere from the surface. In spring, as the frozen layer on the surface of the study area thaws and the snow gradually melts, the high-concentration, high-pressure methane gas accumulated under the frozen layer will be quickly released into the atmosphere. The study area has the annual maximum value of methane concentration on the surface every spring (March to May), and the rapid rise of gas molecules during the decomposition of underground methane hydrate will cause friction with soil particles, causing methane molecules to be positively charged. Under the action of soil pore pressure and the negative charge at the bottom of the near-surface cloud layer, positively charged methane gas enters the atmosphere. The positively charged methane gas in the air contacts the negative charge in the near-surface cloud layer to form a discharge channel to enhance the discharge phenomenon. With the gradual accumulation of positive charges in the air, the positively charged methane in the air near the ground and the water molecules in the air form positively charged aerosols, and contact with the negative charges near the ground will also form a discharge channel to produce a discharge phenomenon, which will lead to high concentrations of methane gas near the surface were ignited. In addition, the mixed gas with higher pressure and concentration will reduce the thermal spontaneous combustion temperature of methane gas, and when methane aerosol is formed, it will further increase the impact on the air temperature, thereby increasing the risk of wildfires. The electric potential difference between the ground and the near-surface and the flammability of methane aerosols caused by the methane gas emission process in the permafrost degraded area will become an important factor in inducing wildfires.