5:15 PM - 7:15 PM
[AAS11-P19] Comparative analysis of ground-level methane concentrations in different regions of Japan
Keywords:methane, ground-level observations, satellite observations, emission sources, metrological condition
Methane is one of the most important Short-Lived Climate Forcers (SLCFs) with a relatively short atmospheric lifetime of about 10 years and a Global Warming Potential over 20 years (GWP20) 82.5 times greater than that of carbon dioxide over shorter timescales. Therefore, reducing methane emissions is expected to have an immediate impact on mitigating global warming in the near term. In this study, we investigated the regional differences in ground-level methane concentrations over Japan to identify the emission sources and meteorological factors that influence the regional characteristics of ground-level methane concentrations.
For the comparative analysis, we used hourly methane concentration data from the Japanese Air Pollution Monitoring Stations (JAPMSs) at 17 locations across Japan from 2010 to 2019 (ground-level methane). In addition, variations in ground-level methane concentrations were compared with broad-scale surface methane concentrations obtained from GOSAT satellite observations, GOSAT Level 4B CH4 Data Product (satellite methane), and remote monitoring stations (Ryori, Minamitorishima, Yonagunijima) (remote methane). The satellite methane was used from the grid data including the JAPMSs.
Ground-level methane concentrations showed an increasing trend (2.71~12.3 ppb/yr) at all monitoring stations from 2010 to 2019. In relatively less populated areas such as Nonodake and Omuta, the growth rates were similar to satellite methane concentrations (8.19~8.73 ppb/yr) and remote methane concentrations (7.92~8.56 ppb/yr) for the same period. In contrast, urban areas such as Shinjuku and Osaka showed a significant disparity in the growth rates (2.71~12.3 ppb/yr) to each other, as well as to the growth rates for the satellite and the remote methane concentrations.
Satellite methane and remote methane concentrations decreased in summer and increased in winter, consistent with the average mid-latitude methane concentration trend in the Northern Hemisphere. On the other hand, ground-level methane concentrations showed different seasonal variations depending on the region. For example, methane concentrations in Nonodake and Tobishima showed an increase in summer and a decrease in winter, which can be attributed to methane emissions from rice paddies in these agricultural areas. Matsue, which is located on a lake shore, also shows an increase in summer due to the activation of methane fermentation. These suggest a relationship between the increases in methane concentrations in summer and anaerobic methane production. In contrast, urban areas such as Tokyo and Osaka show seasonal variations similar to the broad-scale trend, but with larger amplitude changes. Coastal areas such as Osaka and Amagasaki showed significant summertime decreases in ground-level methane concentrations influenced by the oceanic air-masses. Densely populated urban areas such as Tokyo and Kawasaki have higher anthropogenic sources of methane emissions. Especially in the winter season, the radiative inversion layers formed lead to a drastic increase of methane at the ground level in the urban areas.
For the comparative analysis, we used hourly methane concentration data from the Japanese Air Pollution Monitoring Stations (JAPMSs) at 17 locations across Japan from 2010 to 2019 (ground-level methane). In addition, variations in ground-level methane concentrations were compared with broad-scale surface methane concentrations obtained from GOSAT satellite observations, GOSAT Level 4B CH4 Data Product (satellite methane), and remote monitoring stations (Ryori, Minamitorishima, Yonagunijima) (remote methane). The satellite methane was used from the grid data including the JAPMSs.
Ground-level methane concentrations showed an increasing trend (2.71~12.3 ppb/yr) at all monitoring stations from 2010 to 2019. In relatively less populated areas such as Nonodake and Omuta, the growth rates were similar to satellite methane concentrations (8.19~8.73 ppb/yr) and remote methane concentrations (7.92~8.56 ppb/yr) for the same period. In contrast, urban areas such as Shinjuku and Osaka showed a significant disparity in the growth rates (2.71~12.3 ppb/yr) to each other, as well as to the growth rates for the satellite and the remote methane concentrations.
Satellite methane and remote methane concentrations decreased in summer and increased in winter, consistent with the average mid-latitude methane concentration trend in the Northern Hemisphere. On the other hand, ground-level methane concentrations showed different seasonal variations depending on the region. For example, methane concentrations in Nonodake and Tobishima showed an increase in summer and a decrease in winter, which can be attributed to methane emissions from rice paddies in these agricultural areas. Matsue, which is located on a lake shore, also shows an increase in summer due to the activation of methane fermentation. These suggest a relationship between the increases in methane concentrations in summer and anaerobic methane production. In contrast, urban areas such as Tokyo and Osaka show seasonal variations similar to the broad-scale trend, but with larger amplitude changes. Coastal areas such as Osaka and Amagasaki showed significant summertime decreases in ground-level methane concentrations influenced by the oceanic air-masses. Densely populated urban areas such as Tokyo and Kawasaki have higher anthropogenic sources of methane emissions. Especially in the winter season, the radiative inversion layers formed lead to a drastic increase of methane at the ground level in the urban areas.