Quantify the regional methane emissions based on a new SCIAMACHY data set

Methane (CH4) is the most important anthropogenic greenhouse gas after carbon dioxide, and it keeps increasing globally since 2007 after a period of relative stability, which is well-documented by surface measurements and satellites. Although satellites provide long-term global observations of CH4, the interpretation of column-averaged mixing ratios (xCH4) is difficult due to the influence of elevated terrains (i.e. mountain areas) and less abundant methane in the stratosphere. The lack of data over the ocean further limits global insights. Here we build a long-term global CH4 data set at a resolution of 0.25° × 0.25°  from SCIAMACHY, including the areas over the ocean, with the help of FRESCO cloud data. We dynamically consider the influence of elevations and contributions from the stratosphere through converting xCH4 to tropospheric xCH4 (trop_xCH4) by applying the daily ratios of tropospheric to stratospheric xCH4 in GEOS-Chem model.

The large increases occur in Trop_xCH4 over the source regions and mountain areas. The trend of SCIAMACHY Trop_xCH4 over the global ocean is comparable to the trend of NOAA globally averaged marine monthly mean data, showing the capability of SCIAMACHY in monitoring the ocean. After removing the latitudinally independent background concentration based on SCIAMACHY data over the ocean, we quantify the regional sources. A significant trend in Trop_ xCH4 relating to the background in Eastern China, India, tropical Africa, and tropical South America is further found from 2003 to 2011.