Effect of emission changes in Southeast Asia on global hydroxyl and methane lifetime

We performed model studies on how anthropogenic emission changes in Southeast Asia (region between 60–150◦E and 10◦S–50◦N) in the period 1980–2020 could contribute to changes in hydroxyl and methane lifetime on a global scale. From 1980 to 2000, we calculate small global OH and methane lifetime changes due to compensating effects by emission changes in Southeast Asia and emission changes in the rest of the world. There is no guarantee that this offset will persist in the future. Southeast Asia is going through rapid economic development and emission increases there may be a major driver for changes. The development of Asian emissions after year 2000 is under much debate and for this period we apply several emission scenarios. For most emission scenarios the simulated Southeast Asian induced changes in global hydroxyl and methane lifetime after year 2000 are moderate. However, an upper estimate assuming very high increases in NO_x emissions results in substantial increases of hydroxyl and corresponding reductions in global methane lifetime. Interestingly, for the high NO_x emission case our results fit very well with recent satellite observations on trends of NO₂ over central eastern China.