1B: Chemical feedback from decreasing carbon monoxide emissions affects methane lifetime

Chemical feedback from decreasing carbon monoxide emissions affects methane lifetime and secondary chemical production of carbon monoxide

A study by Gaubert et al., 2017, found that decreasing CO concentrations over 2002 to 2013 due to reductions in primary emissions of CO from anthropogenic and natural combustion sources have the effect of reducing the lifetime of atmospheric methane (CH4) through CH4 chemical loss by increases in the hydroxyl radical (OH) abundance. In the tropics, this enhanced loss of CH4 leads to an increase in the secondary production of CO. This study assimilated MOPITT carbon monoxide (CO) observations along with meteorological data to create a “CO reanalysis”. A control run with specified CO from the reanalysis was used to test the influence of meteorology on the CH4 lifetime and chemistry. Compared to the run without changes in CO, the lifetime of CO was reduced by 8% over the 12 years. This analysis suggests that the growth rate in CH4 would likely be higher over this time period if CO emissions had not decreased and that assessments of CH4 emissions and abundance need to account for this effect.

Figure 1. Trend components of the tropical and tropospheric column
Figure 1. Trend components of the tropical and tropospheric column integrated column of CO burden (TgCO yr−1), CH4 lifetime (months), CO chemical production (TgCO yr−1) from three simulation experiments. Solid lines represent linear fits to the model results.

Reference:

Gaubert, B., Worden, H. M., Arellano, A. F. J., Emmons, L. K., Tilmes, S., Barré, J., Martinez Alonso, S., Vitt, F., Anderson, J. L., Alkemade, F., Houweling, S., Edwards, D. P. (2017). Chemical feedback from decreasing carbon monoxide emissions. Geophysical Research Letters, 44, 9985–9995. https://doi.org/10.1002/2017GL074987