Enhanced atmospheric methane oxidation (EAMO) builds on the atmosphere’s natural cleansing process.Nature removes methane continuously in the troposphere by oxidizing it, converting it to mostly water and carbon dioxide. However, today natural oxidation cannot keep up with accelerating methane emissions from both anthropogenic and natural sources. But it’s possible to increase the natural rate of methane oxidation in the atmosphere. This could not only rapidly lower atmospheric methane, it could also cut harmful ground-level ozone.
When the sun shines on airborne sea salt particles, chlorine atoms are generated naturally through photolysis. One promising EAMO method involves adding a small amount of iron to that process. That causes iron trichloride (FeCl3) to form on the salt particles, accelerating the photolysis reaction. Photocatalysis, as the accelerated process is known, can increase the number of chlorine atoms generated in photolysis tenfold. The chlorine atoms in turn increase the rate of methane oxidation, which converts methane to mostly water and some carbon dioxide. Then the sea salt particles fall back into the ocean.
EAMO methods such as this can help restore methane oxidation rates, which are declining due to changes in human activity. Some of those human activities are desirable or unavoidable. For example, replacing fossil fuels with clean energy will have the unintended side-effect of reducing hydroxyl radical production and lowering methane oxidation rates (more on that below), but we must do it anyway. Governments outlawed ozone-destroying chemicals reduced the “hole” in the stratospheric ozone layer, which reduced the amount of ultraviolet light coming through. That in turn reduces the generation of hydroxyl radicals that drive atmospheric methane oxidation. Biomass burning, including forest fires over which we have little control, releases methane and generates carbon monoxide, which consumes hydroxyl radicals.
Beyond positive climate impacts, EAMO has additional co-benefits. Reducing methane also reduces formation of ground-level ozone, of which methane is a key ingredient. Ozone is a powerful greenhouse gas in its own right, and a dangerous air pollutant that damages respiratory health. Studies show reducing ozone by 45% could prevent 260,000 premature deaths, 775,000 asthma-related hospital visits, and 73 billion hours of lost labor from extreme heat. It would also raise crop yields by 25 million tons annually by stopping the harmful impact of ozone on plant growth.
EAMO might also be used to reduce methane emissions at their sources, for example at rice paddies, which are large emitters. Fertilizing rice paddies with iron could potentially reduce their methane emissions, while also fortifying the crop with iron and combatting anemia, a serious public health issue in many developing countries.