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The results of a 30-year study show that the Earth's atmosphere has strengthened its natural ability to clean itself of pollutants: since the late 1990s it has become more efficient at removing methane, a greenhouse gas that contributes to climate change. An international research team, including Olaf Morgenstern of the National Institute of Water and Atmospheric Research and Martin Manning of Victoria University (both in New Zealand), analyzed long-term measurements of carbon monoxide (or carbon-14 (14C)) from two remote stations, Barring Head, New Zealand, and Arrival Heights, Antarctica.
The key role in the self-cleaning of the atmosphere, as it turned out, is played by the hydroxyl radical (OH), which extremely quickly enters into chemical reactions with most polluting gases and converts them into less dangerous compounds. The results of the scientific work were published in the journal Nature Communications.Since direct measurements of OH are difficult, scientists used 14CO as an indicator and used it to indirectly estimate the concentration of OH in the Earth's atmosphere. The fact is that this rare isotope, formed under the influence of cosmic rays, is almost completely "removed" from the atmosphere by hydroxyl radicals.
The results showed that after 1997, the normalized 14CO data gradually decreased: at Baring Head, the average annual decrease was 0,5 percent (about 12 percent for the period from 1997 to 2022), and in Antarctica — especially in December and January — it reached 1,8 percent per year (about 43 percent for the period from 1997 to 2021). These negative trends mean that the concentration of hydroxyl radicals in the atmosphere is increasing: the higher the level of OH, the faster the atmosphere is cleared of pollutants. Therefore, its oxidizing capacity has increased significantly in recent decades.
The results of computer modeling (using the modern climate model NIWA-UKCA) confirmed: the increase in OH concentrations in the atmosphere is occurring globally and may be associated with factors such as increased concentrations of nitrogen oxides (NOₓ) emissions, ozone depletion, and rising temperatures (all of which contribute to the formation of hydroxyl radicals).
But an increase in methane concentration leads to a decrease in OH concentration, since methane is their main “sink”. Thus, to maintain the chemical balance of the planet, even greater emissions of this greenhouse gas may be required. The results of the new scientific work will not only help to better understand the dynamics of the chemistry of the Earth's atmosphere, but will also affect climate models and strategies for reducing greenhouse gas emissions.
