Ammonia drives cloud formation – University of Innsbruck
The increased use of artificial fertilizers and fog from animal husbandry brings more ammonia into the atmosphere. During the Asian monsoon, ammonia from agricultural sources is increasingly transported to the upper troposphere. There, the air pollutant accelerates the formation of particles and thus the formation of clouds.
Whether and how many clouds are in the sky has a major impact on how the earth continues to warm up. To date, quantifying this effect in climate models is associated with great uncertainties. This is mainly due to the fact that the formation of condensation nuclei in the atmosphere is not sufficiently understood. Since 2009, an international team has voted for the Large-scale experiment CLOUD at the European nuclear research center CERN near Geneva, the molecular mechanisms of the formation of new particles from atmospheric gases, from which condensation nuclei for clouds form. In a current Studying in the journal Nature the scientists now show that the presence of ammonia in the upper troposphere can lead to increased formation of particles.
Ammonia drives cloud formation
The troposphere is the lowest layer of the earth’s atmosphere and extends to around 15 kilometers above the earth’s surface. The upper troposphere plays an important role in the climate system. It is precisely here that small changes in the composition have a significant impact on the Earth’s radiation budget. If new particles are formed here, more clouds are formed. “However, the precursor gases that drive this process of particle formation are not well understood,” emphasizes Armin Hansel from the Institute for Ion Physics and Applied Physics at the University of Innsbruck, one of the co-authors of the current study. “With experiments carried out under upper tropospheric conditions in the CLOUD chamber at CERN, we have now been able to show that nitric acid, sulfuric acid and ammonia together form particles at a rate that is faster than if only two of the three components react with each other,” says Hänsel.
The importance of this mechanism for cloud formation therefore depends on the amount of ammonia present. Until now, it was assumed that ammonia was washed out as the air masses rose. Recently, however, surprisingly high concentrations of ammonia and ammonium nitrate have been observed in the upper troposphere over the Asian monsoon region. The experiments in the cloud chamber now show that ammonia and nitric acid together with traces of sulfuric acid allow condensation nuclei to grow rapidly. “Furthermore, our measurements show that these condensation nuclei are also highly efficient ice nucleation particles whose effectiveness is comparable to that of desert dust,” explains Paul Winkler from the research group Aerosol Physics and Environmental Physics at the University of Vienna. The model calculations confirm that ammonia enters the upper atmosphere in large quantities during the Asian monsoon, where it quickly leads to the formation of the particles together with nitric acid, which is produced locally by lightning, together with traces of only sulfuric acid. As a result, the cooling temperatures in the upper troposphere result in ice particles that can spread across the northern hemisphere. “Most of the ammonia emissions in South Asia come from agriculture and here primarily from the increased use of artificial fertilizers in addition to natural fertilization with manure,” says Winkler.
Tyrolean technology pioneers
For the CLOUD experiments, the Innsbruck research group led by Armin Hänsel, in close cooperation with the spin-off company Ionicon Analytics GmbH developed special measurement methods. Hansel’s team is considered an international pioneer in the field of trace analysis, as this technical innovation from Tyrol delivers results with extremely high sensitivity in real time. The CLOUD research team consists of numerous working groups from all over Europe and North America and is financially supported by the European Union and numerous national sponsors – including the Austrian research funding agency FFG.