The nanoparticles released into the atmosphere by human activities would contribute to intensifying water extremes (heavy rainfall and droughts). At least that’s what a study recently published in the journal Scientific Reports suggests. Also, the authors call for a better consideration of these compounds in the dynamics of the water cycle.
While air quality has generally improved in Western countries in recent decades, the situation is different for ultrafine particles, also called nanoparticles because of their size, which ranges from 1 to 100 nanometers. However, this dust invisible to the naked eye from the combustion of fossil resources would play an important and hitherto underestimated role in the evolution of climatic extremes.
An alteration of the hydrological cycle at the regional level
Recent measurements taken by aircraft at several points around the globe suggest that by altering cloud microphysics, ultrafine particles amplify both extreme precipitation and drought events. Indeed, by acting as condensation nuclei, they multiply the number of cloud droplets and reduce their size. At first, the formation of precipitation is delayed and the water struggles to fall. However, by erecting a larger reservoir of latent energy, this dynamic subsequently leads to potentially more intense precipitation.
This is at least the theory put forward by the researchers in their paper. “With conventional models of cloud formation, we can show that the increase in ultrafine particles also leads to the formation of particularly fine droplets,” says Junkermann, lead author of the study. “A heterogeneous distribution of nanoparticle pollution could explain the large regional differences in the evolution of extreme weather events.”
The importance of taking nanoparticles into account
In some areas, the air concentration of nanoparticles has increased nearly 150 times. “These extreme concentrations have been attributed to power plants, refineries or shipping traffic and, often, especially to large incineration plants” , reports the researcher. Indeed, the use of ammonia in order to limit nitrogen oxide emissions has been accompanied by a significant increase in nanoparticle emissions. If the lack of observations makes it difficult to assess the impacts, this growth obviously affects the dynamics of the hydrological cycle.
“Above the Mediterranean Sea, for example, the concentration of particles has increased 25 times since the 1970s,” says the lead author of the study. “Over the same period, strong variations in precipitation can be observed with a decrease in average precipitation and an increase in drought and extreme events”.
