PICTURE: Untouched places like the HIMALAYAS are useful when trying to understand the natural atmospheric conditions before industrialization. Show more CREDIT: FEDERICO BIANCHI
In the valleys of the Himalayas, naturally emitted gases can form large quantities of new particles, which can be transported to great heights by the mountain winds and injected into the upper atmosphere.
The emitted particles can ultimately affect the climate by acting as nuclei for cloud condensation. These new insights into particle formation and sources will contribute to a better understanding of past and future climates.
“In order to understand how the climate has changed in the last century, we need to know the natural atmospheric conditions before industrialization as reliably as possible,” says Associate Professor Federico Bianchi from the Institute for Atmospheric and Earth System Research at the University of Helsinki (INAR).
To this end, scientists are looking for pristine places around the world where human influence is minimal. An international group of researchers has now completed a comprehensive study at the Nepal Climate Observatory in the Pyramid Station, which is located near the Everest base camp at 5050 m above sea level. There they could study the formation of atmospheric particles that were far removed from human activity. The results were published today in the prestigious journal Nature Geoscience.
Particles of natural origin
The study shows that winds in the valley bring vapors emitted by the vegetation at the foot of the Himalayas to higher altitudes. During this transport, these gases are converted by photochemical reactions into compounds with very low volatility, which quickly form large numbers of new aerosol particles. These are then transported into the free troposphere, a region of the atmosphere with very little human influence.
"You can think of the entire Himalayas as an aerosol factory that continuously produces a large amount of particles and then injects them directly high into the atmosphere above Everest," says Bianchi. From these measurements we calculate that the transport of particles can increase today's particle concentration over the Himalayas by a factor of up to two or more.
It is the first time that scientists have considered mountain ventilation as a major potential source of atmospheric particles in the free troposphere.
In addition, the freshly formed particles have a natural origin, with little evidence of the involvement of anthropogenic pollutants. This process is therefore likely to have remained essentially unchanged since the pre-industrial era and could have been one of the main sources that contributed to the aerosol population in the upper atmosphere during this period. These new observations are therefore important in order to better estimate the pre-industrial baseline aerosol concentrations in this large region. The inclusion of such processes in climate models can improve the understanding of climate change and the prediction of future climate.
Future studies should focus on a better quantification of this phenomenon and examine it in other high mountain regions as well.
Federico Bianchi, Heikki Junninen, Alessandro Bigi, Victoria A. Sinclair, Lubna Dada, Cristopher R. Hoyle, Qiaozhi Zha, Lei Yao, Lauri R. Ahonen, Paolo Bonasoni, Stephany Buenrostro Mazon, Manuel Hutterli, Paolo Laj, Katrianne Lehtipalo, Juha Kangasluoma1, Veli-Matti Kerminen, Jenni Kontkanen, Angela Marinoni, Sander Mirme, Ugo Molteni, Tuukka Petäjä, Matthieu Riva, Clemence Rose, Karine Sellegri, Chao Yan, Douglas R. Worsnop, Markku Kulmala, Urs Baltensperger and Josef Dommen. Biogenic particles formed in the Himalayas are an important source of free tropospheric aerosols. Natural Geosciences, December 2020.