SciDev.Net

Pollution over Kathmandu

Flickr/Parahamsa

[KATHMANDU] Researchers have shown that pollution from China, India, Nepal and Pakistan can reach altitudes of over 5,000 metres in the Himalayas, contributing to the warming of the atmosphere and potentially affecting the South-East Asian monsoon cycle.

They also found that new aerosol particles — ultrafine particles suspended in the atmosphere — can form at these heights.

The French–Italian team, whose findings were published in Proceedings of the National Academy of Sciences this week (13 October), conducted their study over a 16-month period at the Himalayan Nepal Climate Observatory site in Nepal's Khumbu Valley, located at an altitude of 5,079 metres.

Lead author Hervé Venzac, from the Blaise Pascal University in France, and his team observed that when pollutants such as vehicle fumes transported from the plains of Nepal and other Himalayan countries meet down-sloping cleaner air from the troposphere — the lowest portion of the Earth's atmosphere — aerosol particles are formed.

Discussing the implications of the study, co-author Paolo Laj, at the Joseph Fourier University, France, told SciDev.Net, "Aerosol particles emitted by burning processes absorb sunlight, causing warming of the lower atmosphere and thus contributing to global temperature rise to the same extent as major greenhouse gases."

This atmospheric warming can have a significant effect on the South-East Asian monsoon, as the functioning of monsoon cycles relies on temperature regulation and the production of warmth in the atmosphere — if atmospheric temperatures rise or fall, these cycles could be significantly impacted.

The team's findings are expected to provide a basis for the understanding of this production of warmth and could also shed light on the melting of glaciers in the region.

"This study is remarkable as it can explain the phenomenon of the melting of glaciers that we have started to observe in the Himalayas," says Ngamindra Dahal, a hydrometeorologist at the National Trust for Nature Conservation, Nepal.

The study is the first long-term data analysis of aerosol formation at high altitudes. Additionally, it reveals that the frequency of this formation is high — similar to that reported in urban environments.

"Though further study is necessary to find out what could be the exact source of the up-sloping pollutants, this research clearly shows how pollution can affect particle formation [at high altitudes] and hence climate change and the monsoon cycle in the region," says Laj.

Link to article in Proceedings of the National Academy of Sciences