How monsoon winds affect climate change by transporting pollutants to the upper atmosphere
While the Asian monsoon brings rain that is vital to the agricultural economy of the vast region, it is also known to soak up chemical pollutants in the upper atmosphere that accelerate climate change.
Scientists eagerly await the results of a US-led international project reviewing previous findings, published in Science that pollutants generated by human activity are transported upward through the monsoon system and affect atmospheric chemistry and in turn alter the climate.
Atmospheric chemistry is the study of the components of planetary atmospheres, including the troposphere – the layer of the atmosphere closest to Earth – the stratosphere and other upper layers of the atmosphere.
Laura Pan is the project’s principal investigator and a scientist at the US National Center for Atmospheric Research, which co-leads the Asian Summer Monsoon Chemical and Climate Impact Project (ACCLIP) with the National Aeronautics and Space Administration (NASA).
ACCLIP investigates how gas and aerosol emissions affect global chemistry and climate.
“In recent decades, satellites have revealed that the monsoon creates a distinct layer of chemicals about 10 miles (16 kilometers) above Earth, but we know very little about its composition and evolution,” Pan told SciDev.Net.
“ACCLIP gives us the chance to taste what’s out there, but we know that regardless of its composition, it’s related to the climate.”
Studying the sky
The month-long project will involve scientists from Korea, Japan, Italy and Germany, who will focus on the monsoon’s vigorous circulation and sample the chemical pollutants that are drawn up into the upper atmosphere where they are absorbed in various ways. rainfall over Asia. for both floods and droughts.
Researchers, using aircraft based at the US Air Force base in South Korea, will fly through areas of the worst air quality — where the Asian monsoon occurs. Scientists believe that as the rain flows down, a wide variety of chemical pollutants are sucked into the upper atmosphere by wind systems and that their reactions are linked to climate change.
Evidence that the South Asian monsoon transports pollutants as high as the stratosphere was first available in 2015 when a similar experiment, using research aircraft flying over pollution hotspots, was conducted by the Germany-based Max Planck Institute for Chemistry, the Karlsruhe Institute of Technology and the German Space Center.
The lifted air contains various chemicals and aerosols produced by industry, agriculture, vehicle emissions and other human activities, along with natural biological processes.
“Research conducted to date shows that the Asian summer monsoon lifts pollutant gases and aerosols from the boundary layer of Asia to the upper atmosphere. Some of these pollutants get higher in the stratosphere and horizontally to the western Pacific and West Africa in the form of vortices,” Suvarna Fadnavis, of the Indian Institute of Tropical Meteorology in Pune, told SciDev.Net.
“These polluting gases and aerosols affect the radiation balance and chemical composition of the upper troposphere and the lower stratosphere (upper atmosphere).”
Lockdowns during the COVID-19 pandemic temporarily halted industrial and road traffic, reducing pollutant production and impacting monsoons, according to a 2021 Letters for environmental research study. Researchers found that rainfall was increasing in South Asia, which has faced water scarcity in recent decades.
According to a report by the UN Intergovernmental Panel on Climate Change (IPCC).
“Scientists are interested in knowing if the pollutants on the surface reach the stratosphere during the surge that occurs during the monsoon and this project could be helpful,” said Jayaraman Srinivasan, a leading scientist at the Divecha Center for Climate Change and an honorary professor at the Indian Institute of Science, Bangalore’s Center for Atmospheric and Oceanic Sciences.
Fadnavis says the ACCLIP project could help understand the “links of the unknown pattern of the Asian summer monsoon to chemical changes occurring at higher elevations over the Asia-Pacific region and the implications for monsoon rainfall, extreme or drought conditions, ice clouds, temperature changes, etc.”
Jayanarayanan Kuttippurath, a climate scientist at the Center for Oceans, Rivers, Atmosphere and Land Sciences, Indian Institute of Technology, Kharagpur, says wind systems that transport pollutants and moisture are a concern for East Asian and South Asian countries.
“This is especially important for regions like the Indo-Gangetic Plain, where air pollution is very high – the urban regions are already big heat islands and additional warming would make life in the cities more miserable,” he says.
Recent studies identified an area of high aerosol load near the tropopause – the boundary between the troposphere and the stratosphere – called the Asian tropopause aerosol layer. This also serves to move aerosols to the upper atmospheric layers, where high aerosol concentrations can affect “radiative forcing” and cool the Earth’s surface.
Radiative forcing is a measure of the change in the energy balance in the atmosphere that results from a “forcing agent” – such as greenhouse gases and aerosols.
The Asian Summer Monsoon Chemical and Climate Impact Project is studying the outflow — the wind generated by a storm — from the Asian monsoon circulation, which occurs primarily in the upper troposphere and stratosphere, said Kenneth Jucks, manager of the Upper Atmosphere Research Program at NASA .
“Since we’re looking at the outflow, it’s ideal to be deployed on the coast of Asia to observe across the Pacific,” Jucks said. “The outflow is influenced by processes occurring in much of Asia, including China, the Himalayas, northern India and even Southeast Asia.”
Kuttippurath says reliable measurements of the upper troposphere and lower stratosphere are difficult to obtain, adding that “this type of campaign would certainly help scientists better understand the region’s chemistry and dynamics.”
High-altitude research plane explores the upper levels of the Asian monsoon
J. Lelieveld et al, The South Asian monsoon-pollution pump and purifier, Science (2018). DOI: 10.1126/science.aar2501
Suvarna Fadnavis et al, The impact of COVID-19 lockdown measures on the Indian summer monsoon, Letters for environmental research (2021). DOI: 10.1088/1748-9326/ac109c
J.-P. Vernier et al, CALIPSO detection of an Asian tropopause aerosol layer, Geophysical Survey Letters (2011). DOI: 10.1029/2010GL046614
Pengfei Yu et al, Radiative forcing by anthropogenic sulfur and organic emissions reaching the stratosphere, Geophysical Survey Letters (2016). DOI: 10.1002/2016GL070153
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