Old Version

Air Pollution

Crossing Borders

New research shows airborne pollutants are flowing from heavily populated South Asian countries to the northern side of the Himalayas, causing damage to the world’s third-largest store of ice

By NewsChina Updated Dec.28

The Nam Co atmospheric monitoring station in the Tibetan Plateau / Photo by Cong Zhiyuan

China’s air pollution problem is no secret. Nor is India’s - in fact, a Greenpeace report found that in 2015, the average Indian was exposed to more pollution than the average Chinese for the first time on record. It was believed that the towering Himalayas kept most of South Asia’s pollutants from blowing into China, but recent research shows that even Mount Everest (known as Qomolangma in Tibet) is no match for contaminated air. 

Chinese scientists have found evidence that airborne pollution, known in scientific circles as atmospheric brown clouds (ABCs), travels from South Asia toward the Himalayas, streams through mountain valleys and even flows over the mountains themselves to penetrate the Tibetan Plateau. Data taken from multiple observation stations in the region show that similar types and concentrations of pollutants exist on both the north and south sides of the world’s tallest peaks. 

Some of these airborne particles cause a net heating effect and thus contribute to global warming. Their growing presence is thought to be accelerating the thawing of snow and glaciers in the Hindu Kush, Himalayan and Tibetan regions, an area also known as the Third Pole, so named because it holds the most snow and glacial ice in the world outside of the polar regions. 

Southern Situation 
In recent years, an increasing amount of suffocating ABCs has smothered many South Asian regions, particularly in India and Nepal. According to Greenpeace, satellite-measured levels of PM2.5 - particulate matter that can penetrate the lungs and is 2.5 micrometers or smaller in diameter - rose 13 percent in India from 2010 to 2015. In comparison, China’s levels fell 17 percent during that same time period due to extensive government measures to crack down on heavy polluters.  

Another area that has been increasingly pummeled by pollution is the densely populated Indo-Gangetic Plain (IGP), a region that spans over much of eastern Pakistan, northern India and Bangladesh. Conditions worsen during the non-monsoon season, which lasts from October to May. Without the heavy rains to clear pollutants from the air, ABCs darken the sky for longer periods of time. For example, during these seasons in Kathmandu, a clear view of the Himalayas is very rare due to the pollution shrouding the valley region. These ABCs form from emissions from factories, fossil fuel combustion, biomass burning and biofuel heating. 

The rising amount of soot, sulfates and other pollutants in ABCs is posing a growing threat to Asia’s water and food security, according to a 2008 report by the United Nations Environment Program. Scientists think this increase contributes to global warming and the thawing of glaciers and snow packs in the region. Certain pollutants absorb solar radiation that would otherwise be reflected back into space, thus heating the overall surface-atmosphere system and quickening the melting of snow and glaciers. Ice core samples taken from both the southern and northern slopes of the Himalayas have shown that soot concentrations have risen significantly during the recent decades of rapid industrialization. Westerlies blow the pollution that originates in the heavily populated IGP toward the mountain range, pushing airborne pollutants into valleys and up Himalayan slopes. 

The Nam Co atmospheric monitoring station / Photo by Cong Zhiyuan

Latest Evidence 
Kang Shichang, director of the State Key Laboratory of Cryospheric Science under the Chinese Academy of Sciences (CAS), has specialized in atmospheric monitoring of the Qinghai-Tibetan Plateau for the past 15 years. His group has published more than 400 peer-reviewed papers in academic journals both in China and abroad. Kang’s work has been instrumental in proving this case of transboundary pollution, or pollution that spans across multiple countries. 

Kang spoke to NewsChina about the data that linked pollution from South Asia to that observed on the northern side of the Himalayas. In April, scientists at Qomolangma (Everest) Station, a CAS atmospheric monitoring site at Mount Everest’s northern base, noticed a sudden surge in black carbon levels. Typically, the Everest station records black carbon concentrations of about 0.3 micrograms per cubic meter, but levels spiked to 1.2-2.4 micrograms per cubic meter from April 9 to 18. (While severe for this unpopulated area, this amount is still relatively low for China; in the country’s urban areas, black carbon concentrations tend to range from 6-11 micrograms per cubic meter, according to a 2012 report by the United States Environmental Protection Agency.) According to Kang, the extremely high black carbon content recorded during this time differed so significantly from baseline data that it can be considered a “pollution event.” Considering the limited sources of pollution in the immediate area, Kang hypothesized that the black carbon upsurge was caused by transboundary pollution from South Asia.  

Kang and his research team analyzed the airflow with the help of satellite images, computer simulations and meteorological data. They concluded that 97 percent of the air masses that passed over the station during that period came from across the border. “The masses of air passed over most of Nepal before finally climbing over the Himalayas to reach the northern slope of Mount Everest,” read a report by Kang and his team.  

They sourced the pollution based on levels of aerosol optical depth (AOD) ascertained from NASA satellite images. AOD is a measure of how much sunlight is blocked by aerosol particles, or airborne matter like dust and pollutants. According to the US National Oceanic and Atmospheric Administration, an AOD of 0.01 corresponds to a very clear atmosphere, while a 0.4 equates to a hazy one. Kang and his team found the major transboundary pollution source was Nepal, the AOD of which exceeded 0.6 throughout this stretch, while the secondary source was northern India. They deduced that a rise in the AOD measurement taken at the Everest station stemmed from an increase of fine particles from biomass burning, such as the burning of wood in cooking stoves or forest fires. Pinpointing the pollution’s cause then became easy. In early to mid-April, wildfires ravaged more than 3.2 million acres of Nepalese forests. Based on Kang’s data, the haze that resulted from the flames seems to have made its way to Everest’s northern slope. 

An aeiral view of the ABC outburst caused by forest fires in south Asia, April 2016 /

Widespread Effect 
Mount Everest is not the only point at which aerosol particles have crossed China’s border. CAS’s Nam Co Station, located in central Tibet about 800 kilometers northeast of the Qomolangma Station, observed an unusual upswing in AOD levels in March 2009. Nam Co typically records AOD values of 0.03, but its number on March 16 of that year was 0.42, a level similar to that of Beijing’s urban center.  

Kang’s team published a paper on this event in the journal Atmospheric Chemistry and Physics in mid-2015. The team’s report detailed “how polluted air masses from an [ABC] over South Asia reach the Tibetan Plateau within a few days.” It said that the black carbon within ABCs are known “to exert a great melting potential” on glaciers and snow packs. 

While this particular paper focused on the March 2009 pollution event, Kang said that it is likely airborne pollution is crossing into the Third Pole frequently every year during the pre-monsoon season of March through May, as “that is the same period during which ABCs normally break out.” He concluded this based on nearly a decade of observations.  

Collective Problem 
“The Himalayas are not an impermeable barrier,” said atmospheric scientist Arnico Panday in an email interview with NewsChina. He is the program coordinator of the International Center for Integrated Mountain Development’s (ICIMOD) Atmosphere Initiative and a former visiting professor of one of his alma maters, MIT. “There are passes and river valleys that cross the Himalayas at numerous places, so it is easy for air from the south side to reach the north side,” he added. 

Kang emphasized the importance of regional cooperation among the countries involved in finding a solution to long-range transboundary air pollution issues in the Himalayan regions. But so far, the first regional agreement to tackle this issue in South Asia, 1998’s Malé Declaration on Control and Prevention of Air Pollution and its Likely Transboundary Effects for South Asia, has yet to produce results. “Right now most people in the source regions don’t even know the consequences of the pollution they are emitting,” Panday said. He explained that there is still a lot of research to be done to fill the sizable gaps in the scientific understanding of the relationship between source regions and the locations of impacted areas.  

South Asia is not the only region that has been afflicted by pollution that crosses borders. To combat the negative impact of Continental Europe’s sulfur emissions on Scandinavian lakes, the European community signed the Geneva Convention on Long-range Transboundary Air Pollution in 1979. Pollution from illegally set forest fires in Indonesia shrouded much of Southeast Asia in a haze in September 2015. Airborne pollutants from China’s densely populated east coast have been known to ride the westerlies to South Korea and Japan.  

In comparison to these other cases, the amount of pollution crossing from the south side of the Himalayas to the north is less significant. However, its impact may be colossal, as it accelerates the melting of the snow and glaciers that anchor some of Asia’s largest rivers - the Yangtze, Yellow, Mekong and Ganges - which together support more than two billion people.  

“We [in China] are planning to deepen our cooperation with ICIMOD and enhance joint atmospheric observations on the Third Pole,” Kang said. “We also expect to include Indian researchers’ efforts into our network on the transboundary air pollution issue.” 
He stressed that working together on technological research and information exchange will be an indispensable part of controlling the glacier thaw and the development of ABCs. If the pollution continues unrestrained, no country in the area will be safe from the effects of the inevitable environmental damage.