Chinese researchers are pointing to south Asia, India in particular, and biomass burning in the region as contributing to the pollution of the icy Tibetan plateau and the melting of snow there.
The brownish haze of pollution from forest fires, crop burning and domestic cooking stoves in south Asia can rise over the Himalayas to settle on the plateau, they report.
The pollutants, sulfate ions and organic compounds clearly traced to biomass burning in stoves and forest fires, were highest at times when Nasa satellites also recorded these events in south Asia.
"Many people assume that pollutants piling up on the southern slope of the Himalayas would not go anywhere because the mountains are simply too high," says Cong Zhiyuan, an environmental scientist at the Chinese Academy of Sciences' Institute of Tibetan Plateau Research in Beijing.
Ice-core samples taken from the southeastern Tibetan Plateau show rising soot concentrations during times of rapid industrial growth in India, says the report bound to generate controversy.
Cong and his colleagues have shown in two studies that the Himalayas do not block pollutants from the south. They found similar types and concentrations of pollutants on both the south and north sides of Mount Everest.
How much of the pollutants can be traced to south Asian sources is still not known, but the research establishes a strong link to biomass burning.
"The results are interesting but need further work to demonstrate that pollutants from India are reaching the Everest. The Himalayas are not a solid barrier. There are many valleys through which polluted air from Nepal can reach Everest and Tibet. To demonstrate that pollution from India reaches the Everest will require more work," J Srinivasan, chairman, Divecha Centre for Climate Change at the Indian Institute of Science told IBTimes UK.
For one, the researchers do not know to what extent the trans-Himalayan pollutants contribute to the total load of soot and other carbon-containing combustion products dumped on the Tibetan Plateau.
Veerabhadran Ramanathan, an atmospheric scientist at the Scripps Institution of Oceanography in La Jolla, California agrees the finding is compelling on the role of biomass burning, but points out that pollutants might be blown from eastern China or come from biomass burning elsewhere on the plateau.
Cong insists there is little biomass burning on the plateau and the prevailing winds tend to blow from the south and west, not eastern China.
Cong's team took weekly measurements from August 2009 to July 2010 at the Qomolangma (Mount Everest) Station for Atmospheric and Environmental Observation and Research, on the northern slope of Everest.
The concentrations and chemical components of pollutants were similar to that recorded on the southern side of the mountain, at the Nepal Climate Observatory at Pyramid Station.
A study published last year had shown that anthropogenic emissions from residential and industrial sectors contributed 70% to the black carbon concentrations in South Asia, while biomass burning accounted for 28% only.
The study also showed that regional-scale transport of these anthropogenic emissions contributed up to 30% of black carbon concentrations in western and eastern India.
A Stanford study concluded that the black and brown carbon, released in biomass burning, cause much more global warming per unit weight than carbon dioxide, besides causing the premature deaths of about 250,000 people each year.