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Air-polluting chemicals travel across continents, pose greater risk of cancer: study(downtoearth,)

Some pollutants travel much farther than what earlier global climate models had predicted. According to findings, published in the Proceedings of the National Academy of Sciences Early Edition online, organic aerosols can amplify global human exposure to toxic particles by proving a shield. Hence, pollutants last longer in the atmosphere, which means global lung cancer risk from a pollutant caused by combustion is much higher than estimated earlier.

The study was done by scientists at Oregon State University (OSU), the Department of Energy’s Pacific Northwest National Laboratory (PNNL) and Peking University.

"This work brings together theory, lab experiments and field observations to show how viscous organic aerosols can largely elevate global human exposure to toxic particles, by shielding them from chemical degradation in the atmosphere," said PNNL climate scientist and lead author Manish Shrivastava.

Pollutants released during fossil fuel burning, forest fires and bio-fuel consumption include air-polluting chemicals known as polycyclic aromatic hydrocarbons (PAHs). The Environmental Protection Agency (EPA) in the US has identified some PAHs as cancer-causing agents.

Understanding of aerosols

Researchers had long believed that PAHs can move freely within the organic coating of aerosols—tiny airborne particles that form clouds, cause precipitation and reduce air quality. But this understanding of aerosols has changed over the last few years.

Recent experiments led by the PNNL co-author Alla Zelenyuk revealed that the aerosol coatings can be quite thick depending on the conditions. In a cool and dry atmosphere, the coating can become as thick as tar, trapping PAHs and other chemicals. By restricting their movement, the coating protects the PAHs from degradation.

To analyse how far the protected PAHs could travel, the researchers studied both old and new models. When the new model's numbers were measured at the top of Mount Bachelor in the central Oregon Cascade Range, the level of PAH concentrations was observed to be far higher.

“The level of PAHs we measured on Mount Bachelor was four times higher than previous models had predicted, and there’s evidence the aerosols came all the way from the other side of the Pacific Ocean,” said Staci Simonich, a toxicologist and chemist with the College of Agricultural Sciences and College of Science at OSU.

As opposed to earlier predictions

Globally, the previous model predicted that exposure to PAH could cause half a cancer death out of every 100,000 people. But the new study showed that shielded PAHs travel great distances and cause global risk of two cancer deaths (four times) per 100,000 people. It exceeds World Health Organization (WHO) standards.

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