The US and China trade pollution as well as goods (Image: Darley Shen/Reuters)

What goes around comes around – quite literally in the case of smog. The US has outsourced many of its production lines to China and, in return, global winds are exporting the Chinese factories’ pollution right back to the US.

Decades ago, the US began outsourcing its industrial production, resulting in the ubiquitous “made in China” label. US factories shut down and Chinese ones opened up in droves. It looked like a clever scheme to shift noxious pollution to the opposite side of the planet, but it is backfiring.

Jintai Lin of Peking University in Beijing, China, and his colleagues used economic and emission data to divide Chinese emissions into several categories. They measured emissions produced in China for products consumed in China, and emissions produced in China for products destined for the US.


Unwelcome export

The team focused on particulate emissions – tiny specks of pollutants like sulphates and soot that make up smog and are harmful to human health. Sulphate causes respiratory disease and is particularly problematic for the young, the elderly and people with asthma. areas a result acceptable levels of sulphate in the air are strictly controlled in many countries including the US.

The team found that between 17 and 36 per cent of smog produced in China in 2006 came from factories making goods for export. One-fifth of those goods are destined for the US.

An added twist came when the team combined their emissions data with atmospheric models that predict how winds shuttle particles around. These winds push Chinese smog over the Pacific and dump it on the western US, from Seattle to southern California.

The modelling revealed that on any given day in 2006, goods made in China for the US market accounted for up to a quarter of the sulphate smog over the western US.

Smog consumption

It is well known that much of the carbon dioxide produced by Chinese factories can be attributed to US goods, implying that the US is partially responsible for China’s growing greenhouse gas emissions. But no one had yet looked at smog.

People in the US and other rich, industrialised countries consume more resources than the global average, says Lin’s collaborator Dabo Guan of the University of Leeds in the UK, so they are responsible for a larger proportion of global pollution emissions. “Emissions can only be effectively mitigated if our lifestyle in the West can be transformed to a sustainable level.”

But although it is easy to blame countries like the US for outsourcing their factories, China does benefit economically, says team member Steven Davis of the University of California at Irvine. “Both consumers and producers benefit,” he says. “Producers have a market for their goods and consumers have affordable goods.”

“Trade is for mutual benefits,” agrees Haibing Ma of the Worldwatch Institute, a non-governmental research body in Washington DC. He says China has been increasing the efficiency of its production chain and producing more while using less energy, particularly since 2005. That should help stem the smog that is once again choking major Chinese cities.

Journal reference: PNAS, DOI: 10.1073/pnas.1312860111