For those of us living in developed countries it is common to be surrounded by imported goods. The car parked outside your house, your laptop, camera and smartphone, the food you are preparing for dinner, and even the chair you are sitting on may well have originated many hundreds of miles away. Some of those goods will have been produced responsibly, whilst others will have added to the choking smogs that frequent cities like Tianjin in China.

Although it has long been known that high-income countries are responsible for a significant share of the pollution burden in developing countries, it has always been hard to map out exactly where air pollution is being exported to. To resolve this, Daniel Moran from the Norwegian University of Science and Technology and Keiichiro Kanemoto from Shinshu University in Japan used air pollution maps and trade databases from 187 countries to model the link between severe air pollution hotspots and global supply chains. In particular they modelled the spatial patterns of sulphur dioxide, nitrogen oxides and PM10 particles, and assessed how these had changed over time.

The results clearly show that the US and European countries have achieved impressive emissions reductions at home, but at the same time have significantly increased their pollution footprint abroad. "We anticipated this spatial spread, but the volume of emissions exported was far higher than we had expected," said Kanemoto, whose findings are published in Environmental Research Letters (ERL).

Perhaps not surprisingly, the team found that China bears the greatest pollution burden for other countries, with India not far behind. Meanwhile, the US and countries across Europe are guilty of offloading some of the largest pollution burdens onto others. "The UK, for example, has increased imports from China and other countries to satisfy its consumption," said Kanemoto. "This alleviates the UK's domestic air pollution but drives growth in global air pollution."

Over time, the rapid growth in consumption in developed countries appears to have massively increased their air pollution footprints. For example, Kanemoto and Moran show that in 1970, 90% of the US sulphur dioxide footprint rested in just 1.5% of global land area. By 2008 the footprint extent had doubled to 3.1% of global land area. The equivalent NOx footprint growth for the US has been even more dramatic, rising from 0.6% to 3.6% of global land area over the same time period, and PM10 worse still, growing 15-fold to 9.9% of global land area by 2008.

But the new pollution export maps could help to identity the most effective abatement opportunities and focus clean-up efforts. Kanemoto and Moran show that if the US targeted clean-up in the 1% of land area where its air pollution footprint falls most heavily, those efforts could reach 80% of its sulphur dioxide and NOx footprints, and 55% of its PM10 footprint.

"We hope that identifying hotspots linked to trade will help and encourage the down-stream users – companies, countries and individuals – to participate in clean-up measures at those hotspots," said Kanemoto.

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