Rising levels of ground-level ozone in China and nearby countries are having a big effect on the yields of staple crops such as wheat, rice and maize

Increasing concentrations of ground-level ozone in East Asia are causing ever more damage to crops. The relative fall in yields of wheat, rice and maize in China, Japan and South Korea is costing $63 billion a year, according to Zhaozhong Feng at the Nanjing University of Information Science and Technology in China and his colleagues.

Surface ozone concentrations in China have been rising by around 5 per cent a year, says Feng. “Such a fast increase of surface ozone has increased the ozone threat to crop yields,” he says.

Ozone is a highly reactive gas. Its presence in the stratosphere is beneficial as it blocks dangerous ultraviolet light, but ground-level ozone harms plants and animals.

Surface ozone forms when nitrogen oxides (NOx) react with volatile organic compounds in the presence of sunlight. Surface ozone levels have increased in many regions worldwide because of NOx pollution, mainly from vehicles. Crop yields have also generally risen due to improved methods and varieties, but they would be even higher without ozone.

Based on measurements from 3000 sites in China, Japan and South Korea, Feng’s team estimates that ozone pollution is causing relative yield losses of 33 per cent for wheat, 23 per cent for rice and 9 per cent for maize.

This is nearly double estimates from 2016. The increase is partly because ozone levels are now higher and partly because the researchers calculate that ozone does more damage than previously thought, says Feng.

The estimate of $63 billion-worth of crop losses is plausible, says Nigel Bell at Imperial College London. The huge impact of surface ozone has slowly been becoming clear, he says. “It’s something that gradually crept up on us.”

Because farming is one of the biggest sources of greenhouse gas emissions and continued land clearance for farms is causing habitat loss, the findings mean that ozone pollution is also indirectly leading to global warming and biodiversity loss. But the relationship between ozone and other air pollutants is complex, making it hard to tackle the problem in the short term.

One of the reasons ozone levels are rising in China is due to falling levels of particulate pollution, says Feng. Particulates reduce ozone by blocking sunlight and by inhibiting the chemical reactions that produce the gas.

What’s more, very high levels of nitrogen oxides consume ozone, says Feng, so reducing NOx pollution can increase ozone levels. “These processes together contribute to the fast increase of surface ozone in China,” he says.

Journal reference: Nature Food, DOI: 10.1038/s43016-021-00422-6

Ozone pollution: Gas causes $63 billion damage per year to East Asian crops | New Scientist