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 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 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.

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The ozone layer may recover more quickly than first thought, thanks mostly to reduced emissions from China of a banned ozone-depleting gas.

Luke Western at the University of Bristol, UK, and his colleagues analysed data on atmospheric levels of the banned ozone-depleting gas trichlorofluoromethane, or CFC-11, and found that emissions from eastern China declined after 2017. Emissions in 2019 were 10,000 tonnes less than the average annual emissions between 2014 and 2017, says Western.

Another study, led by Steve Montzka at the National Oceanic and Atmospheric Administration in Colorado, which estimated global CFC-11 emissions, also found a decline worldwide in 2019 – a trend that seems to be continuing. “Initial concentration trends in 2020 look similar to those in 2019,” says Montzka.

The decline in CFC-11 emissions from eastern China accounts for around 60 per cent of this recent worldwide decline, says Western.

The hole in the ozone layer above Antarctica has been healing in recent years largely because of the Montreal Protocol agreed internationally in 1987, which banned the production of ozone-depleting substances including CFC-11. But studies in 2018 and 2019 indicated that full recovery of the ozone layer was likely to be delayed, because of illegal production of CFC-11 in China between 2014 and 2017. The reduced emissions from China since 2017 mean this feared delay could now be avoided, say both Montzka and Western.

“If the new emissions had continued at the levels we saw in 2014 to 2017, we could have seen ozone recovery, back to 1980 levels, delayed by a few years,” says Western. “As it stands, we hope that we have avoided any substantial delay to ozone recovery.”

“It’s pleasing to see that the mechanisms of the Montreal Protocol – combining the knowledge of scientists, industry experts, policy makers and national authorities – enabled a rapid and effective response to its first major violation,” says Western.

Craig Poku at the University of Leeds, UK, says the trends displayed in emissions from eastern China are promising but continued monitoring will be critical. “I would say that it’s too early to say that delays in [ozone] recovery will not happen based on the data shown,” he says.

Journal references: Nature, and

The recovery of the ozone hole over Antarctica is likely to be delayed by the illegal production of an ozone-destroying gas in China, according to the first assessment of the banned chemical’s impact.

In the worst case, the recovery will be delayed by around 18 years if production of trichlorofluoromethane (CFC-11), used to make foam insulation in fridges, continues unabated. But such an extreme scenario is seen as unlikely because of signs Chinese authorities have begun cracking down on the problem.

If production of the gas is phased out over the next decade, which seems more likely, the result would be a two-year delay in the ozone hole’s recovery, says Martyn Chipperfield at the University of Leeds, UK. Were production to stop immediately, there will be virtually no impact on its recovery, according to modelling by his team.

That is because the increase in CFC-11 emissions took place between 2013 and 2017, which was noticeable but not enough to have a large impact among all the other factors that affect ozone recovery. The ozone hole, which is usually open between September and November, .

“We can get things back on track quite quickly. The implications for the ozone layer need not be too damaging,” says Chipperfield.

The new research follows scientists that CFC-11 levels in the atmosphere were rising, despite their production being banned internationally in 2010 under the Montreal Protocol. Researchers later pinpointed the source as the eastern China provinces of Shandong and Hebei, where it is believed CFC-11 has been illegally used to make foam.

Clare Perry at the Environmental Investigation Agency says that due to the response from China and the international community, “it’s highly unlikely that illegal CFC-11 production will continue at the same level in China, and therefore the 18-year delay is very unlikely”.

It seems CFC-11 emissions have already begun declining this year, according to preliminary findings by Stephen Montzka at the National Oceanic and Atmospheric Administration in Colorado, which were presented last month at a meeting of the parties to the Montreal Protocol in Italy.

“This current event, provided action is taken quickly, shouldn’t have too much of a long-term impact. That’s not to say we should get complacent,” says Matt Rigby at the University of Bristol, UK.

Chipperfield says it is important to keep an eye on a group of ozone-depleting chemicals known as very short-lived substances, which aren’t covered by the Montreal Protocol.

“Despite all the problems, there is remarkable optimism that the message is getting through”