Ozone pollution is reducing wheat yields in China by one-third and significantly cutting the productivity of other staple crops, as the country’s ground-level ozone levels continue to rise despite improved air quality, according to a new study published Monday in the journal Nature Food.

Using surface ozone concentration data between 2017 and 2019, an international team led by researchers from the Nanjing University of Information Science and Technology estimated that the air pollutant has decreased wheat yields in China by nearly 33%. The study also found that high-yield hybrid rice varieties — which account for nearly half of the country’s rice production — were more sensitive to ozone pollution, losing about 30% of their output compared with 12% seen in regular rice plants.

Researchers also found ozone pollution affected crop growth and production in other East Asian countries, including Japan and South Korea.

China is one of the global hotspots for ozone pollution, with its ozone concentrations particularly high around the North China Plain. The region covers parts of seven provinces, including large wheat-producing provinces such as Henan and Shandong in the central and eastern parts of the country, respectively.

Feng Zhaozhong, lead author of the study, told Sixth Tone that hybrid rice varieties produce higher yields by exchanging more gasses with the environment and have a higher rate of photosynthesis, hence allowing more ozone to be absorbed by the plants and resulting in higher output loss.

“China’s crop yields have been steadily increasing, mostly because we have modern agriculture methods like fertilizers and better irrigation,” said Feng, an ecologist at the Nanjing University of Information Science and Technology. “But limiting ozone concentrations would further increase crop yields.”

Researchers calculated that if China’s ground-level ozone concentration were cut by half, the country could produce 20% more wheat and 10% more rice. They estimated that ozone pollution between 2017 and 2019 has cost China $52 billion annually in lost wheat and rice yields.

Ground-level ozone forms when nitrogen oxides — mainly from burning fossil fuels — react with volatile organic compounds in the presence of sunlight. While China has implemented measures to reduce such air pollutants, the country’s ground-level ozone concentrations have continued to rise.

Feng said ozone reduction is difficult because of the gas’ complex relationship with other pollutants. For example, reducing nitrogen oxides could lead to increased ozone levels, and improved air quality that makes way for more sunny days could in fact further increase ozone pollution.

“The Chinese government is already working on a systematic plan to reduce surface ozone concentrations,” Feng said. “Meanwhile, climate change is already happening, so we need mitigation measures, such as chemicals that could help plants block ozone.”

Editor: Bibek Bhandari.

(Header image: People Visual)