By Lily Hess
In recent years, ozone pollution has caused an annual loss of USD 63 billion in wheat, rice and maize harvests across East Asia, according to a study recently published in Nature Food. The region has become a global hotspot of air pollution in recent decades.
China alone loses a third of its wheat, nearly a quarter of its rice and 9 percent of its maize due to ozone pollution, translating into annual harvest losses of USD 21.8 billion, 30.8 billion and 7.8 billion respectively.
Most of the world’s ozone exists in the stratosphere as the ozone layer, where it protects the Earth from a vast majority of the sun’s ultraviolet light and the potential damage this radiation could cause. It is in the troposphere – the lowest level of the atmosphere – where ozone can become a pollutant. Here, fossil fuel emissions mix with sunlight to create ozone, a major component of smog that is particularly prevalent during the summer.
Although ozone pollution levels have stagnated or declined in North America and Europe over the last two decades, they have been rising in East Asia. Industrializing economies, urbanizing populations and growing transportation sectors have all contributed to a steep rise in energy use that still largely comes from burning fossil fuels.
The region is also a center of economic activity that depends heavily on burning fossil fuel. East Asia is a major manufacturing hub; China in particular produced more than 28 percent of the world’s manufactured goods in 2018. Eight of the world’s 10 largest ports by volume of shipped goods are also located in the region.
At the same time, East Asia is also an important center for agriculture, with the three countries studied by the researchers – China, Japan and South Korea – producing roughly 43 percent of the world’s rice, 22 percent of its wheat and 29 percent of its maize in 2020, according to the Food and Agriculture Organization of the UN.
“A problem with the ozone impacts on cereal crops is that [farmers] will never know that the yield was reduced by ozone,” said Kazuhiko Kobayashi, a professor at the University of Tokyo and an author of the study, in an email. “There are no visible damages in leaves identifiable as caused by ozone.” He also noted that ozone damage happens across entire regions, so crop losses due to ozone pollution may be more difficult to identify within individual farms.
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