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Ground-level ozone can reduce rice, wheat, and maize yields across East Asia. A 2022 regional study estimated substantial losses in China, Japan, and South Korea; a separate 2025 analysis estimated China-specific impacts using a different period and method. These figures describe modeled yield effects, not grain directly counted as missing from a particular harvest.
How ozone pollution affects cereal crops
The concern is ground-level ozone—ozone in the air near crops, not the protective ozone layer high in the atmosphere. Exposure during crop growth can injure plants and reduce yields. The East Asia studies estimate that effect by relating ozone exposure to crop responses and applying those relationships to monitoring or modeled exposure and crop data.
That approach can estimate regional risk, but it is not the same as measuring the amount of grain lost in every field. Results depend on the crop, growing season, cultivar, exposure metric, response relationship, and geographic detail used.
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What the studies estimate
Three-country East Asia assessment
Feng et al.’s 2022 study combined ozone-elevation experiments conducted in Asia with monitoring at about 3,000 locations in China, Japan, and South Korea. For China, it estimated relative yield losses of 33% for wheat, 23% for rice, and 9% for maize. These are study estimates, not a claim that every farm or year experiences those losses.
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The same study estimated US$63 billion in annual ozone-induced crop production losses across its assessed crops in China, Japan, and South Korea. This is an economic estimate for the study’s scope, not an audited total for a current year. The authors also reported greater estimated relative yield loss for hybrid than inbred rice.
Newer China-wide analysis
Liu et al.’s 2025 study examined China using high-resolution hourly surface-ozone data at 0.1-degree resolution for 2005–2020. It accumulated exposure above a 40 parts-per-billion threshold using AOT40, a measure of cumulative ozone exposure. The study reports that AOT40 increased 10% during 2005–2019, then decreased 5.56% in 2020; its analysis associates the 2020 decrease with COVID-19 lockdown conditions.
For China, the paper estimates relative yield impacts of 14.51% ± 0.43% for wheat, 11.10% ± 0.6% for rice, and 3.99% ± 0.11% for maize. These figures belong to that study’s analysis and should not be treated as constants that apply to all locations or years.
Regional examples within China
More localized studies show how estimates vary with place, crop, and method:
- A Yangtze River Delta analysis covering 2014–2019 used observations from 158 stations and production records from 193 districts and counties. It estimated relative losses of 4.9%–11.4% for rice and 9.4%–19.3% for wheat in that region.
- A southern China study covering 2013–2019 estimated losses of 4.0%–6.6% for double-early rice and 6.3%–11.1% for double-late rice. These estimates apply to those rice cycles and that region, not to all rice production.
Why the reported percentages differ
The figures are not direct comparisons of identical measurements. The studies differ in geographic coverage, years examined, crops and crop types, ozone data, exposure measures, and methods for translating exposure into yield effects.
- Geography: the 2022 assessment covers China, Japan, and South Korea; the 2025 analysis is China-only. The Yangtze River Delta and southern China studies are narrower still.
- Exposure and response: studies use different ozone measures and sources, including monitored or reanalysis exposure and response relationships derived from experiments or regional analyses.
- Crop and season: wheat, maize, and rice do not have identical exposure or response patterns. Rice estimates may also distinguish hybrid from inbred varieties or double-early from double-late crops.
- Spatial and temporal representation: the accuracy of ozone data across locations and growing seasons, and the way response estimates are extrapolated, affect the result.
Liu et al. explicitly note uncertainty related to ozone metrics and extrapolation. Read each percentage alongside its study, location, period, and method rather than treating the largest reported number as a universal estimate.
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What the evidence says about future risk and responses
Liu et al. project that China’s national relative yield loss could reach 8%–18% by 2050 under their business-as-usual scenario without emission control. This is a scenario conditional on its assumptions, not an inevitable forecast.
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1Clear out junk files and repair common Windows errors2Fix the driver behind crashes, sound loss and screen glitches3Repair Windows errors before they cause bigger problemsThe studies identify ozone precursor-emission control and adaptive agronomic measures as relevant responses. Liu et al.’s 2020 finding does not establish the isolated effect of a specific long-term policy or farm treatment; it reports an exposure decrease associated in the analysis with lockdown conditions. The cited studies do not substantiate a particular consumer device, seed, or chemical as a solution to regional ozone-related losses.
What is—and is not—known for East Asia today
The newer trend and national yield estimates discussed above apply to China, not all of East Asia. The available studies do not establish comparable up-to-date country-specific trends for Japan and South Korea through 2026. A 2004 assessment included all three countries, but its values for 2020 were projections made at that time, not observations of present-day conditions.
For the underlying study records, see Feng et al., “Ozone pollution threatens the production of major staple crops in East Asia”; Liu et al., “Ozone pollution induced-yield loss of major staple crops in China and effects from COVID-19”; the Yangtze River Delta study; the 2004 China, Japan, and South Korea assessment; and the southern China rice study.
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