Reducing nitrogen dioxide emissions to 5% of current levels could boost crop yields in China by up to 28%. Limiting this type of air pollution would boost crop yields in other parts of the world as well. "China continues to have some of the highest nitrogen oxide levels during crop seasons and in crop-growing areas," says David Lobell of Stanford University in California.
According to him, nitrogen oxides have two major effects on crop yields. "Nitrogen oxide is a phytotoxin, which means that it directly harms plant cells." However, it is also a major contributor to the formation of other pollutants, such as ozone, which are harmful to plants."
Lobell and his colleagues examined satellite images of crops in the United States, China, India, Western Europe, and South America between 2018 and 2020 to quantify the effects of this potent greenhouse gas on crops.
They rated how green the images were because previous research had found that crop greenness measured with satellites is strongly related to crop growth and yield. They then compared this rating to nitrogen dioxide levels in each region, as measured by satellite data that can track the gas's unique spectral signature. According to Lobell, nitrogen dioxide is a good indicator of the levels of nitrogen oxides, a class of highly reactive gases.
Using this information, the team calculated what would happen to crop yields in each region if nitrogen dioxide pollution were reduced to 5% of current levels. According to the team, such a cut would result in a 28% increase in crop yield during the winter and a 17% increase in crop yield during the summer in China.
According to Lobell, the seasonal difference is due to higher nitrogen oxide levels in the winter. China would have the greatest impact on reducing nitrogen oxide pollution of any of the regions studied.
The researchers also discovered that both winter and summer crop yields in Western Europe would increase by close to 10%. Meanwhile, India may see a 6% increase in winter crops and an 8% increase in summer crops.
The team discovered the smallest link between nitrogen oxide levels and crop yield in North and South America. "One reason is that, while urban areas in the Americas can see very high levels of pollution, cities tend to be more removed from agricultural regions," Lobell explains.
According to Lobell, the main way to reduce nitrogen oxide pollution to background levels is to change global energy and transportation systems. "We've seen examples of rapid declines in the past, such as Los Angeles in the late twentieth century and China more recently," he says. "Progress is attainable."
"This study adds to the case for action... on sustainable nitrogen management," says Mark Sutton of the UK Centre for Ecology and Hydrology.
According to him, the study also emphasizes the significance of the proposed European Space Agency mission to launch Nitrosat, a satellite that can combine high-resolution measurements of nitrogen dioxide and ammonia. "This would give us vastly increased power to better understand and quantify such effects as those investigated in this study," he added.
