Analysis of air pollution and crop health via satellite imagery suggests that limiting emissions of nitrogen dioxide, a potent greenhouse gas, could boost crop yields by up to 28 per cent
1 June 2022
Slashing nitrogen dioxide emissions to 5 per cent of current levels could increase crop yields in China by up to 28 per cent. Limiting this type of air pollution would also improve crop yields in other regions of the world.
“China continues to see some of the highest nitrogen oxide levels in the seasons and places where crops are growing,” says David Lobell at Stanford University in California.
There are two main ways nitrogen oxides affect crop yields, he says. “Nitrogen oxide is a phytotoxin, meaning it directly damages plant cells. But it is also a key factor in the formation of other pollutants such as ozone, which are themselves damaging to plants.”
To quantify the effects of this potent greenhouse gas on crops, Lobell and his colleagues analysed satellite images of crops in the US, China, India, western Europe and South America between 2018 and 2020.
They rated how green the images were, as previous studies had found that crop greenness measured using satellites is strongly linked to crop growth and yield. They then compared this rating with each region’s nitrogen dioxide levels, taken from satellite data that can track the gas’s unique spectral signature. Lobell says nitrogen dioxide is a good measure of the levels of nitrogen oxides, a group of highly reactive gases.
Using the data, the team modelled what would happen to crop yields in each region if nitrogen dioxide pollution were reduced to 5 per cent of current emissions. The team estimated that in China, such a cut would lead to a 28 per cent increase in crop yield during the winter and a 17 per cent rise in the summer.
The seasonal difference stems from the fact that nitrogen oxide levels are often higher in the winter, says Lobell. Out of all the regions analysed, China would experience the biggest impact in cutting nitrogen oxide pollution.
The researchers also found that western Europe would see close to a 10 per cent rise in both winter and summer crop yields. Meanwhile, India could expect a 6 per cent increase for winter and an 8 per cent increase for summer crops.
North and South America had the smallest link between nitrogen oxide levels and crop yield, the team found. “One reason is that, although urban areas in the Americas can see very high levels of the pollutants, the cities tend to be more removed from the agricultural regions,” says Lobell.
The main way to cut nitrogen oxide pollution to background levels is to change global energy and transport systems, says Lobell. “We have seen historical cases of rapid declines, such as Los Angeles in the late 20th century and China more recently,” he says. “Progress is possible.”
“This study provides another argument for action… on sustainable nitrogen management,” says Mark Sutton at the UK Centre for Ecology and Hydrology.
The study also highlights the significance of the proposed European Space Agency mission to launch Nitrosat, a satellite that can combine measurements of nitrogen dioxide and ammonia at high resolution, he says. “This would give us massively increased power to better understand and quantify such effects as explored by this study,” he says.
Journal reference: Science Advances, DOI: doi.org/10.1126/sciadv.abm9909
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