Cutting air pollution will improve yields of common crops, study finds
Image credit: Dreamstime
Nitrogen oxides, the common air pollutants typically produced by vehicle exhausts, have been shown to lower crop yields, according to a Stanford University-led study.
The analysis used satellite images to reveal for the first time how nitrogen oxides affect crop productivity. The researchers believe the findings have important implications for increasing agricultural output and analysing climate change mitigation costs and benefits around the world.
“Nitrogen oxides are invisible to humans, but new satellites have been able to map them with incredibly high precision. Since we can also measure crop production from space, this opened up the chance to rapidly improve our knowledge of how these gases affect agriculture in different regions,” said study lead author David Lobell.
Nitrogen oxides, or NOx, are among the most widely emitted pollutants in the world. These gases can directly damage crop cells and indirectly affect them through their role as precursors to formation of ozone, an airborne toxin known to reduce crop yields, and particulate matter aerosols that can absorb and scatter sunlight away from crops.
The team combined satellite measures of crop greenness and nitrogen dioxide levels for 2018-2020. Nitrogen dioxide is the primary form of NOx and a good measure of total NOx. Although NOx is invisible to humans, nitrogen dioxide has a distinct interaction with ultraviolet light that has enabled satellite measurements of the gas at a much higher spatial and temporal resolution than for any other air pollutant.
“In addition to being more easily measured than other pollutants, nitrogen dioxide has the nice feature of being a primary pollutant, meaning it is directly emitted rather than formed in the atmosphere,” said study co-author Jennifer Burney. “That means relating emissions to impacts is much more straightforward than for other pollutants.”
Based on their observations, the researchers estimated that reducing NOx emissions by about half in each region would improve yields by about 25 per cent for winter crops and 15 per cent for summer crops in China, nearly 10 per cent for both winter and summer crops in Western Europe, and roughly 8 per cent for summer crops and 6 per cent for winter crops in India.
North and South America generally had the lowest NOx exposures. Overall, the effects seemed most negative in seasons and locations where NOx likely drives ozone formation.
“The actions you would take to reduce NOx, such as vehicle electrification, overlap closely with the types of energy transformations needed to slow climate change and improve local air quality for human health,” said Burney. “The main take-home from this study is that the agricultural benefits of these actions could be really substantial, enough to help ease the challenge of feeding a growing population.”
Previous research by Lobell and Burney estimated reductions in ozone, particulate matter, nitrogen dioxide, and sulfur dioxide between 1999 and 2019 contributed to about 20 per cent of the increase in US corn and soybean yield gains during that period – an amount worth around $5bn per year.
Future analysis could incorporate other satellite observations, including photosynthetic activity measured through solar-induced fluorescence, to better understand nitrogen dioxide’s effects on crops’ varying degrees of sensitivity to the gas throughout the growing season, according to the researchers.
Similarly, more detailed examination of other pollutants, such as sulphur dioxide and ammonia, as well as meteorological variables, such as drought and heat, could help to explain why nitrogen dioxide affects crops differently across different regions, years and seasons.
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