Photo: Flickr/2010CIAT/NeilPalmer (CC BY-SA 2.0)
Air pollution takes a toll on people’s health, but air quality has several other effects as well. One is that polluted air can lower crop yields. The corollary is that cleaner air can boost those yields.
Researchers in the United States have discovered that reductions in air pollution during a two-decade period between 1999 and 2019 helped bring about a 20% increase in corn and soybean yields worth about $5 billion a year.
The scientists, who focused on a region of nine states region in the U.S. that produces two-thirds of the country’s maize and soybean, found that four air pollutants are particularly damaging to crops: ozone, particulate matter, sulfur dioxide, and nitrogen dioxide.
These pollutants accounted for an estimated 5% loss in corn and soybean production in the region during the study period, based on data and yield estimates.
Specifically, total yield losses averaged 5.8% for maize and 3.8% for soybean over the two decades. Yet as the air grew cleaner over time, these losses declined and eventually gave way to a 4% growth in corn yields and 3% growth in soybean yields. The increases equaled 19% of corn’s overall yield gains and 23% of soybeans’ overall yield gains during the period.
“Air pollution impacts have been hard to measure in the past, because two farmers even just 10 miles apart can be facing very different air quality,” explains David Lobell, director of Standford University’s Center on Food Security and the Environment. “By using satellites, we were able to measure very fine scale patterns and unpack the role of different pollutants.”
Although it has long been known chronic air pollution, including ozone, sooth and smoke, is toxic to plants, it has come as a surprise how much crop yields can suffer as a result.
For their new study, the American researchers examined air pollution data from hundreds of monitoring stations around the region, in addition to federal data on power plant emissions, satellite-based observations of nitrogen dioxide around those power plants, crop yield data from federal surveys and satellite imagery, as well as weather data to account for growing season conditions known to explain crop yield variations.
“This has been a tricky problem to untangle because historically our measurements of different types of air pollutants and our measurements of agricultural yields haven’t really overlapped spatially at the necessary resolution,” says Jennifer Burney, an associate professor of environmental science at the University of California, San Diego.
“With the new high spatial resolution data, we could look at crop yields near both pollution monitors and known pollutant emissions sources. That revealed evidence of different magnitudes of negative impacts caused by different pollutants,” she adds.
The scientists found that the further away plants were from power plants, particularly coal-burning ones, the better their yields.
“We already know that the Clean Air Act resulted in trillions of dollars of benefits in terms of human health, so I think of these billions in agricultural benefits as icing on the cake,” Lobell explains.
“But even if it’s a small part of the benefits of clear air, it has been a pretty big part of our ability to continue pushing agricultural productivity higher,” he adds.
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