New Research Finds Reducing Common Air Pollutants can Increase Crop Yields

A new study finds that common air pollutants are harming agricultural productivity. The research finds that reducing nitrogen oxides could increase crop yields around the globe, and as much as 28% in some regions. Authored by NASA Harvest partners at Stanford University’s Center on Food Security and the Environment, the findings illustrate the complex relationship between air quality and vegetation health and provide additional benefits to reducing a common air pollutant.

Researchers have long thought that air pollution could negatively affect crop condition, but estimates varied widely on the actual impact. This was a result of the difficulty in creating experiments able to effectively measure and compare both factors due to the limited geographic overlap between air quality monitoring stations and agricultural land. The authors note that previous studies have attempted to account for this by comparing power plant-adjacent cropland yields before and after plant construction. This form of analysis is limited in its effectiveness however as it is limited to areas with known pollution sources and doesn’t allow researchers to distinguish between different pollutants.

This recent research from Stanford overcomes these limitations through the use of Earth observation data obtained from satellite imagery. Advances in remote sensing have allowed for near-global coverage and the ability to detect a variety of air pollutants. Combined with well established methods for monitoring crop health throughout a growing season, the team at Stanford was able to correlate nitrogen dioxide (NO2) levels (a proxy for overall nitrogen oxide levels) and the health of cropland in five major food-producing regions around the world.

Lead study author, David Lobell, elaborates “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”.

The study looked at winter and summer crops in the United States, India, China, Western Europe, and South America. Each region had a wide variation in NO2 emissions though China led the group in overall NO2 emissions, followed by India and Western Europe. The United States and South America generally had the lowest overall levels of emissions.

(A) Image from the article showing global amounts of NO2 emissions. Five regional maps show NO2  levels in pixels where wheat is more than 2% of land area. (B) Histograms showing NO2 levels for each region and year.

The authors found that NO2 levels are generally lower in summer than in winter, thereby reducing the potential yield gains from NO2 emission reduction. Despite this, each region would still benefit from reducing summer NO2 emissions with China in particular potentially seeing a 15% increase in yield gains. India, Western Europe, The United States, and South America also see big benefits with 5.1%, 10.6%, 8.7%, and 2.1% increases respectively.

Given the generally higher NO2 levels in winter than in summer months, many regions see an even greater potential increase in yield gains for winter crops. China, with its significantly higher NO2 levels, could see a 28% increase in crop yields — a near doubling of the benefits for its summer crops and three to four times as much for the other four regions. India, Western Europe, and South America could see 6.4%, 8.7%, and 7.4% increases respectively. The United States already has very low winter NO2 levels and would see minimal yield gains from decreased NO2 emissions.

Map from study showing estimated potential yield gains from NO2 emission reductions. Percent changes assume reducing 2020 NO2 levels to the 5th percentile observed in the given region.

This research shows the significant benefits of reducing NO2 emissions. Reduction schemes could play a major role in increasing overall food production, supporting the globe’s growing population, and combating global food insecurity. Encouraged by these results, the authors anticipate future work exploring the impact of other air pollutants as well as investigating how different combinations of pollutants and meteorological variables explain the variability in crop health across years within regions.

The open access article, Globally Ubiquitous Negative Effects of Nitrogen Dioxide on Crop Growth, was authored by Harvest partners at Stanford University's Center on Food Security and the Environment, David B. Lobell, Stefania Di Tommaso, and Jennifer A. Burney.