American ozone depletes European wheat

Air pollution from North America causes Europe to lose 1.2 million tons of wheat a year, a new study shows. Published in the journal Biogeosciences, the research shows for the first time the extent of the Northern Hemisphere’s intercontinental crop losses caused by ozone—and also suggests that increasing levels of air pollution from one continent may partly offset efforts to cut carbon emissions in another. The findings have important implications for international strategies to tackle global food shortages, as well as global climate and human health strategies. Researchers show how pollution from ozone—a chemical partly produced by fossil fuels—that is generated in each of the Northern Hemisphere’s major industrialized regions (Europe, North America, and South East Asia) damages six important agricultural crops (wheat, maize, soybean, cotton, potato, and rice) not only locally, but also by travelling many thousands of kilometers downwind. Of the yield losses to Europe caused by ozone, pollution originating from North America is responsible for a 1.2 million ton annual loss of wheat—the biggest intercontinental ozone-related impact on any food crop. The scale of the impact of North American pollution on European wheat has previously been unknown. “Our findings demonstrate that air pollution plays a significant role in reducing global crop productivity, and show that the negative impacts of air pollution on crops may have to be addressed at an international level rather than through local air quality policies alone,” says Steve Arnold, a senior lecturer in atmospheric composition at the University of Leeds, who led the study. Researchers calculated projected levels of surface ozone concentration, a powerful air pollutant that is not only harmful to human health (particularly to the respiratory system) but also damages vegetation by damaging plant cells and inhibiting plant growth. Enhanced surface ozone concentrations are produced through a chemical combination of hydrocarbon compounds and nitrogen oxides (nitrogen oxides are emitted into the atmosphere during high temperature combustion, for example by combustion of fossil fuels by motor vehicles and in coal fired power plants). Michael Hollaway, a PhD student at the University of Leeds, used a computer model to predict reductions in global surface ozone if man-made emissions of nitrogen oxide from the three continents were shut off. Using crop location and yield calculations, researchers were able to predict impacts on staple food crops, each with their own unique sensitivity to ozone pollution. “This study highlights the need for air pollution impacts on crops to be taken more seriously as a threat to food security,” says Lisa Emberson a senior lecturer from the University of York’s Stockholm Environment Institute and Environment Department. “Currently air quality is often overlooked as a determinant of future crop supply Given the sizeable yield losses of staple crops caused by surface ozone, coupled with the challenges facing our ability to be food secure in the coming decades further coordinated international  efforts should be targeted at reducing emissions of ozone forming gases across the globe.” Other findings are: In terms of global crop losses, Asian pollution dominates worldwide losses of wheat (50-60 percent) and rice (more than 90 percent). North American pollution contributes the most to worldwide losses of maize (60-70%) and soybean (75-85 percent). The impact of Europe’s pollution on other continents is minor due to fewer low pressure systems and weather fronts, which are responsible for transporting pollution across continents. “With future emissions of ozone-forming chemicals from Europe and North America expected to reduce, and emissions from Asia to increase, the findings suggest that increasing pollution from Asia may partly offset crop production benefits gained in Europe and North America through local emission reduction strategies,” says Arnold. The study was jointly funded by the Natural Environment Research Council and the Met Office.