News | February 6, 2012

Ozone Pollution Damage Crops Across Continents

Man-made air pollution from Southeast Asia causes the loss of 6.7 million tonnes of wheat and about 11.6 million tonnes of rice globally each year, while pollutants from North America reduce wheat yields in Europe by 1.2 million tonnes each year, according to a new study.

The study shows that ozone pollution causes millions of tonnes of crop losses not just in the regions where it's emitted, but also across continents. On a global scale, pollution from Southeast Asia has the biggest impact.

The research, led by the University of Leeds and co-authored by researchers from the Stockholm Environment Institute at the University of York, shows for the first time the extent of the Northern Hemisphere's intercontinental crop losses caused by ozone – a chemical partly produced by burning of fossil fuels.

Dr Lisa Emberson, a senior research associate from Stockholm Environment Institute at the University of York, says: "This study highlights the need for air pollution impacts on crops to be taken more seriously as a threat to food security. Given the sizeable yield losses of staple crops caused by surface ozone, there should be greater coordinated international efforts focused on reducing emissions of ozone-forming gases across the globe."

The study 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.

The paper, Intercontinental trans-boundary contributions to ozone-induced crop yield losses in the Northern Hemisphere, published in Biogeosciences, show how ozone pollution generated in each of the Northern Hemisphere's major industrialised 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 kilometres downwind.

Of the yield losses to Europe caused by ozone, pollution originating from North America is responsible for a 1.2 million tonnes annual loss of wheat. This is 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.

Dr Emberson says: "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."

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).

The scientists used a computer model to predict reductions in global surface ozone if man-made emissions of nitrogen oxide from the three continents were eliminated. Using crop location and yield calculations, the research team was able to predict impacts on staple food crops, each with their own unique sensitivity to ozone pollution.

Dr Steve Arnold, a senior lecturer in atmospheric composition at the University of Leeds's School of Earth and Environment, who led the study, said: "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."

Other findings are:

  • In terms of global crop losses, Asian pollution dominates worldwide losses of wheat (50-60 per cent) and rice (more than 90 per cent).
  • North American pollution contributes the most to worldwide losses of maize (60-70 per cent) and soybean (75-85 per cent).
  • 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.

Dr Arnold added: "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."

The study was jointly funded by the Natural Environment Research Council and the Met Office in the UK.

Facts and link to the paper: Total European wheat production is around 130 million tonnes a year. Europe's own pollution remains the biggest contributor to its wheat crop loss (3.5 million tonnes a year).

Most people will have heard of ozone in the context of the "ozone layer". This is a region of enhanced ozone at 20-30 km altitude. Here, the ozone is formed by a different natural process and plays an important role in filtering out harmful ultra-violet radiation (responsible for skin cancers). In summary, ozone in the ozone layer is good ozone; ozone at the surface is bad ozone.

Other researchers have recently published results quantifying the global losses in crop productivity from global ozone pollution and the economic implications, without the continental breakdown this study shows.

The paper Intercontinental trans-boundary contributions to ozone-induced crop yield losses in the Northern Hemisphere by Michael Hollaway, Dr Steve Arnold, Prof Andy Challinor and Dr Lisa Emberson was published on 16 January 2012 and is available at:

SOURCE: Stockholm Environment Institute