Why ground-level ozone air pollution is a risk to food security
According to an IPCC scenario, the concentration of ground-level or tropospheric ozone (O3) may reach 70 ppb in 2050. Then, more than 30% of global cereal acreage could be exposed to significant ozone pollution, which in turn would lead to significantly lower crop yields.
Ground-level or tropospheric ozone (O3) is ingested by plants through their stomata (pores in the epidermis of plants) and has a growth-inhibiting effect: O3 leads to a reduced rate of photosynthesis, increased respiration and accelerated ageing of leaves. O3 also increases the plants’ susceptibility to diseases and other stress factors. O3 is also thought to alter the concentration of nitrogen, carbohydrates and phenols in the leaf and grain.
Ozone ingestion by plants is strongly dependent on the functioning of the stomata: In very dry areas, the stomata opens very little to prevent water loss, thus offering little opportunity for ozone to be ingested by the plant. However, as soon as artificial irrigation takes place, this mechanism is overridden.
Large-scale studies in the USA (NCLAN, National Crop Loss Assessment Network) and Europe (EOTCP, European Open-Top Chamber Program) have demonstrated significant yield losses in crops: Already at current ozone levels, yield losses in European field trials for cereals were 5-15%; at exposures above 60 ppb, losses increase to up to 60%.
Calculations within an IPCC scenario expect O3 concentrations to continue to rise, possibly reaching 70 ppb by 2050. Then, more than 30% of the global cultivated area of cereals could be exposed to significant ozone pollution. This means not only serious financial losses in agriculture but also a serious food supply problem.
Where can we start?
Tropospheric or ground-level ozone (O3) is not emitted directly into the air but is formed by chemical reactions between nitrogen oxides (NOx) and volatile organic compounds (VOCs). This happens when pollutants emitted from cars, power plants, industrial boilers, refineries, chemical plants and other sources react chemically in the presence of sunlight.
Ozone can be transported over long distances by the wind, so high ozone levels can occur even in rural areas.
From this, if the sources of precursors are identified, effective action can be taken. Correlations of O3 pollution with weather and wind data are as fundamental as NOx correlations with traffic.
