Methane (CH₄) is primarily known as strong greenhouse gas, which contributes to global warming. Less widely known is its role in the formation of ground-level ozone (O₃). Ground-level ozone is formed by the chemical reaction of methane (CH₄), carbon monoxide (CO) and volatile organic compounds (VOCs) with nitrogen oxides (NOx) under the influence of UV radiation from sunlight. This reactive gas is not only harmful to human health, but also causes extensive damage to plants and ecosystems.

The damage that ozone causes to agricultural crops is not small. According to the World Meteorological Organization (WMO), global crop losses due to ozone damage between 2010 and 2012 were estimated at approximately 12.4 % for soybeans, 7.1 % for wheat, 4.4 % for rice and 6.1 % for maize. These losses totalled 227 million tonnes of the four staple crops, which is significant impact on local economies and global food security.

The problem is global, with key factors being climatic conditions, regional pollution levels and the type of agricultural production. Particularly vulnerable regions include eastern China, Korea, Japan and parts of India, as well as several states along the west coast of the US, the central and northeastern regions and southern Canada. In Europe, ozone levels are highest in the Mediterranean region, but ozone damage affects most of the continent's agricultural areas.

According to a 2022 EU study, nine member states lost more than five percent of their wheat harvest and eleven experienced similar losses in potatoes. Poland was the worst hit, losing 10 % of its potato harvest, while Belgium experienced wheat losses exceeding 7 %. In absolute terms, the largest losses were recorded in large producing countries such as France, Germany, Poland and the Netherlands.. For example, in France, absolute wheat losses in 2022 were 2.5 million tons, followed by Germany (1.4 million tons) and Poland (465 thousand tons). The ozone level in 2022 was not exceptional, but rather typical.

Plants absorb ozone through their stomata, the same pores they use to take in carbon dioxide during photosynthesis. Once ozone reaches plant cells and the plant's natural antioxidants are depleted, damage occurs. This leads to impaired photosynthesis, reduced growth and often smaller seeds with lower nutritional content. Legumes also have a reduced ability to fix nitrogen, which may explain why soybeans are the most ozone-sensitive of the major crops.

Farmers often don't realize that lower crop yields are linked to this colorless gas. Brown spots on leaves are commonly mistaken for drought or pest damage. Although the most extreme ozone peaks have been mitigated by reduced NOx and VOC emissions, they have increased globally. levels of so-called "baseline" ozone, mainly due to increasing concentrations of methane. Methane, with an average atmospheric lifetime of about 12 years, persists much longer than other ozone precursors (which have lifetimes of only days or weeks), thus global impact on ozone levels.

Tackling methane emissions is therefore crucial. If ozone damage to crops is included in the calculation of environmental costs, the marginal cost of methane emissions could be increase by another 15-30 %, which is 423-556 USD per ton. For this reason, stronger methane policies represent a benefits for agriculture, food security, public health and climate. It is recommended, for example, to set binding EU targets for methane reduction, to integrate methane into air quality legislation and to replace the ozone risk assessment method AOT40 with the more scientifically accurate PODY (Phytotoxic Ozone Dose) flux metric.. JRi

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