Tropospheric ozone


Tropospheric ozone emissions sources and impacts
Tropospheric ozone emissions sources and impacts
WHAT IS Tropospheric Ozone?

Smog over a city

Ozone (O3) is a reactive gas that exists in two layers of the atmosphere: the stratosphere (upper layer) and the troposphere (at ground level and up to 15km). In the stratosphere, ozone protects life on Earth from the sun’s ultraviolet radiation. In contrast, at lower levels, it is an important greenhouse gas and air pollutant, which is harmful to human and ecosystem health. It is also a major component of urban smog.

Tropospheric ozone is a short-lived climate pollutant with an atmospheric lifetime of hours to weeks. It does not have any direct emissions sources, rather it is a secondary gas formed by the interaction of sunlight with hydrocarbons – including methane – and nitrogen oxides, which are emitted by vehicles, fossil fuel power plants, and other man-made sources.

Strategies to prevent the formation of tropospheric ozone are primarily based on methane reductions and cutting the levels of atmospheric pollution arising from man-made sources, such as agriculture and fossil fuel production and distribution.

Key figures
Hours-weeks 79–121 million 1 million
Tropospheric ozone has an atmospheric lifetime ranging from a few hours to a few weeks in polluted urban regions Estimated global crop production losses owing to ozone total 79–121 million tonnes, worth USD 11–18 billion annually Long-term exposure to ozone air pollution is linked to 1 million premature deaths per year due to respiratory diseases
PRIMARY SOURCES OF Tropospheric Ozone

In the troposphere, ozone is the product of the atmospheric reaction of a number of precursor pollutants, which have both natural and man-made sources. Precursor pollutants created by human activities include hydrocarbons and nitrogen oxides, which are largely emitted by cars and other vehicles, fossil fuel power plants, oil refineries, the agriculture sector and a number of other industries.

Population-weighted ozone concentrations

Tropospheric Ozone IMPACTS

Ozone absorbs radiation and consequently acts as a strong greenhouse gas. Tropospheric ozone affects the climate beyond increased warming, having impacts on evaporation rates, cloud formation, precipitation levels, and atmospheric circulation. These impacts mainly occur within the regions where tropospheric ozone precursors are emitted, and so disproportionally affect the Northern Hemisphere.

Population-weighted ozone concentrations


Tropospheric ozone is a major component of smog, which can worsen bronchitis and emphysema, trigger asthma, and permanently damage lung tissue. Tropospheric ozone exposure is responsible for an estimated one million premature deaths each year. Children, the elderly, and people with lung or cardiovascular diseases are particularly at risk of the adverse health impacts of ozone.


Tropospheric ozone is a highly reactive oxidant that significantly reduces crop productivity as well as the uptake of atmospheric carbon by vegetation. Its effects on plants include impeded growth and seed production, reduced functional leaf area and accelerated ageing.

Studies have shown that many species of plants are sensitive to ozone, including agricultural crops, grassland species and tree species. These effects impact on the important ecosystem services provided by plants, including food security, carbon sequestration, timber production, and protection against soil erosion, avalanches and flooding.


Strategies to prevent the formation of tropospheric ozone are primarily based on methane reductions.

The relatively short atmospheric lifetime of methane, combined with its strong warming potential, means that targeted strategies to reduce emissions can provide climate and health benefits within a few decades.

The Coalition supports implementation of control measures that, if globally implemented by 2030, could reduce global methane emissions by as much as 40%. Several of these emission reductions could be achieved with net savings, providing quick benefits for the climate as well as public health and agricultural yields.

METHANE - 40% emissions reduction potential globally by 2030


  • Improve manure management and animal feed quality

  • Apply intermittent aeration of continuously flooded rice paddies

  • Improve animal health and husbandry by combining herd and health management, nutrition and feeding management strategies

  • Introduce selective breeding to reduce emission intensity and increase production

  • Promote farm-scale anaerobic digestion to control methane emissions from livestock

  • Adopt guidelines on healthy dietary choices

  • Carry out pre-mining degasification and recovery and oxidation of methane from ventilation air from coal mines

  • Reduce leakage from long-distance gas transmission and distribution pipelines

  • Extend recovery and utilization from gas and oil production

  • Recover and use gas and fugitive emissions during oil and natural gas production


  • Separate and treat biodegradable municipal waste, and turn it into compost or bioenergy

  • Upgrade wastewater treatment with gas recovery and overflow control

  • Improve anaerobic digestion of solid and liquid waste by food industry

  • Upgrade primary waste water treatment

  • Divert organic waste

  • Collect, capture and use landfill gas

More control measures 

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