Ground-level ozone is very different from the protective ozone layer high in the atmosphere. Near the ground, ozone is a harmful air pollutant that forms when nitrogen oxides and volatile organic compounds react in sunlight. The U.S. Environmental Protection Agency explains that these precursor pollutants come from sources such as vehicles, power plants, industrial facilities, gasoline vapors, and chemical solvents.
Climate change matters because temperature, sunlight, atmospheric circulation, and drought all influence the chemistry that creates and moves ozone. EPA research warns that atmospheric warming has the potential to increase ground-level ozone in many regions, creating an additional challenge for communities already trying to meet air-quality standards. This interaction is sometimes called a climate penalty because warmer conditions can make ozone pollution harder to control even when precursor emissions are declining.
Heat and Sunlight Can Increase Ozone Formation
Ozone is not emitted directly from a tailpipe or smokestack. It forms through chemical reactions involving nitrogen oxides, volatile organic compounds, sunlight, and heat. EPA guidance notes that hot, sunny days are especially favorable for ozone production, which is why ozone problems often become more severe during summer.
Heat waves can intensify those conditions. Long periods of high temperature, strong sunlight, and stagnant air allow ozone-forming pollutants to remain concentrated near the surface. EPA modeling has found that warming temperatures and heat waves associated with higher greenhouse gas emissions could increase ozone concentrations and worsen public-health impacts.
Recent NOAA research also shows that the relationship is more complicated than temperature alone. A 2025 analysis of U.S. surface ozone trends examined the impact of heat waves on ozone across the United States from 1990 through 2023. The study highlights how heat, emissions, atmospheric chemistry, and regional conditions interact, which is why air-quality managers need both emissions data and weather information when forecasting ozone episodes.
Ozone Can Travel Far Beyond Its Sources
Ground-level ozone is a regional pollutant as well as a local one. The precursor chemicals that create ozone can travel downwind before reacting, and ozone itself can move between cities, agricultural areas, and states. EPA notes that rural regions can experience high ozone concentrations because winds carry pollution hundreds of miles from its original sources.
Weather patterns therefore influence where ozone accumulates. Changes in wind direction, atmospheric stability, temperature, and mixing can shift pollution from one area to another. A city may reduce some local emissions yet still experience high ozone when polluted air arrives from upwind regions.
This is one reason regional cooperation is important. Ozone management often requires coordinated reductions in nitrogen oxides and volatile organic compounds across transportation, power generation, industry, and other sectors. Monitoring systems that combine emissions data, weather forecasts, and ozone measurements can help identify when pollution is likely to move or intensify.
Ground-Level Ozone Can Damage Plants and Crops
Ozone affects more than human breathing. It enters leaves through stomata, the small openings plants use for gas exchange, and can interfere with photosynthesis and plant growth. EPA describes ground-level ozone as a pollutant that can damage crops and ecosystems as well as cause respiratory health problems.
The effects on agriculture can be substantial. A peer-reviewed review indexed by EPA estimated global yield losses associated with ozone exposure at approximately 2.2% to 5.5% for maize, 3.9% to 15% for wheat, and 8.5% to 14% for soybean. The exact effect varies by crop variety, ozone concentration, environmental conditions, and plant sensitivity, but the numbers show why ozone is an agricultural as well as an urban air-quality issue.
Evidence also exists from South Asia. Research on crops near Peshawar in northwestern Pakistan found visible ozone injury on potato, onion, and cotton when monthly ozone concentrations exceeded 45 parts per billion. In fumigation experiments, daytime ozone concentrations of 60 parts per billion significantly reduced the growth of a major Pakistani onion variety, showing that ozone exposure can affect crop performance under conditions already found in the region.
Cutting Precursor Emissions Can Reduce Multiple Risks
The main way to reduce ground-level ozone is to cut emissions of the chemicals that form it. Nitrogen oxides and volatile organic compounds come from motor vehicles, power plants, industrial processes, fuel combustion, solvents, and other sources. Reducing those emissions decreases the raw materials available for ozone formation.
Many of the same changes can also reduce greenhouse gas emissions. Cleaner electricity, more efficient transportation, low-emission vehicles, energy efficiency, and reduced fossil-fuel combustion can lower both climate pollution and ozone-forming emissions. EPA research shows that full implementation of existing air-pollution regulations can offset some of the ozone increases caused by warmer temperatures.
The relationship between ozone and climate is not identical everywhere. Local emissions, vegetation, drought, sunlight, wind, and atmospheric chemistry all affect ozone concentrations differently. NOAA research from the North China Plain, for example, found that hot and dry conditions, vegetation changes, aerosol reductions, and biogenic volatile organic compounds all contributed to high-ozone events, illustrating why ozone control needs to account for both emissions and changing climate conditions.
Ground-level ozone is a good example of how climate change and air pollution can reinforce one another. Hotter temperatures and heat waves can create more favorable conditions for ozone formation, while ozone itself damages human health, crops, and natural vegetation. Reducing ozone-forming pollutants while also cutting greenhouse gas emissions can therefore deliver benefits for air quality, agriculture, ecosystems, and climate resilience at the same time.
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