Climate science at a glance
- Surface-level ozone and particulate matter are common air pollutants that pose a serious risk to human health and the environment.
- Changes in temperature and precipitation can increase air quality risks from surface-level ozone.
- Climate warming generally increases surface-level ozone across the United States.
Surface versus stratospheric ozone
Unlike stratospheric ozone, which forms naturally in the upper atmosphere and protects people from the sun's harmful ultraviolet rays, surface-level (or tropospheric) ozone is created through the interactions of gases caused by human and natural emissions.
Ozone formation and precursors
The majority of tropospheric ozone formation occurs when nitrogen oxides (NOx), carbon monoxide (CO) and volatile organic compounds (VOCs) react in the atmosphere in the presence of sunlight.
NOx, CO, and VOCs are called ozone precursors. Ozone concentrations depend on emissions of these precursors as well as weather conditions such as temperature, humidity, cloud cover, and winds. These emissions come from a variety of human sources, such as power plants and motor vehicles, and from natural sources, such as forests and wildfires.
Climate change impacts on ozone
Changes in air temperature and water content affect the air's chemistry and the rates of chemical reactions that create and remove ozone. Many chemical reaction rates increase with temperature and lead to increased ozone production.
In particular, increasing temperatures increase the decomposition of the pollutant known as peroxyacetylnitrate (PAN), which is a major reservoir species for long range transport of the ozone precursors NOx and HOx. This means increasing temperature decreases the lifetime of PAN, altering the long-range transport of ozone pollution.
Human health impacts of surface ozone
Adverse human health impacts associated with exposure to surface-level ozone include premature death, respiratory hospital admissions, cases of aggravated asthma, lost days of school, and reduced productivity among outdoor workers.
US surface ozone trends and climate change
- Model simulations looking at air quality over 1980–2014 indicate that climate warming generally increases surface-level ozone across the United States, but results differ spatially and in the magnitude of the projected signal.
- Warmer August temperatures in the Southeast from 1988 to 2011 were associated with increased human sensitivity to surface-level ozone.