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Understanding Air Quality

Everyone wants and deserves clean air to breathe, and the U.S. Clean Air Act has established national air quality goals for the protection of human health and welfare. Tens of billions of dollars are invested each year to reduce air pollution. The results have been impressive. In the more than three decades since the passage of the Clean Air Act, emissions of air pollutants have declined while the Nation's Gross Domestic Product has more than doubled. Despite these efforts and significant progress, the United States still faces challenges in air quality:

  • Almost a third of the population lives in areas where air pollution levels exceed the U.S. Environmental Protection Agency's health-based standards for air quality.
  • Tens of thousands of people die each year as a direct result of exposure to high levels of air pollution; many more suffer adverse health impacts.
  • Crop yields and forest productivity are adversely impacted by exposure to air pollution.
  • Vistas in some of the most pristine areas of the country are often obscured by manmade haze.

The problems are complex and knowledge of the underlying atmospheric processes and sources that control pollution formation and distribution is needed to guide the development of policy and management strategies.

The Science of Air Quality

The quality of the air is the result of a complex interaction of many factors that involve the chemistry and motions of the atmosphere, as well as the emissions of a variety of pollutants from sources that are both natural and anthropogenic. The major pollutant usually associated with poor air quality is ozone. Ozone is naturally present in the atmosphere, but in elevated amounts it is damaging to the living tissue of plants and animals. Ozone is a "secondary" pollutant, meaning that it is formed by the chemical conversion in the atmosphere of other atmospheric species ("precursors"). The ozone precursors are the nitrogen oxides ("NOx", from the burning of fossil fuel, lightning, and other sources) and volatile organic compounds ("VOCs," from fuel burning, natural emissions of vegetation, and other sources). In the presence of sunlight, a series of chemical reactions in the atmosphere creates ozone. Meteorology plays an important role in the conditions that are ripe for making high amounts of ozone; hot, stagnant days cause more ozone to be produced from the NOx and VOC precursors.

Another important aspect of air quality is the presence of fine particles, or "particulate matter" (PM). Fine particles can be either directly emitted ("primary") pollutants or they can be formed within the atmosphere. For example, particles that are directly emitted into the atmosphere include soot particles from burning vegetation (which can be both a natural and a human-caused source), sea-salt spray, blowing dust, and volcanic ash. Other particles can be generated within the atmosphere, such as those arising from chemical conversion of the nitrogen oxides, volatile organic compounds, or sulfur-containing gases emitted from fuel burning, volcanic eruptions, or other sources.

Other components important in air quality include carbon monoxide, sulfur dioxide, NOx and VOCs (ozone precursors, mentioned above), and air toxics such as benzene, mercury and other hazardous air pollutants.

Air Quality Research

NOAA's research scientists are engaged in several approaches to better understand the atmospheric factors that are responsible for poor air quality. Research areas include laboratory studies, intensive field studies, theoretical and modeling studies, and long-term measurements. The research provides environmental policy makers and resource managers better information on (1) the most important processes and sources contributing to poor air quality, (2) the impacts of poor air quality, and (3) potential solutions, including the development of tools to support effective decision-making. The primary customers for this part of NOAA's Air Quality Program are environmental policy-makers and Federal, state, and local air quality managers.

Laboratory Studies

Laboratory investigations are employed to characterize and quantify fundamental properties of chemical reactions, which are needed by predictive models and point the way to specific field study approaches. NOAA's experimental laboratory chemical kinetics program characterizes the fundamental photochemical atmospheric processes (such as the rate of chemical reactions and their reaction products).

Intensive Field Studies

Intensive field studies provide the observations to test the predictive capabilities of models, as well as indicate the potential for hitherto unknown processes that should be examined in the laboratory.

NOAA Current and planned field studies - click on studies for more information

US map showing locations of air quality studies East Tennessee Ozone Study Texas Air Quality Study New England Air Quality Study Bay Region Atmospheric Chemistry Study Central California Ozone Study

NOAA aircraft serve as flying laboratories that support regional air quality assessments. The NOAA Lockheed WP-3D Orion aircraft are ideally suited to studies that cover large distances requiring extensive measurement packages, while aircraft such as the DeHavilland Twin Otter are better suited to more localized experiments with more modest measurement needs. Many of the areas with the most severe air quality problems are in coastal areas. The NOAA Research Vessel Ronald H. Brown has been equipped for air quality studies providing new perspectives on air pollution transport and transformation in coastal waters.

Air Quality Modeling

Theoretical models embody the current understanding of the underlying science and via sensitivity studies, can evaluate the impact of specific processes and emissions on air quality on a local, regional and continental scale. These analyses can be used to identify those areas where improved understanding will result in the biggest payoff, providing direction for laboratory investigations and aiding in the design of intensive field studies. NOAA scientists have played a leading role in the development of the grid-based air quality modeling suite used for regulatory applications. NOAA is also contributing to the development of an air quality model based on the Weather Research Forecast (WRF) framework - WRF-CHEM. In addition NOAA has developed trajectory models such as HYSPLIT for air quality applications.

Air Quality Monitoring of Long-term Trends

Research networks provide information on trends in regional air quality and deposition that provide a mechanism to track trans boundary pollution flow, quantify the impacts of emission reduction programs, and provide context for the intensive studies. NOAA operates the wet/dry acid deposition network - AIRMoN and a U.S. ozonesonde network.

Air Quality Success Stories-"News You Can Use" from NOAA's Air Quality Research

The findings from NOAA's air quality research are changing the approach to defining clean air objectives, e.g., demonstrating that the "chemical diversity" across the U.S. implies that "one size does not fit all" in either air quality forecasting or in regulatory approaches to cost-effective air quality improvements. Among the findings:

  • In the Texas region: Leaks of reactive gases from the petrochemical refineries prevalent in the Houston region are a much, much larger factor in Houston's poor air quality than had been expected. These research results have altered the policy approach taken by Texas air quality managers, at a savings of 65,000 jobs and $10B for the state by the year 2010, and they are an example of key discoveries needed for an improved air quality forecasting service that is being developed by NOAA.
  • In the eastern U.S.: Smaller coal-fired electric-generating power plants produce more ozone pollution per unit of power generated than do larger power plants, a finding that has implications for future design decisions of the energy industry. Further, NOAA's research has demonstrated that the pollution per unit power also depends on the ambient chemical background of the air in the region of the power plant, and therefore the location of the power plant is a factor.
  • In the New England region: Nighttime chemical processes, as well as coupling between land and offshore processes, are more important to the region's air quality than previously thought. Their incorporation into air quality prediction models will lead to improved air quality forecasts for New England.


Technicians adjust instruments used for measuring air quality

NOAA scientists conduct experiments to study the reactions and properties of atmospheric gases and particles that are important in air quality.


P3 aircraft, NOAA ship Ron Brown involved in New Englans Air Quality Study

NOAA's P3 aircraft and the Ronald H. Brown research ship both were involved in an extensive air quality study in New England states 2002-04.


Houston skyline shrouded in smog

Downtown Houston skyline is obscured by air pollution.


smoke plume from a refinery

Refinery plumes like this contribute to Houston's air quality.

NOAA Research programs that focus on Understanding Air Quality

Air Resources Laboratory
Physical and numerical studies on the transport, dispersion, transformation, and removal of trace gases and aerosols relevant to air quality, leading to the development of air quality simulation models.

Earth System Research Laboratory (ESRL)

Chemical Sciences Division
Field, laboratory, and diagnostic modeling analyses to determine the chemical and dynamical processes associated with air quality in urban and rural environments

Global Monitoring Division
Measurements of ozone and ozone profiles, carbon monoxide, and dust and soot at several locations around the globe to assess baseline air quality.

Physical Sciences Division
Development and application of remote-sensing methods to observe and understand atmospheric air quality.

Global Systems Division
Research to develop better techniques for observations, data assimilation, and operational forecast models, including the operation of the demonstration wind profiler network and the development of models for the forecasting of air quality.

Pacific Marine Environmental Laboratory
Field studies and analyses of aerosols and trace gases in the marine environment and their effects on air quality in coastal regions.



Additional Related Information

Resources (NOAA's Air Quality Toolbox)

Air quality observations:

Measurement capabilities: