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SUMMER WEATHER CAN PROMOTE POOR AIR QUALITY –
NOAA’S AIR QUALITY FORECAST GUIDANCE HELPS PREDICT IT

Weather and air quality graphic.May 14, 2007 — In many parts of the country, the arrival of summer signals the start of air pollution season. Fortunately, the NOAA National Weather Service’s air quality forecast guidance, produced in partnership with the U.S. Environmental Protection Agency, helps provide air quality forecasters and the public with information on predicted air quality conditions they need as they plan their daily activities.

NOAA’s involvement in air quality forecasting stems from the fact that air quality and weather go hand in hand. Weather can promote both the formation or degradation of various airborne pollutants and can disperse/transport them from one part of the country to another, thus making air quality a national issue.

“You can not accurately predict air quality without taking into account weather — and that is exactly what NOAA’s air quality forecast guidance does,” said Paula Davidson, manager for the NOAA National Weather Service’s Air Quality Forecasting program in Silver Spring, Md. “Measuring air pollution alone does not tell you very much about how it will change over the next few days, but by taking into account meteorological conditions such as wind, temperature, humidity, precipitation and cloud cover you gain a much better understanding of how and why air quality varies day to day.”

Ghent Power Plant, in Ghent, Ky., taken aboard a NOAA hurricane hunter aircraft in 1999.Benefits of Air Quality Forecasting
Air Quality forecasting is especially important to those who are most susceptible to air pollution. (Click NOAA aerial image for larger view of the Ghent Power Plant, in Ghent, Ky., taken aboard a NOAA hurricane hunter aircraft in 1999. Click here for high resolution version. Please credit “NOAA.”)

“For many individuals — especially sensitive groups including children, the elderly, and those who suffer from asthma and other respiratory/cardiovascular problems — knowing forecast levels of pollution can make a significant difference in the quality of their lives and how they plan their daily activities,” said Scott Jackson, environmental scientist at EPA's Office of Air Quality Planning and Standards in Research Triangle Park, N.C. “Those susceptible to poor air quality may need to modify their behavior and take precautionary measures, like limit strenuous outdoor activities, to protect themselves when Air Quality Index levels are high.”

WHAT YOU CAN DO TO MAKE THE AIR CLEANER?

You can help reduce pollution in your community by following these EPA-recommended guidelines:

  • Choose a cleaner commute — share a ride to work or use public transportation.
  • Combine errands and reduce trips.
  • Delay using gasoline powered lawn and garden equipment until later in the day or wait until days when the air quality is better, or avoid using them altogether.
  • Avoid burning leaves, trash and other materials.
  • Get regular car engine tune ups and replace your car's air filter and oil regularly.
  • Change spark plugs on recommended maintenance schedule.
  • Limit engine idling.
  • Reduce fireplace and wood stove use.

High concentrations of fine particles in the air and ground-level ozone cause respiratory and cardiovascular problems, contributing to tens of thousands of premature deaths annually. However, it has been estimated that for each one percent reduction in adverse health impacts that air quality forecasting could provide, more than one billion dollars could be saved every year.

Weather’s Impact on Air Quality
Air quality results from complex chemical and spatial interactions between many variables in the atmosphere, as well as the direct emission of both natural and man-made pollutants into the air. As a result, air quality varies widely depending on your local topography, how much air pollution is emitted or carried into your community, and by weather conditions.

“There is both cold-versus-warm season air quality and east-versus-west air quality,” said Clinton MacDonald, manager/air quality forecaster at Sonoma Technology, Inc. in Petaluma, Calif., and a contractor working with NOAA on air quality issues. “Although both the East and West coast experience ozone pollution in the summer months, particle pollution is interestingly absent for many western states in the summer because the type of fossil fuels burned in this region of the county release less sulfur containing compounds. In the winter, however, particle pollution returns to the western states in the form of smoke from wood-burning stoves, and other particles formed from emissions of ammonia, nitrogen oxides (NOx), and volatile organic compounds (VOCs).”

Ironically the same weather conditions that draw us outside in the summer (sunny skies, warm temperatures, low humidity and light winds) also promote air pollution and make it stagnate. Sunlight and heat, for example, promote ozone formation, as well as particle pollution. Conversely, weather conditions that make us want to stay inside (precipitation, cold temperatures and strong winds), clear pollutants from the air.

Image showing air quality forecast guidance during Hurricane Ophelia in 2005. As you can see from the image of Hurricane Ophelia to the right, strong winds and rain clear away poor air quality, while airborne pollutants can accumulate on the leading edge/peripheral feeder bands where the skies are clear and winds act to trap pollutants. (Click NOAA image for a larger/animated view of air quality forecast guidance during Hurricane Ophelia in 2005. Please credit “NOAA.”)

“Forecasting air quality for any area when a hurricane — or the remnants of a hurricane — is approaching can be tricky,” said Bill Murphey, chief meteorologist with the Georgia Department of Natural Resources. If a hurricane comes up from the Gulf of Mexico into Georgia, it can actually help to clear out air pollution from the area. But if the hurricane is moving up the Atlantic coast and you are on the subsident (or dry air) side of the tropical system, you often see an increase in air pollution — especially ground-level ozone.”

Weather can also affect how quickly pollutants move or are dispersed away from an area. Normally, pollutants rise or blow away from their sources without building up to unsafe levels. But imagine what would happen if the air became trapped and built up to unhealthy levels. This happens when winds are unusually light or during an inversion, when warm air moves in over the top of cold or cooler air, pinning it and airborne pollutants against the ground. Inversions can also occur on clear summer nights and can affect the next day's ground-level ozone concentrations.

“Geography can also affect air pollution. Mountain ranges surrounding a valley, such as those in southern California, can prevent pollution from dispersing,” said Bill Ryan, air quality forecaster and faculty research assistant at Penn State University in University Park, Penn. On the other hand, pollution is much more easily transported across state boundaries in the Midwest and East coast where the terrain is flatter and less complex.”

Same view on a smoggy day (pictured above) compared to clear day after cold weather front moved through (pictured below). Major Airborne Pollutants

“Ground-level ozone and particle pollution are the two main pollutants that are forecast and reported with the Air Quality Index,” said Jackson.

Ground-level ozone forms when two key pollutants, NOx and VOCs “cook in the sun” at warm temperatures. Ozone also exhibits a relatively consistent diurnal (daily) pattern since it forms throughout the day and slowly breaks down in the evening when the sun goes down.

Ozone can also be transported easily by the wind from one location to another making it a poor air quality concern to not only urban areas, but also surrounding suburban and rural areas.

Particle pollution, on the other hand, can either be directly emitted (e.g., smoke from a wood stove) or generated when gases and/or other aerosols react in the air. Nitrogen oxides and sulfur dioxides contribute to particle formation.

These ozone and particle-forming pollutants come from a wide variety of sources, including automobiles, power plants and industries. Natural sources also contribute — wildfires and volcanoes contribute to particle pollution, while trees and other vegetation can contribute to both particle and ozone pollution.

Sample air quality forecast guidance.NOAA’s Air Quality Forecast Guidance
NOAA’s air quality forecast guidance, produced twice a day from the NOAA National Centers for Environmental Prediction in Camp Springs, Md., helps local air quality forecasters by providing detailed hour-by-hour predictions, at high spatial resolution, of ground-level ozone across their communities. State and local air quality forecasters in more than 300 cities nationwide, use NOAA’s air quality forecast guidance and real-time weather and air quality observations to make forecasts. (Click NOAA image for larger view of sample air quality forecast guidance. Click here for high resolution version, which is a large file. Please credit “NOAA.”)

Unlike previous air quality forecasts that were worst-case, next-day air quality forecasts for a single city based on simple statistical techniques, NOAA’s air quality forecast guidance gives information for those in cities and suburbs alike, for all hours of the day and night.

Sample smoke forecast guidance. "A new tool for air quality prediction is NOAA's recently implemented Smoke Forecast Tool. Like NOAA’s ground-level ozone forecasts, this tool improves forecasters’ ability to predict the onset, severity and duration of smoke particle pollution in the air we breathe," said Davidson.
"This tool takes into account the smoke from burning fires detected in NOAA satellite imagery and its interaction with local and regional weather conditions."

Smoke particles contribute to the total mix of particle pollutants, and near fires they can become the dominant contribution to particle pollution. A striking example can be seen in the figure to the right, where smoke from wildfires in Georgia and Florida, interacted with Tropical Storm Andrea off the coast of Florida on May 10, 2007 (the forecast is for May 11). (Click NOAA image for larger view of NOAA's smoke forecast for May 11, 2007. Please credit “NOAA.”)

Because particle pollution is responsible for as many as 40,000 premature deaths each year, knowing when and where to expect harmful concentrations of smoke particles will help people to take steps to limit their exposure.

Relevant Web Sites
NOAA National Weather Service Air Quality Program

Understanding Air Quality

NOAA's Weather and Air Quality Research

NOAA's Program Charter for Air Quality

Air Quality Forecast Guidance Capabilities Fact Sheet

Media Contact:
NOAA National Weather Service Public Affairs, (301) 713-0622
Article by Julie Bedford (Editor, NOAA Magazine)