NCAR generates 48-hour forecasts of U.S. air quality

Experimental predictions can help decision makers and the public, accelerate new research

Sep 13, 2019 - by David Hosansky

The National Center for Atmospheric Research (NCAR) is now generating high-resolution, experimental, 48-hour forecasts of air pollutants across the contiguous United States. The predictions, which are freely available online, can help decision makers anticipate episodes of unhealthy air as well as accelerate research into the factors that influence air quality.

The system, which draws on observations of pollutants, weather forecasts, and advanced computer modeling, will complement existing operational air quality forecasts issued by the National Oceanic and Atmospheric Administration (NOAA). The NCAR forecasts are primarily for research purposes, but they are based on different techniques than those used by NOAA and can provide state and local officials who are trying to safeguard public health with a more complete picture of air quality.

"It provides decision makers and also the public with an additional piece of information," said NCAR scientist Gabriele Pfister. "If two forecasts tell you the same thing, that gives you more confidence. If they do not agree, this means that conditions are harder to predict but you should be prepared for the possibility of unhealthy air quality."

The forecast maps, publicly accessible on an NCAR webpage, show anticipated levels of ozone, particulates, and other damaging pollutants as well as near-real time measurements from Environmental Protection Agency Airnow sites. Users can view the pollutants at different heights in the atmosphere, they can view the entire United States or take a closer look on Colorado, and they can also focus on pollutants from fires. The forecasts are updated once a day and continuously compared to observations.

The work builds on a new forecasting system that NCAR has developed for New Delhi and other heavily polluted parts of northern India. The system can be readily adapted for other regions of the world as well.

Pfister and her colleagues say the forecasts, in addition to helping to protect the public, will support and advance research into air quality by providing scientists with daily examples of pollution levels across the country.

"Scientists can take the output, separate out different sources of the pollutants, and evaluate the forecasts in light of actual levels of pollutants," said NCAR scientist Rajesh Kumar.  "This is really useful for fingerprinting the sources of emissions."

The research for the system is funded by NASA and the National Science Foundation, which is NCAR's sponsor.

A major health and economic issue

Although meteorologists have long been able to forecast the weather days in advance, predicting air quality is more challenging. That's because air quality forecasts rely on accurate predictions of weather conditions (which affect air quality) as well as detailed assessments of ever-changing emissions of pollutants and how they evolve and move in the atmosphere.

Air pollution is a significant health and economic issue. Poor air quality in the United States causes as many as 60,000 premature deaths each year, and the annual costs of air pollution-related illnesses can be as high as $150 billion, according to NOAA estimates.

Accurate forecasts can enable vulnerable residents, such as those with asthma or pulmonary or cardiovascular diseases, to better protect themselves by planning ahead and limiting outdoor exposure on highly polluted days.

The NCAR forecasting system incorporates satellite and ground-based measurements of particles and gases in the atmosphere, as well as inventories of emissions from transportation, industry, and other human activities. This information is combined with forecasts of meteorological conditions and fed into a specialized NCAR-based atmospheric chemistry computer model known as WRF-Chem (the chemistry component of the Weather Research and Forecasting model), which then simulates air quality conditions over the next 48 hours.

Even though the system focuses on the United States, it incorporates observations and computer simulations of pollutants flowing into the country from outside regions, such as Asia, by incorporating global air quality predictions from the NCAR-based Whole Atmosphere Model. The system also has a highly advanced fire modeling component that simulates emissions from wildfires and prescribed burns, recreating their impacts on local and regional air quality as well as on atmospheric conditions such as cloud cover, which in turn influence levels of air pollution.

The NCAR team is continually evaluating the system and working on upgrades, such as improvements to the ways that observations are fed into the model.

NCAR has generated accurate forecasts in the past for specialized field experiments that deploy research aircraft to study atmospheric chemistry, Pfister said. By using similar technology to make the research forecasts every day, the scientists can help decision makers and the public, as well as other researchers.

"We are taking what we have already been doing for research campaigns and using it to benefit not just the specific campaigns, but everyone," Pfister said.  "This will provide important information now as well as lead to enhancements of air quality predictions in the future."

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