SAN FRANCISCO — Twenty-five years after the international community forged an agreement to begin phasing out the use of ozone-depleting chemicals, space-based instruments are gathering evidence that the enormous hole in the protective layer of Earth’s stratosphere finally has stopped expanding and begun to stabilize.

Within the next 10 years, researchers hope to see evidence the hole is shrinking. 

“The ozone hole is being monitored carefully because the models tell us that we should soon start to see the turnaround,” said Glen Jaross, NASA research scientist at the Goddard Space Flight Center in Greenbelt, Maryland. “Everyone is looking for that turnaround.”

It takes four to five years for man-made chemicals, including chlorofluorocarbons and hydrochlorofluorocarbons, to rise to the stratosphere, where the sun’s ultraviolet radiation breaks down their chemical composition and releases chlorine, which destroys ozone molecules. Those chlorine atoms can continue to destroy ozone for years until atmospheric winds carry them down to the troposphere. As a result, it has taken decades for scientists to see evidence that the 1989 Montreal Protocol on Substances that Deplete the Ozone Layer is succeeding in decreasing levels of ozone-depleting gases in the atmosphere. 

Due to the slow pace of ozone destruction and recovery, researchers remain intent on using successive generations of space-based tools to obtain uninterrupted observation of atmospheric ozone levels. Those observations, which began in the 1970s with the Solar Backscatter Ultraviolet instrument onboard NASA’s Nimbus 7 satellite, continue with the Ozone Mapping Profiler Suite (OMPS) launched in October 2011 on the NASA-NOAA Suomi NPP spacecraft.

“OMPS extends the climate data record into the future so we can look at how the ozone layer is changing not just because of ozone-depleting chemicals but also because of climate change,” said Craig Long, a research meteorologist with the National Oceanic and Atmospheric Administration’s Climate Prediction Center.

NASA and NOAA officials say the OMPS instrument, built by Ball Aerospace & Technologies Corp. of Boulder, Colorado, is functioning well. The instrument was designed to operate for at least seven years. Researchers now hope it will continue to gather data for 10 years or more.

Its predecessor, the Ozone Monitoring Instrument, on NASA’s Aura Earth Observation Satellite launched in 2004, “continues to perform remarkably well despite a 2009 anomaly that has halved its spatial coverage,” Jaross said. 

OMPS features three hyperspectral instruments. Two are designed to peer down directly through Earth’s atmosphere. One nadir instrument measures the total amount of ozone in each column of air and another observes the vertical distribution of ozone in the middle and upper stratosphere. The third OMPS sensor, a limb profiler, makes observations at an angle to Earth’s surface, providing researchers with more detailed information on the vertical distribution of ozone in the upper troposphere and lower stratosphere.

NOAA officials still are calibrating all the OMPS instruments and developing algorithms to determine the best way to use the data they provide. “The limb profiler is so new we’re continuing to learn how to best use the information it provides,” Long said. 

Still, NOAA officials plan to begin using OMPS data in the next year. “It takes time to get those into our forecast models,” Long said. 

In addition to monitoring the Antarctic ozone hole, OMPS data will be used by the National Weather Service’s Climate Prediction Center in its daily forecasts of ultraviolet radiation intensity for major cities. 

Ozone levels also help to determine weather patterns. “Ozone, a greenhouse gas, retains heat,” Long said. “To get good monthly and seasonal forecasts we need to know ozone levels in the troposphere and stratosphere.”

Even as OMPS data begin to make their way into operational forecasts, NASA and NOAA officials are discussing plans to improve the resolution of the OMPS nadir mapper, which currently calculates total column ozone for ground pixels no smaller than 50 kilometers. Their goal is to decrease the size of each pixel to focus on squares of 17 kilometers or less. 

“That flexibility was designed into the OMPS instrument,” said Jaross, who is a member of NASA’s nadir ozone team. “We do not yet have official approval to make that happen, but we are working on it.”

Due to budget constraints, NASA and NOAA plan to include nadir instruments but not the limb profiler on the first Joint Polar Satellite System spacecraft scheduled for launch in 2017. The second Joint Polar Satellite System spacecraft is scheduled to carry the full instrument suite, Long said. 

The nadir-mapping instruments on the Joint Polar Satellite System-1 OMPS will offer 10-kilometer spatial resolution, Jaross said. That improved spatial resolution is likely to help researchers detect sources of sulfur dioxide, including volcanoes and coal-burning power plants. Greater spatial resolution also is likely to provide data on ash, dust and other aerosols in Earth’s atmosphere, Jaross said. 

The Joint Polar Satellite System-1 OMPS instrument also will gather data in a larger range of wavelengths than OMPS onboard Suomi. OMPS for Joint Polar Satellite System-1 features longer wavelengths to overlap with the shortest spectral channel of the Visible Infrared Imaging Radiometer Suite, a weather and climate sensor flying on Suomi and Joint Polar Satellite System-1, “possibly providing a direct comparison between OMPS and [Visible Infrared Imaging Radiometer Suite] measurements,” Jaross said.