SAN FRANCISCO — With the help of satellite instruments and airborne sensors, NASA scientists are continuing to uncover clues to explain the complex role atmospheric aerosols play in global climate change.
Still, they lament the loss of the space agency’s Glory climate monitoring satellite with its Aerosol Polarimetry Sensor, which was designed to help researchers distinguish naturally occurring particles such as salt and mineral dust from pollution produced by burning fossil fuels.
NASA officials, including Hal Maring, the former Glory program scientist at NASA headquarters in Washington, were devastated when the $424 million Glory spacecraft was destroyed during the failed March 2011 launch of an Orbital Sciences Corp. Taurus XL rocket. “The real advantage of Glory was that it was going to give us more direct measurement of aerosol composition,” Maring said, adding that various types of aerosols have different impacts on clouds, precipitation and the amount of heat radiating from and reflected back toward Earth.
In spite of that setback, scientists have been able to piece together some of that information using existing satellite, airborne and ground-based sensors. A recent study determined, for example, that nearly half of the aerosol particles temporarily suspended above North America originated in other parts of the world. The study, which was the first to use data drawn from satellites to estimate the number and type of atmospheric particles, also found that most aerosols over North America were located high in the atmosphere and were comprised of dust instead of pollution.
“In some ways that is good news,” said Lorraine Remer, an atmospheric scientist at the University of Maryland, Baltimore County and co-author of the study. It allays some of the concern among policymakers that rapidly growing Asian nations could harm North American air quality by exporting pollution. In other ways, the finding is troubling, Remer said, because it shows that even if industrial nations significantly reduce pollution, the loss of fertile agricultural regions due to drought and deforestation will continue to produce atmospheric aerosols.
The study, published Aug. 3 in the journal Science, relied on the Moderate Resolution Imaging Spectroradiometer flying on NASA’s Terra and Aqua Earth observation satellites and the Cloud-Aerosol Lidar with Orthogonal Polarization onboard NASA’s Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation spacecraft — also known as Calipso — to determine the origin and type of aerosol particles as well as their altitude, said Hongbin Yu, lead author of the study and an atmospheric scientist at the University of Maryland, College Park and NASA’s Goddard Space Flight Center in Greenbelt, Md.
A New Found Glory?
Glory’s Aerosol Polarimetry Sensor built by Raytheon Space and Airborne Systems of El Segundo, Calif., was designed to provide even more detailed information on aerosols. The instrument featured six telescopes designed to distinguish aerosols produced by human activity from those resulting from volcanoes, forest fires, sea salt, mineral dust and pollen.
Scientists remain eager to obtain that information because aerosols affect “weather and climate, air quality and health, and the biogeochemistry of our world,” said Maring, who continues to serve as a program scientist in NASA’s Earth Sciences Division. Unlike greenhouse gases, which are distributed throughout the atmosphere, aerosol concentrations vary widely. As a result, their impact on the environment is difficult to study without space-based sensors offering frequent, global observations. “Aerosols account for one of the greatest areas of uncertainty in scientific understanding of climate change,” Maring said.
NASA officials are evaluating the merits of building a new satellite polarimeter to replace the one lost on Glory, Maring said. “With a proven design in place, Raytheon stands ready to build a second Aerosol Polarimetry Sensor should NASA elect to do so,” Warren Flynn, Raytheon’s director of environmental sensing, said by email.
In the meantime, NASA is scheduled to send a lidar to the international space station in 2013 to assist in aerosol monitoring. The Cloud-Aerosol Transport System being developed by NASA’s Goddard Space Flight Center is designed to provide data on the location of aerosols in Earth’s atmosphere and the interaction between aerosols and clouds.
Scientists selected to support the Glory mission have refocused their attention on using data from existing satellite, airborne and ground-based sensors to study aerosols and their impact on the environment, Maring said. Some of those data come from satellites launched by NASA’s international partners. For instance, NASA scientists are obtaining aerosol data from an imaging radiometer and polarimeter, known as Polarization and Directionality of the Earth’s Reflectances, flying on the French space agency, CNES, Parasol microsatellite.
Like the Terra satellite launched in 1999 and Aqua satellite launched in 2002, Parasol is beyond its design life. Launched in 2004, Parasol dropped out of the afternoon constellation of international Earth observing satellites in 2009 because it was running low on propellant. Nevertheless, the spacecraft remains in orbit and continues to produce useful aerosol observations, Maring said Oct. 3.
To ensure that aerosol-monitoring programs continue when the current fleet of spacecraft retires, international space agencies are developing new missions. The European Space Agency plans to launch the Cloud Aerosol and Radiation mission, EarthCare, in 2015. The EarthCare spacecraft is expected to include four instruments to observe clouds, aerosols and their impact on the sun’s radiation: Atmospheric Lidar, Cloud Profiling Radar, Multispectral Imager and Broad-Band Radiometer. In addition, NASA is drafting plans for an Aerosol-Cloud-Ecosystems mission to be launched in approximately 2020, Maring said.