UM Rosenstiel School of Marine and Atmospheric Science professor Elliot Atlas recently returned from the two-month long CONTRAST (Convective Transport of Active Species in the Tropics) field experiment in the western Pacific Ocean. The research study focused on understanding the climate impact of trace gases transported from the ocean surface, up through a chimney of clouds and into the upper atmosphere.
Atlas, a professor of atmospheric chemistry, was a co-principal investigator of the first-of-its-kind National Science Foundation-funded research project into the chemistry of the tropical atmosphere.
Atlas is interested in trace gases that are linked to the formation and destruction of ozone in different layers of Earth’s atmosphere. In the upper part of the atmosphere, known as the stratosphere, ozone absorbs much of the harmful UV radiation coming from the sun. In the lower atmosphere, the presence of ozone is critical to facilitate the natural processes that cleanse the air of harmful pollutants. In the region where the lower and upper atmosphere meet, ozone acts as a greenhouse gas and its abundance can be linked to global climate change.
The thickness of the ozone layer varies worldwide, being smaller at the equator and bigger near the poles. The ozone layer has been depleted in recent years due to large quantities of man-made compounds, including the most well known, the aerosol sprays containing CFCs.
One question Atlas and his co-investigators Ross Salawitch from the University of Maryland and Laura Pan from the National Center for Atmospheric Research (NCAR), are trying to answer is, “what controls the abundance and variation of ozone in the atmosphere?”
To get closer to the answer, the CONTRAST team took to the sky to study the chemistry of clouds half a world away – in Guam. Understanding how atmospheric gases contribute to ozone abundances, and therefore Earth’s overall radiation budget from the sun, is critical for scientists to improve global climate change models.
“When you press on one side of the climate system, you get a response somewhere else,” says Atlas, explaining how seemingly different environments are linked in the global climate system.
A unique cluster of convective clouds – a virtual global chimney – forms over the western Pacific Ocean and is particularly intense during the winter in the Northern Hemisphere. The tropical chimney is key to determining the chemical composition of the air entering the stratosphere. Huge clusters of thunderstorms feed heat and moisture as well as gases and particles into the upper atmosphere and eventually into the stratosphere, where they can influence climate on a global scale.
Of particular interest to Atlas and his UM-based research team is the role of chemicals containing bromine. Bromine-containing chemicals are emitted into the atmosphere from two distinct sources – a man-made source, which include compounds commonly used in fire extinguishers and can remain in the atmosphere for decades, and a natural source of short-lived compounds produced by tiny marine organisms in the ocean.
The bromine component of these chemicals can rapidly react with ozone as the compounds decompose in the atmosphere. Man-made bromides leave long-lived fingerprints that can be easily identified. What UM Rosenstiel School scientists are investigating are the poorly understood natural bromine concentrations from the ocean that is lofted into the atmosphere through the tropical chimney.
Atlas, and his UM research team, which included post-doctoral researcher Maria Navarro and research fellow Valeria Donets, took to the sky to study the trace gases in the atmosphere that are produced in high amounts by marine organisms in the warm tropical waters of the western Pacific.
“We want to know what happens to the bromine contained in gases from marine organisms when they are moved by clouds from the near the ocean surface up to the boundary of the stratosphere, over 9 miles up,” says Atlas.
To collect bromine-containing gases, Atlas and colleagues built a specially designed instrument to fly onboard the NSF’s Gulfstream G-V aircraft during the 16 eight-hour CONTRAST flights. The aircraft flew at an altitude ranging from 0.5-15 km (0.2-9 miles), well above the limits of commercial airplanes, during January and February of 2014. The high altitude capabilities of this aircraft allowed the large team of scientists and engineers from multiple universities and research organizations participating in the project to study a critical part of the upper atmosphere that was unreachable by previous research aircraft.
To study the various chemical and physical components of the chimney cloud and the surrounding air, the aircraft was outfitted inside and out with state-of-the-art equipment that measure the many gases and air particles in the skies as the aircraft flew through the atmosphere, along with other data to understand the state of the atmosphere during the flights. During each mission, researchers at the shore-based operation center on Guam watched as data streamed back in real time and they communicated with colleagues onboard the aircraft to make spur-of-the-moment decisions about where additional sampling should take place. While instruments on the aircraft were making real-time measurements, trace gases were also being collected in airtight canisters for further in-depth analysis back in Atlas’ lab.
Now that the scientists have returned to their home bases, the data collected during the mission will be further analyzed and used to test how well current climate models depict cloud convection processes and the chemical composition of the tropical atmosphere, with a goal of improving how climate models predict future climate changes.
CONTRAST was conducted in collaboration with two other field experiments to take a comprehensive look at the entire region – the UK-led CAST (Coordinated Airborne Studies in the Tropics) experiment flew an instrument-laden aircraft to perform detailed studies in the atmosphere from near the ocean surface up to 6 km (3.7 mi), while the high-altitude ATTREX (Airborne Tropical Tropopause Experiment) mission using NASA’s Global Hawk unmanned drone studied the chemistry and physics of the atmosphere from 14-19 km (9-12 mi) altitude. The NSF G-V aircraft overlapped the study regions of the other two aircraft and sampled near the altitude of the outflow of the tropical cloud chimney.
“These combined aircraft measurements will provide an unprecedented description of the tropical atmosphere, from the ocean surface to the lower stratosphere, which will ultimately improve our current understanding of the atmosphere and our ability to make predictions about the role of atmospheric chemistry and tropical convection in a future climate,” said Atlas.