Ocean-air chemistry gets clearer and cloudier
CU team finds first conclusive evidence of climate-relevant gases over the remote Pacific Ocean, but why those gases exist where they do is a mystery
or the first time, the climate-altering gases glyoxal and iodine oxide have been confirmed to exist over the remote Pacific Ocean. The findings of the University of Colorado team are surprising and potentially significant.
They are surprising because there is no known explanation for why these short-lived gases would exist so far from land. And the findings are potentially significant because the two gases can form aerosols, which have a net cooling effect on the planet and whose behavior is not well understood.
The two gases are not included in climate models encompassing the ocean.
Rainer Volkamer, a CU assistant professor of chemistry and biochemistry and leader of the research group that confirmed the existence of glyoxal 2,000 miles from land, notes that much discussion about climate-altering gases concerns long-lived compounds such as carbon dioxide, which can remain in the atmosphere for centuries.
Carbon dioxide’s absorption of longwave radiation and emission of heat is basic physics. But with respect to climate, Volkamer says, “The role of chemistry is yet to be fully understood.”
A 2007 Summary for Policy Makers of the Intergovernmental Panel on Climate Change noted that aerosol dynamics remain “the dominant uncertainty” in climate models.
Glyoxal, a reactive molecule, exists an average of about two hours in the air. Climate models do not predict any glyoxal over the remote open ocean.
Yet Volkamer’s team found “unambiguous” proof that glyoxal exists over the remote Pacific in concentrations up to 120 parts per trillion. Its existence in this location is a mystery.
About 30 percent of glyoxal is produced over land by plants that emit isoprene, which can be transformed into glyoxal in the presence of oxygen. But isoprene concentrations in the remote Pacific are between 2 and 35 times lower than they would need to be to produce the levels of observed glyoxal.
About 14 percent of airborne glyoxal comes from human activities such as manufacturing. Another 6 percent comes from fires. The source of half of all glyoxal formation over continents is unknown. And the source of glyoxal over the ocean is unclear. That is one reason Volkamer’s discovery is potentially significant.
Still, it is puzzling. The glyoxal he observed could not have been blown from the land by wind. It would take about a week for the wind to blow the gas 2,000 miles over the ocean. That’s about 84 times longer than the gas would exist.
Further, glyoxal is so highly water-soluble that it is “tough to get out of the ocean,” Volkamer says.
“The source of the glyoxal as well as of (iodine oxide) is not currently understood,” a 2010 article by Volkamer and his colleagues notes. “We don’t have an understanding of where the glyoxal is coming from,” Volkamer emphasizes in an interview.
What they do know, though, is that climate dynamics involve atmospheric chemistry, the understanding of which is still evolving. Aerosols are tiny, airborne solid and liquid particles. When enough aerosols are aloft, air can appear hazy.
As Volkamer notes, aerosols can cool the planet by reflecting a portion of the incoming sunlight back into space and by potentially increasing cloud cover.
Aerosols can be formed by chemical reactions. Volkamer notes that reactive chemical components modify the aerosols’ likelihood of bonding with water-vapor molecules.
Certain gases lead to the growth of larger aerosol particles, which mask some of the warming effect of greenhouse gases, he adds. “Chemistry is at the interface of these reactions and climate effects.”
As for glyoxal and iodine oxide, “Here we have these reactive gases that have the ability to form aerosols, and we need to do more research to understand the relationship between aerosols and cloud formation.”
Volkamer underscores the need for long-term measurements of glyoxal and iodine oxide over the remote ocean. While his team’s findings are a first, they are essentially a snapshot in time. Global levels of carbon dioxide and other greenhouse gases, on the other hand, have been carefully monitored for more than five decades.
Volkamer’s observations were made with a ship-borne device called the CU Ship Multi-Axis Differential Optical Absorption instrument. That instrument was built in the Volkamer lab and was tested on top of Folsom Field’s skyboxes on the CU-Boulder campus.
As it happened, the U.S. Research Vessel Ron Brown was conducting a field experiment funded by the National Science Foundation in the Eastern tropical Pacific Ocean between October 2008 and January 2009, and Volkamer was allowed to affix his instrument to the ship during its journey.
The NOAA Research Vessel Ronald H. Brown is shown with an inset of the Volkamer team's SMAX-DOAS instrument, which was built and tested at CU. Photo courtesy of Rainer Volkamer.
Before Volkamer’s confirmation of these potentially climate-relevant gases, satellite observations had shown some (but inconsistent) evidence that glyoxal might exist over the remote ocean. The satellites’ data were not conclusive, however, and different satellites gave different answers as to the glyoxal abundance for reasons that are still to be understood.
Volkamer’s work was funded by the NSF and by lab-startup funds from the university. Volkamer is also a fellow in the CU Cooperative Institute for Research in Environmental Sciences.