Results showing how pure a key component of climate really is
Lynn Russell, an atmospheric sciences professor at Scripps Institution of Oceanography, UC San Diego, presented findings at the American Geophysical Union (AGU) Fall Meeting from a multi-institutional study that considered what constitutes pristine marine aerosols and where they actually exist.
Aerosols produced naturally during wave breaking include minerals such as salt and bits of organic matter. They contribute to climate processes when they are ejected from the ocean into the atmosphere. There they play a large role in the formation of clouds and precipitation and in governing where solar energy is directed. The complex process is considered by scientists one of the important unknowns in attempts to simulate and predict climate phenomena. Russell said that a fundamental step is to determine what the oceans contribute naturally to atmospheric processes versus what they contribute when human sources of aerosols – ranging from ship exhaust to pollution originating on land – are added to the mix.
“We have chemically characterized the natural sources of organic components that can inform future studies of one of the most important unknowns in climate,” Russell said.
Russell discussed the results of a study published in November in the Journal of Geophysical Research in the AGU poster session “Where and What is Pristine Marine Aerosol?” Dec. 18.
To predict climate change, global climate models need to contain not only inputs reflecting the increases in greenhouse gases since preindustrial times but also the changes in aerosol concentrations and composition, the researchers said. Because the air in marine regions is influenced and polluted by shipping and urban emissions, it is challenging to sample air that is representative of pristine marine conditions. Such conditions are characterized by the sea spray particles and gaseous emissions from the ocean surface, which include components from the organisms that inhabit the surface waters. The researchers have developed a new, more accurate way to discriminate between these marine sources and those associated with the products of fossil fuel combustion in urban areas and from shipping activities.
Amanda Frossard, a former Scripps graduate student in Russell’s group now at UC Berkeley, compared actual aerosol measurements with model simulations indicating what the oceans would be expected to produce naturally.
Particularly notable in the comparison was the addition from human sources of a class of chemical compounds known as alkanes. These compounds can be a by-product of ship travel, of fossil fuel use in motor vehicles on land, or the burning of plant material. Because these compounds can also be produced naturally and because they so quickly mix with naturally produced aerosols in the atmosphere, teasing out natural sources from human sources has been difficult for scientists. As a consequence, some measurements that have been used to constrain models may have been misinterpreted. The chemically specific measurements of organic components made in this study provide a better characterization of the marine contribution and of its regional and seasonal differences.
With a better understanding of actual pristine marine aerosol contributions, researchers are better able to simulate pre-industrial atmospheric aerosols and that allows them to better constrain recent changes in climate, Russell said.
As far as where pristine aerosols could be found in nature today, the researchers concluded that there are few places where marine samples are truly pristine. Even samples from remote ocean regions in the Southern Hemisphere contained human-contributed chemicals.
Besides Russell, contributors to the study “Sources and composition of submicron organic mass in marine aerosol particles” referenced in her presentation include lead author Amanda Frossard of Scripps, Susannah Burrows of Pacific Northwest National Laboratory, Scott Elliott of Los Alamos National Laboratory, Timothy Bates and Patricia Quinn of the University of Washington, and Patricia Quinn of NOAA Pacific Marine Environmental Laboratory.