SCIENCE

Scientists from the Department of Energy's Pacific Northwest National Laboratory will present their research at the 2010 American Geophysical Union Fall Meeting, which runs Monday, Dec. 13 through Friday, Dec. 17 at the Moscone Convention Center in San Francisco.

Saharan dust makes for wetter African nights, drier days

Understanding dust's impact can help with global climate change predictions

The massive Saharan Desert brings copious amounts of dust to African skies. The dust blocks sunlight and leads to more nighttime rainfall and drier days during the monsoon season, according to PNNL climate scientist Chun Zhao. Zhao and colleagues used a regional climate model to examine how West Africa's precipitation and temperatures might differ during the monsoon season if the Sahara didn't produce dust. The hypothetical dust-free scenario had up to 25 percent more rain during the late afternoon than what actually falls. On the flip side, real-world Africa has more rain during the evenings and early mornings. They learned that dust particles in the air partially block sunlight and absorb its heat during the day. In the nighttime, that heat radiates from the sky to the land below, which then warms up the surface and makes conditions ripe for nocturnal precipitation. This knowledge could help predict climate change's future impacts in West Africa and elsewhere. 

A13E-0257: Radiative forcing of Sahara dust and its impacts on the hydrological cycle in the West African monsoon season, Monday, Dec. 13, 2-5 p.m., Poster Hall, Moscone South. http://www.atmos-chem-phys-discuss.net/10/27185/2010/acpd-10-27185-2010.html

SPLAT unearths complex view of airborne particles

Measuring individual particles instead of the average reveals a complex landscape

Climate researchers trying to characterize aerosol particles — tiny bits of organic molecules, sulfate, dust, soot and more — are limited to measuring averages, missing the fact that particles come in many different colors and shapes. SPLAT, an instrument partly developed in EMSL, DOE's Environmental Molecular Sciences Lab at PNNL, can determine the size and composition of individual particles ranging from 50 nanometers (about the size of a small virus) to 3 microns (at least 10 times thinner than the thinnest hair). In Sacramento, Calif., PNNL's Josef Beranek and colleagues used SPLAT for a month to measure the sizes of 195 million particles and the chemical composition of a 10-million-particle subset. They found that particles in Sacramento, though very small, change in size and composition throughout the day in a nearly reproducible pattern. Also, at any point in time, the atmosphere holds a complex mixture of them. The researchers saw particles with organic chemicals mixed with sulfate, from wood-burning, with soot and sea-salt both fresh and aged, and different types of dust. Because particles with different chemistries affect the climate differently, the more intricate view should improve computer models of the atmosphere. 

A131-03: The Diurnal Cycle of Particle Sizes, Compositions, and Densities observed in Sacramento, CA during CARES Field Campaign, Monday, Dec. 13, 2:10 p.m., Moscone West, Room 3002. NOTE: Alla Zelenyuk will be speaking in place of Josef Beranek 

Focus on tiny aerosols reveals bigger climate picture

Mini climate model-within-a-model explains cloud behavior

Typical global climate models have difficulty showing how clouds and aerosols - tiny natural and manmade bits of dirt, soot and other particles in the air - influence the Earth's climate. Such models primarily use grids that divide the atmosphere into 100-kilometer square chunks of air. But most clouds are less than 10 kilometers in size, making them small blips on the larger maps of global models. PNNL climate scientist Steve Ghan will present the Multi-Scale Modeling Framework Approach, which zooms in on clouds by creating miniature computer models of the water content and updraft winds within clouds. These mini models more accurately show how aerosols influence clouds by acting as seeds for cloud droplets and how clouds wash aerosols from the sky. The mini model is then inserted into each 100-kilometer cell of a global climate model.  A national research team led by PNNL used the approach to more accurately predict how much aerosols scatter and absorb sunlight, affect cloud droplet formation and impact how much light clouds reflect. Observations of Arctic air, for example, show the PNNL model simulates aerosol concentrations about 10 times more accurately than a traditional climate model. This suggests that the effect manmade aerosols have on climate change can be more realistically simulated than it is with current global models. 

A22C-08: Cloud-Aerosol Interactions in a Multiscale Aerosol Climate Model, Tuesday, Dec. 14, 11:56 a.m., Moscone West, Room 3006.

STOMP on risk of escaping carbon dioxide 

PNNL model could help determine the likelihood of leaks from emissions stored underground

A new reference table may give researchers a way of estimating the likelihood that carbon dioxide emissions stored underground will leak.  Scientist Zhangshuan (Jason) Hou and his colleagues at PNNL used the subsurface transport over multiple phases, or STOMP, simulator to develop the table, which takes the form of a simplified equation called the generalized additive model, or GAM.  To use the model, scientists gather data measurements from at least three, but as many as five, "dimensions" from a particular site, such as shale seal thickness, porosity and permeability of shale seal and sandstone reservoir, and plug them into the equation. The resulting outcome of the equation is the prediction of the percentage of leakage expected over a particular observation time period, together with the uncertainty associated with the estimate. The research was funded by the U.S. Department of Energy's Office of Fossil Energy through the National Risk Assessment Partnership.

NG23A: Evaluating the impacts of caprock and reservoir properties on potential risk of CO₂ leakage after injection, Tuesday, Dec. 14, 1:40 p.m. Poster Hall, Moscone South.

Tags: Energy, Environment, Fundamental Science, Emissions, Carbon Capture and Sequestration, Climate Change, Aerosols

EMSL, the Environmental Molecular Sciences Laboratory, is a national scientific user facility sponsored by the Department of Energy's Office of Science, Biological and Environmental Research program that is located at Pacific Northwest National Laboratory. EMSL offers an open, collaborative environment for scientific discovery to researchers around the world. EMSL's technical experts and suite of custom and advanced instruments are unmatched. Its integrated computational and experimental capabilities enable researchers to realize fundamental scientific insights and create new technologies. Follow EMSL on Facebook.