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Atmospheric Sciences & Global Change Division
Research Highlights

April 2013

Atmospheric Bit Players Take Stage

Influence of particles on regional water cycle and climate over California

LA smog and highway
As part of smog and pollution, atmospheric aerosols are noticeable. Our atmosphere is filled with these tiny bits of solid and liquid particles whether we see them or not. Understanding how they affect our water cycle and climate will help regional planners better gauge the effectiveness of emissions controls. Photo courtesy of Wikimedia Commons. Enlarge image.

Results: On the atmospheric stage, aerosols are bit players. Identifying each one and their role as change agents was the goal of researchers from Pacific Northwest National Laboratory, Colorado State University and the California Air Resources Board. For the first time, the researchers identified individual types of particles and their relative contribution to influence seasonal warming and cooling effects at the top of the atmosphere over California. Overall, carbon particles contributed up to 95 percent of the total warming throughout the seasons.

Why It Matters: Tiny atmospheric particles such as dust, chemicals and compounds are released from fossil fuel burning and natural sources. These particles can affect visibility, human health and the climate. With a better understanding of how each particle affects the atmosphere, scientists can help assess the success of regional emissions controls of human-caused particles. Of concern in this research was how specific particles directly affect the energy balance over California. The team's use of a popular meteorological-chemistry model to perform this baseline assessment promises to improve understanding of how regional controls limit pollution and other emissions will impact the water cycles and the climate.

Methods: Using the Weather Research and Forecasting model with coupled chemistry (WRF-Chem), the research team showed the model's capability to diagnose the direct radiative forcing of individual aerosol species. They ran the WRF-Chem simulations at a relatively high horizontal resolution of 12 kilometers covering California. The team evaluated model simulations with various datasets of meteorological and aerosol field measurements during 2005 and 2008.

The research team distinguished each particle type by chemical make-up and identified the amount of warming or cooling each particle is responsible for arranged by season and spatial distribution in the atmosphere. Overall, at the top of the atmosphere (TOA), the total aerosol direct radiative effect through all seasons was cooling with sulfate as the largest contributor in winter and summer. Elemental carbon aerosols and dust combined contributed to a TOA warming effect.

What's Next? Researchers will be working to understand the impact of aerosol particles to change the energy balance of the climate and how emission controls could abate those impacts on the regional climate. This understanding will help guide future emission control strategies.

Acknowledgments:

Sponsors: This work was supported by the California Air Resources Board (CARB) and the U.S. Department of Energy's (DOE's) Office of Science Regional and Global Climate Modeling Program. The study used computing resources from the National Energy Research Scientific Computing Center (NERSC) supported by the U.S. Department of Energy Office of Science, and PNNL's Institutional Computing.

Research Team: Chun Zhao, L. Ruby Leung and Richard C. Easter at PNNL; Jenny Hand at Colorado State University; and Jeremy Avise from the California Air Resources Board.

Reference: Zhao C, LR Leung, RC Easter, JL Hand, and J Avise. 2013. "Characterization of Speciated Aerosol Direct Radiative Forcing over California." Journal of Geophysical Research 118(5) 2372-2388. DOI:10.1029/2012JD018364.


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