The Science
Airborne organic particles play a critical role in Earth’s climate, public health, air quality, and hydrological and carbon cycles, but sources of solid organic particles in the atmosphere are poorly understood. A new study shows rain events are an unrecognized contributor to airborne soil organic particles.
The Impact
The findings suggest airborne soil organic particles could have important impacts on cloud formation and the absorption of solar radiation. Therefore, the study could be used to improve the accuracy of atmospheric models and to deepen our understanding of atmosphere-land interactions and how airborne organic particles influence Earth’s climate.
Summary
While sources of solid airborne organic particles have not been well defined, scientists have assumed soil organic particles primarily enter the atmosphere through wind erosion or human activities, such as agricultural tilling or harvesting. A new study challenges this widespread assumption by showing precipitation might be an efficient and yet unrecognized contributor to the formation of airborne soil organic particles. This discovery was made by a team of researchers from EMSL, the Environmental Molecular Sciences Laboratory; Lawrence Berkeley National Laboratory (LBNL); the University of California, Berkeley; and the University of Massachusetts, Amherst. The team was using a variety of chemical imaging approaches to study particles collected after rain events in the Southern Great Plains, Oklahoma, and after experimental irrigation. They used environmental focused ion beam and scanning electron microscopy (Quanta), environmental transmission electron microscopy and helium ion analyses at EMSL, a Department of Energy (DOE) national scientific user facility, and they used X-ray absorption spectro-microscopy analysis at the Advanced Light Source, a synchrotron facility at LBNL. After rain events, the team found that sub-micrometer solid particles with a chemical composition consistent with soil organic matter contributed up to 60 percent of atmospheric particles. Subsequent irrigation experiments showed intensive water impaction was sufficient to cause soil organic particles to eject from the surface of watered soils. In-depth studies of particle physical properties suggested they might have important impacts on cloud formation and absorption of solar radiation. Taken together, the findings suggest raindrop-induced formation of solid organic particles from soils may be a widespread phenomenon in ecosystems, such as agricultural systems and grasslands, where soils are exposed to strong, episodic precipitation events. The observations of solid airborne soil organic particles challenge our understanding of the sources and formation mechanisms of atmospheric organic particles, and suggest an additional source from atmosphere-land surface interactions.
Read related PNNL news release.
PI Contact
Alexander Laskin
EMSL/PNNL
alexander.laskin@pnnl.gov
Funding
This work was supported by the DOE Office of Science, Office of Biological and Environmental Research, including the Atmospheric System Research program; EMSL, a DOE Office of Science User Facility at Pacific Northwest National Laboratory (PNNL); Atmospheric Radiation Measurement, a DOE Office of Science User Facility; the Chemical Imaging Initiative of the Laboratory-Directed Research and Development Program at PNNL; the Advanced Light Source at LBNL, a DOE Office of Science User Facility at LBNL; and the Office of Basic Energy Sciences Condensed Phase and Interfacial Molecular Sciences program.
Publication
B. Wang, T.H. Harder, S.T. Kelly, D.S. Piens, S. China, L. Kovarik, M. Keiluweit, B.W. Arey, M.K. Gilles and A. Laskin, “Airborne soil organic particles generated by precipitation.” Nature Geoscience (2016). [DOI: 10.1038/ngeo2705]