More Pollutants Could Remain in Atmosphere With Less Light Rain

New study shows effects of rainfall on pollutants vary by the severity of precipitation

Scientists from Scripps Institution of Oceanography at UC San Diego, Lawrence Livermore National Laboratory, and international collaborators have shown that an improved representation of drizzle rates leads to more pollution in the atmosphere. The research appeared January 11 in Nature Geoscience.

Atmospheric aerosols are of great climatic and environmental importance due to their effects on the Earth’s radiative energy balance and air quality. Aerosol concentrations are strongly influenced by rainfall through wet removal processes. In general, light rainfall is more effective at removing pollutants from the atmosphere than heavy rain. Global and regional climate models have been used to quantify potential impacts of aerosol concentrations on climate. However, most current climate models tend to produce too much light rain and too little heavy rain, which, in turn, underestimates the effects of aerosols on the climate.  

The team showed that rainfall intensity has profound impacts on aerosol mass (known as the aerosol burden), and light rain has a disproportionate control on it. By improving the representation of atmospheric convection, the light rain frequency in two state-of-the-art global climate models, the Department of Energy (DOE)’s Energy Exascale Earth System Model (E3SM) version1 and the National Center for Atmospheric Research Community Atmosphere Model version 5 (CAM5), is reduced. As a result, the aerosol burden is increased globally, especially over the tropics and subtropics.

“These new results help us understand the nature of aerosol wet removal by rainfall that is critical to aerosol-climate interaction and its impact on climate,” said Guang Zhang, a climate scientist at Scripps Institution of Oceanography and corresponding author of the study who organized the research.

The increased aerosols in the air would lead to more adverse effects on human health. Long-term exposures to particulate matters can elevate the risks of having cardiovascular and respiratory diseases, resulting in premature death, according to the U.S. Environmental Protection Agency health studies.

“The current models are too effective at washing out pollutants because they produce  too much light rain,” said Shaocheng Xie, one of the coauthors from Lawrence Livermore National Laboratory. 

Other Livermore researchers include Qi Tang and Hsi-Yen Ma. The Scripps portion of the research was funded by DOE’s Earth System Model Development and Analysis (ESMD) and Atmospheric System Research (ASR) programs. The Livermore portion of the research was funded by DOE’s E3SM project and the Cloud-Associated Parameterizations Testbed (CAPT) project.

This release was adapted from Lawrence Livermore National Laboratory.


About Scripps Oceanography

Scripps Institution of Oceanography at the University of California San Diego is one of the world’s most important centers for global earth science research and education. In its second century of discovery, Scripps scientists work to understand and protect the planet, and investigate our oceans, Earth, and atmosphere to find solutions to our greatest environmental challenges. Scripps offers unparalleled education and training for the next generation of scientific and environmental leaders through its undergraduate, master’s and doctoral programs. The institution also operates a fleet of four oceanographic research vessels, and is home to Birch Aquarium at Scripps, the public exploration center that welcomes 500,000 visitors each year.

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