Amazon Study Reveals that Rainstorms Transport Atmospheric Particles Essential for Cloud Formation
Tracking atmospheric particles in a pristine environment will help scientists understand the impact of industrial aerosols on climate.
Understanding how tiny particles emitted by cars and factories affect Earth’s climate requires accurate climate modeling and the ability to quantify the effects of these pollutant particles vs. particles naturally present in the atmosphere. One large uncertainty is what Earth was like before these industrial-era emissions began. In a paper just published in Nature, scientists collaborating on the GoAmazon study describe how they tracked particles in the largely pristine atmosphere over the Amazon rainforest, which has given them a way to effectively turn back the clock a few hundred years.
The scientists, sponsored in part by the U.S. Department of Energy’s (DOE) Atmospheric Radiation Measurement (ARM) Climate Research Facility and DOE’s Atmospheric System Research (ASR) Program, collected and analyzed data over the Amazon during 2014-15. By scanning the skies at different altitudes and measuring the changes in particle population over time, the scientists figured out the source of the tiny particles that trigger cloud formation under “pre-industrial” conditions.
The analysis described in the Nature paper, led by scientists from DOE’s Brookhaven National Laboratory, reveals that in the skies above the Amazon, large numbers of small aerosol particles that form naturally in the upper atmosphere are carried to the lower atmosphere, known as the “boundary layer,” by rapid downdrafts associated with rainfall. Then, in the boundary layer, where volatile organic compounds emitted by trees react with oxidants, the oxidation products condense on these small particles and make them grow into the “nuclei” around which clouds form.
“In many other places we know that these cloud-forming particles are coming directly from emissions from cars and factories, or formed as industrial gas molecules condense to form new particles,” said Brookhaven Lab atmospheric chemist Jian Wang, one of the leaders of the study. “But in the Amazon, there are clean conditions—no cars, no factories—which means we can study this pristine environment to see what Earth was like before the industrial era in order to quantify what the change is. Our measurements will improve how these key atmospheric processes are represented in climate models.”
