By sampling clouds -- and making their own -- researchers have shown for the first time a direct relation between lead in the sky and the formation of ice crystals that foster clouds. The results suggest that lead generated by human activities causes clouds to form at warmer temperatures and with less water. This could alter the pattern of both rain and snow in a warmer world.
The lead-laden clouds come with a silver lining, however. Under some conditions, these clouds let more of the earth's heat waft back into space, cooling the world slightly. Atmospheric lead primarily comes from human sources such as coal.
The international team of researchers reported their results in the May issue of Nature Geoscience. The collaboration included researchers from institutions in the United States, Switzerland and Germany.
"We know that the vast majority of lead in the atmosphere comes from man-made sources," said atmospheric chemist Dan Cziczo of the Department of Energy's Pacific Northwest National Laboratory and study author. "And now we show that the lead is changing the properties of clouds and therefore the balance of the sun's energy that affects our atmosphere."
Globe Trotting for Lead
Scientists first attempted to goad rain from the sky with silver and lead iodide in the 1940s. Since then, researchers have known that lead can pump up the ice crystals in clouds. But daily human activities also add lead to the atmosphere. The top sources include coal burning, small airplanes flying at the altitude where clouds form, and construction or wind freeing lead from the ground. Cziczo and colleagues wanted to know how lead from these sources affects clouds.
To find out, the researchers collected air from high atop a mountain peak on the Colorado-Wyoming border. In their high altitude lab, they created artificial clouds from the air in a cloud chamber about the size of a small refrigerator. Half of the ice crystals they plucked from the synthetic clouds, they found, contained lead.
The team then collected a dollop of real cloud atop a mountain in Switzerland. About half of those ice crystals also contained lead. But finding lead in an incriminating position doesn't mean it causes ice crystals.
To determine whether lead causes ice crystals and clouds to form, the team turned to a lab in Germany that houses a cloud chamber three stories tall, as well as a smaller chamber in Switzerland. They created dust particles that were either lead-free or contained one percent lead by weight, which is about what scientists find in the atmosphere. They put these dust particles into the chambers and measured the temperature and humidity at which point ice nucleated around the dust.
They found that lead changed the conditions under which clouds appeared. The air didn't have to be as cold or as heavy with water vapor if lead was present.
"Most of what nucleates clouds are dust particles," said Cziczo. "Half of the ones we looked at had lead supercharging them."
Leaden Clouds, Cooler Climes
To investigate what this might mean for the earth's climate, the researchers simulated the global climate with either lead-free dust particles floating around, or with either 10 percent or all of them containing lead.
The computer simulation showed that the clouds they looked at -- typically high, thin clouds -- formed at lower altitudes and different locations in the northern hemisphere when lead was present in dust particles. This will probably affect precipitation, said Cziczo.
"In our atmosphere, lead affects the distribution and density of the kinds of clouds we looked at," said Cziczo, "which might then affect where and when rain and snow fall."
Clouds at lower altitudes let more of the earth's heat, or so-called longwave radiation, escape out to space. So lead-triggered clouds could partly offset global warming due to greenhouse gases.
But that doesn't mean lead in the atmosphere will simply cool the planet, said Cziczo, since they looked at only one type of cloud. Cloudy skies are far more complicated than their wispy image lets on.
"This work highlights how complex these interactions between lead and water vapor and temperature are," said Cziczo. "They're not as simple as greenhouse gases."
Future work will look at the type of lead and how much is needed to affect clouds and precipitation, as well as the atmospheric distribution of the metal dust.
Reference: D. J. Cziczo, O. Stetzer, A. Worringen, M. Ebert, S. Weinbruch, M. Kamphus, S. J. Gallavardin, J. Curtius, S. Borrmann, K. D. Froyd, S. Mertes, O. Möhler and U. Lohmann, Inadvertent Climate Modification Due to Anthropogenic Lead, Nature Geoscience, May 2009, DOI 10.1038/NGEO499 (http://www.nature.com/ngeo/index.html).
This research was supported by the Atmospheric Composition Change the European Network for Excellence, ETH Zurich, the German Research Foundation, and Pacific Northwest National Laboratory directed research funding.
Pacific Northwest National Laboratory is a Department of Energy Office of Science national laboratory where interdisciplinary teams advance science and technology and deliver solutions to America's most intractable problems in energy, national security and the environment. PNNL employs 4,250 staff, has a $918 million annual budget, and has been managed by Ohio-based Battelle since the lab's inception in 1965. Follow PNNL on Facebook, LinkedIn and Twitter.
A close-up look at an uncommon underwater eruption
11.01.2018 | Woods Hole Oceanographic Institution
Environmental history told by sludge: Global warming lets the dead zones in the Black Sea grow
10.01.2018 | Leibniz-Institut für Ostseeforschung Warnemünde
What enables electrons to be transferred swiftly, for example during photosynthesis? An interdisciplinary team of researchers has worked out the details of how...
For the first time, scientists have precisely measured the effective electrical charge of a single molecule in solution. This fundamental insight of an SNSF Professor could also pave the way for future medical diagnostics.
Electrical charge is one of the key properties that allows molecules to interact. Life itself depends on this phenomenon: many biological processes involve...
At the JEC World Composite Show in Paris in March 2018, the Fraunhofer Institute for Laser Technology ILT will be focusing on the latest trends and innovations in laser machining of composites. Among other things, researchers at the booth shared with the Aachen Center for Integrative Lightweight Production (AZL) will demonstrate how lasers can be used for joining, structuring, cutting and drilling composite materials.
No other industry has attracted as much public attention to composite materials as the automotive industry, which along with the aerospace industry is a driver...
Scientists at Tokyo Institute of Technology (Tokyo Tech) and Tohoku University have developed high-quality GFO epitaxial films and systematically investigated their ferroelectric and ferromagnetic properties. They also demonstrated the room-temperature magnetocapacitance effects of these GFO thin films.
Multiferroic materials show magnetically driven ferroelectricity. They are attracting increasing attention because of their fascinating properties such as...
The oceans are the largest global heat reservoir. As a result of man-made global warming, the temperature in the global climate system increases; around 90% of...
08.01.2018 | Event News
11.12.2017 | Event News
08.12.2017 | Event News
16.01.2018 | Materials Sciences
16.01.2018 | Materials Sciences
16.01.2018 | Power and Electrical Engineering