{"192601":{"#nid":"192601","#data":{"type":"news","title":"Pollution Doesn\u2019t Change the Rate of Cloud Droplet Formation, Study Shows","body":[{"value":"\u003Cp\u003EWhen it comes to forming the droplets that make up clouds, a little oily and viscous organic material apparently doesn\u2019t matter that much. And that\u2019s good news for reducing the uncertainty of climate model predictions.\u003C\/p\u003E\u003Cp\u003EUnderstanding cloud formation is essential for accurate climate modeling, and understanding cloud formation begins with the droplets that make up clouds. Droplets form when water vapor is attracted to particles floating in the atmosphere. These particles include dust, sea salt from the ocean, microorganisms, soot, sulfur \u2013 and organic material that can be both viscous and oily.\u003C\/p\u003E\u003Cp\u003EFor years, scientists had believed that particles coated with this organic \u201cgoop\u201d \u2013 produced by combusted petroleum and biomass \u2013 could form droplets more slowly than other particles. That would have had a significant impact on the formation of clouds.\u003C\/p\u003E\u003Cp\u003EBut a study being reported this week in the journal \u003Cem\u003EProceedings of the National Academy of Sciences\u003C\/em\u003E suggests that the long-held belief isn\u2019t true. Based on aerial and ground-based measurements of droplet formation from ten different areas of the northern hemisphere, researchers at the Georgia Institute of Technology report that organic coatings on particles don\u2019t seem to significantly affect the rate at which droplets form. The researchers studied a wide range of particles, including organic, hydrocarbon-rich particles from the 2010 Deepwater Horizon oil spill in the Gulf of Mexico.\u003C\/p\u003E\u003Cp\u003E\u201cIt turns out that it doesn\u2019t matter how much goop you have \u2013 or don\u2019t have \u2013 the droplets take the same time to form,\u201d said \u003Ca href=\u0022http:\/\/www.eas.gatech.edu\/people\/Athanasios_Nenes\u0022\u003EAthanasios Nenes\u003C\/a\u003E, a professor in the \u003Ca href=\u0022http:\/\/www.eas.gatech.edu\/\u0022\u003ESchool of Earth and Atmospheric Sciences\u003C\/a\u003E and the \u003Ca href=\u0022http:\/\/www.chbe.gatech.edu\/\u0022\u003ESchool of Chemical and Biomolecular Engineering\u003C\/a\u003E at Georgia Tech. \u201cEven in extreme environments like Deepwater Horizon, the rate of droplet formation on particles found over the spill doesn\u2019t differ from that of typical sea salt particles.\u201d\u003C\/p\u003E\u003Cp\u003EThe research was scheduled to be published in the early online edition of the journal during the week of February 18th. The research was supported by the National Science Foundation (NSF), NASA, the Department of Energy (DOE), the National Oceanic and Atmospheric Administration (NOAA) and the Office of Naval Research (ONR).\u003C\/p\u003E\u003Cp\u003EClouds can hold in heat emitted from the Earth\u2019s surface, contributing to climate warming. But they can also reflect incoming sunlight back to space, producing a climate cooling effect. Predicting how cloud cover will change in the future is therefore essential to good climate modeling.\u003C\/p\u003E\u003Cp\u003E\u201cThe reason we care about droplet formation rates is because the more slowly the droplets form, the more droplets you end up having in clouds,\u201d Nenes said. \u201cThis, in turn, affects cloud properties and their climate impacts. For many years, there was the perception that having a lot of oily organic compounds from pollution would make water uptake a lot slower and might make droplets take longer to form. If that were true, it would mean that the impact pollution could have on clouds and climate would be much larger than we thought.\u201d\u003C\/p\u003E\u003Cp\u003EAnd that created a large question mark in climate models.\u003C\/p\u003E\u003Cp\u003ETo address that issue, Nenes and his collaborators began a series of studies using a mini cloud formation chamber small enough to be operated aboard an aircraft. The chamber consists of a long metal tube that is heated at one end and cooled at the other. The walls of the chamber are kept moist, and air containing particles from outside the aircraft is flowed through. Droplets form on the particles when air in the chamber becomes cool enough that it can no longer retain the moisture. The droplets then exit the chamber where they can be studied.\u003C\/p\u003E\u003Cp\u003E\u201cWith the chamber, we essentially create a cloud in a tube,\u201d Nenes said. \u201cThe difference between the cloud in the tube and the cloud outside is that the tube allows us to precisely control the temperature and the amount of water vapor available. We know exactly what is going on with that cloud, and this allows for very accurate measurements of cloud formation.\u201d\u003C\/p\u003E\u003Cp\u003EBeginning in 2004, Nenes and his graduate students took the chamber along on ten missions operated by NASA, NSF, NOAA and ONR. They flew through the pristine air of the Arctic, smoke from forest fires in Canada, and polluted air masses over the United States. They also sampled polluted air over Mexico City, clean air over the forests of Finland, and dust-laden air over the Mediterranean. Though the particles flowing through the cloud chamber were different each time, the rate at which they formed droplets, the condensation coefficient, remained the same.\u003C\/p\u003E\u003Cp\u003E\u201cWe have literally hundreds of hours of data studying cloud formation from areas all over the globe,\u201d Nenes said. \u201cWe didn\u2019t see any changes in the droplet nucleation time scale.\u201d\u003C\/p\u003E\u003Cp\u003EIn future studies, Nenes would like to study particles from other areas of the world, especially Africa and China. He\u2019d also like to see what happens when the temperature of the air flowing through the cloud chamber is cold enough to form ice. There is some evidence that the kinetics of ice formation may be different in particles that are rich in \u201cgoop.\u201d\u003C\/p\u003E\u003Cp\u003EThe study of droplet formation provides one small step toward reducing the uncertainty in climate modeling.\u003C\/p\u003E\u003Cp\u003E\u201cThis is good for atmospheric and climate scientists, because some of the uncertainty of droplet formation and aerosol impacts goes away,\u201d Nenes added. \u201cWith careful measurements and global deployment of measuring instruments, you can actually resolve outstanding questions in cloud physics and help simplify the descriptions of clouds in climate models.\u201d\u003Cbr \/\u003E\u003Cbr \/\u003E\u003Cstrong\u003EResearch News\u003C\/strong\u003E\u003Cbr \/\u003E\u003Cstrong\u003EGeorgia Institute of Technology\u003C\/strong\u003E\u003Cbr \/\u003E\u003Cstrong\u003E177 North Avenue\u003C\/strong\u003E\u003Cbr \/\u003E\u003Cstrong\u003EAtlanta, Georgia\u0026nbsp; 30332-0181\u003C\/strong\u003E\u003C\/p\u003E\u003Cp\u003E\u003Cstrong\u003EMedia Relations Contact\u003C\/strong\u003E: John Toon (404-894-6986)(\u003Ca href=\u0022mailto:jtoon@gatech.edu\u0022\u003Ejtoon@gatech.edu\u003C\/a\u003E)\u003C\/p\u003E\u003Cp\u003E\u003Cstrong\u003EWriter\u003C\/strong\u003E: John Toon\u003C\/p\u003E\u003Cp\u003E\u0026nbsp;\u003C\/p\u003E","summary":null,"format":"limited_html"}],"field_subtitle":"","field_summary":[{"value":"\u003Cp\u003EWhen it comes to forming the droplets that make up clouds, a little oily and viscous organic material apparently doesn\u2019t matter that much. And that\u2019s good news for reducing the uncertainty of climate model predictions.\u003C\/p\u003E","format":"limited_html"}],"field_summary_sentence":[{"value":"The presence of oily organic materials on atmospheric particles doesn\u0027t slow the formation of droplets that form clouds."}],"uid":"27303","created_gmt":"2013-02-16 18:43:48","changed_gmt":"2016-10-08 03:13:37","author":"John Toon","boilerplate_text":"","field_publication":"","field_article_url":"","dateline":{"date":"2013-02-18T00:00:00-05:00","iso_date":"2013-02-18T00:00:00-05:00","tz":"America\/New_York"},"extras":[],"hg_media":{"192561":{"id":"192561","type":"image","title":"Cloud formation chamber","body":null,"created":"1449179879","gmt_created":"2015-12-03 21:57:59","changed":"1475894843","gmt_changed":"2016-10-08 02:47:23","alt":"Cloud formation 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