MSGID: 1:317/3 6430ede2   
   PID: hpt/lnx 1.9.0-cur 2019-01-08   
   TID: hpt/lnx 1.9.0-cur 2019-01-08   
    Scientists discover a way Earth's atmosphere cleans itself    
    Chemist helped shed light on the formation of an air-clearing molecule   
      
      
     Date:   
         April 7, 2023   
     Source:   
         University of California - Irvine   
     Summary:   
         Human activities emit many kinds of pollutants into the air, and   
         without a molecule called hydroxide (OH), many of these pollutants   
         would keep aggregating in the atmosphere.   
      
      
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   FULL STORY   
   ==========================================================================   
   Human activities emit many kinds of pollutants into the air, and without   
   a molecule called hydroxide (OH), many of these pollutants would keep   
   aggregating in the atmosphere.   
      
      
   ==========================================================================   
   How OH itself forms in the atmosphere was viewed as a complete story,   
   but in new research published in Proceedings of the National Academy of   
   Sciences, a research team that includes Sergey Nizkorodov, a University of   
   California, Irvine professor of chemistry, report that a strong electric   
   field that exists at the surface between airborne water droplets and   
   the surrounding air can create OH by a previously unknown mechanism.   
      
   It's a finding that stands to reshape how scientists understand how   
   the air clears itself of things like human-emitted pollutants and   
   greenhouse gases, which OH can react with and eliminate. "You need OH   
   to oxidize hydrocarbons, otherwise they would build up in the atmosphere   
   indefinitely," said Nizkorodov.   
      
   "OH is a key player in the story of atmospheric chemistry. It initiates   
   the reactions that break down airborne pollutants and helps to remove   
   noxious chemicals such as sulfur dioxide and nitric oxide, which   
   are poisonous gases, from the atmosphere," said Christian George, an   
   atmospheric chemist at the University of Lyon in France and lead author   
   of the new study. "Thus, having a full understanding of its sources and   
   sinks is key to understanding and mitigating air pollution."  Before,   
   researchers assumed that sunlight was the chief driver of OH formation.   
      
   "The conventional wisdom is that you have to make OH by photochemistry or   
   redox chemistry. You have to have sunlight or metals acting as catalysts,"   
   Nizkorodov said. "What this paper says in essence is you don't need any   
   of this. In the pure water itself, OH can be created spontaneously by   
   the special conditions on the surface of the droplets."  The team built   
   on research from Stanford University scientists led by Richard Zare that   
   reported spontaneous formation of hydrogen peroxide on the surfaces of   
   water droplets. The new findings help interpret the unexpected results   
   from the Zare group.   
      
   The team measured OH concentrations in different vials -- some containing   
   an air-water surface and others containing only water without any air --   
   and tracked OH production in darkness by including a "probe" molecule   
   in the vials that fluoresces when it reacts with OH.   
      
   What they saw is that OH production rates in darkness mirror those and   
   even exceed rates from drivers like sunlight exposure. "Enough of OH will   
   be created to compete with other known OH sources," said Nizkorodov. "At   
   night, when there is no photochemistry, OH is still produced and it is   
   produced at a higher rate than would otherwise happen."  The findings,   
   Nizkorodov reported, alter understanding of the sources of OH, something   
   that will change how other researchers build computer models that attempt   
   to forecast how air pollution happens.   
      
   "It could change air pollution models quite significantly," Nizkorodov   
   said.   
      
   "OH is an important oxidant inside water droplets and the main assumption   
   in the models is that OH comes from the air, it's not produced in   
   the droplet directly."  To determine whether this new OH production   
   mechanism plays a role, Nizkorodov thinks the next step is to perform   
   carefully designed experiments in the real atmosphere in different parts   
   of the world.   
      
   But first, the team expects the results to make a splash in the   
   atmospheric research community.   
      
   "A lot of people will read this but will not initially believe it and will   
   either try to reproduce it or try to do experiments to prove it wrong,"   
   said Nizkorodov. "There will be many lab experiments following up on   
   this for sure."  He added that UCI is a prime place for such science to   
   continue happening, because other labs at UCI, like that of Ann Marie   
   Carlton, professor of chemistry, focus their efforts on the role water   
   droplets play in the atmosphere.   
      
   This project, which was funded by the European Research Council, involved   
   researchers from France's University Claude Bernard, China's Guangdong   
   University of Technology, and Israel's Weizmann Institute.   
      
       * RELATED_TOPICS   
             o Earth_&_Climate   
                   # Air_Quality # Pollution # Air_Pollution #   
                   Environmental_Science # Environmental_Issues # Atmosphere   
                   # Water # Environmental_Awareness   
       * RELATED_TERMS   
             o Atmospheric_dispersion_modeling o Meteorite o Air_pollution   
             o Water_resources o Water_pollution o Pollution o   
             Planetary_boundary_layer o Ionosphere   
      
   ==========================================================================   
   Story Source: Materials provided by   
   University_of_California_-_Irvine. Note: Content may be edited for style   
   and length.   
      
      
   ==========================================================================   
   Journal Reference:   
      1. Kangwei Li, Yunlong Guo, Sergey A. Nizkorodov, Yinon Rudich, Maria   
         Angelaki, Xinke Wang, Taicheng An, Sebastien Perrier, Christian   
         George.   
      
         Spontaneous dark formation of OH radicals at the interface of   
         aqueous atmospheric droplets. Proceedings of the National Academy   
         of Sciences, 2023; 120 (15) DOI: 10.1073/pnas.2220228120   
   ==========================================================================   
      
   Link to news story:   
   https://www.sciencedaily.com/releases/2023/04/230407133443.htm   
      
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