New particles in the atmosphere: two non-classical examples

Lead Research Organisation: University of Leeds
Department Name: Sch of Chemistry

Abstract

Small particles play several very important roles in the atmosphere. They provide surfaces on which exotic chemical reactions can take place, and they act as the condensation nuclei ('seeds') on which water condenses to form ice particles and cloud droplets. Particles may also reflect visible and UV sunlight back to space (cooling the earth), and absorb outgoing infra-red radiation (contributing to the 'greenhouse' effect). For thermodynamic reasons (decreasing entropy), it is actually quite difficult to form new particles in the atmosphere from gaseous constituents. This process is known as homogeneous nucleation: a few molecules condense together to form a stable cluster (about 1 nm in size), which then becomes the building block for further growth. This proposal will examine two examples of homogeneous nucleation that occur in very different regions of the atmosphere: iodine oxide particles, which form in the marine boundary layer from iodine species that are produced biogenically in the ocean; and meteoric smoke particles, which form in the middle atmosphere from the metals and silicon oxides that ablate from meteoroids. For both these systems, we want to follow the evolution of the particles from single molecules to particles containing about 1 million molecules (diameter about 50 nm), in order to understand what controls the rate of growth and the shapes of the particles. Preliminary work shows that the particles are fractal-like ('fluffy'), with large surface areas which often facilitate chemical reactions. For example, meteoric smoke particles may influence some of the chemistry controlling ozone in the stratosphere. We will also examine the properties of these particles as ice condensation nuclei. Iodine oxides have recently been observed at high concentrations over coastal Antarctica, and could be a source of ice nuclei near the surface. Meteoric smoke particles are most likely the nuclei for noctilucent clouds. These ice clouds, which form around 83 km at high latitudes during mid-summer, were first observed at the end of the 19th Century. This has led to speculation that they are an early indicator of climate change in the middle atmosphere. Finally, we will address the question of how meteoric smoke particles descend from around 80 km to the earth's surface. The particles have been detected both by capturing them with a rocket-borne instrument flying above 70 km (in this project we propose to analyze some of these captured particles), and by detecting cosmic iridium and platinum in ice cores from Greenland and Antarctica. We will use the Met Office's general circulation model to study the transport pathways during present-day conditions and during a glacial maximum, in order to interpret the ice core record over several hundred thousand years.

Publications

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Gómez Martín J (2009) Photochemistry of OIO: Laboratory study and atmospheric implications in Geophysical Research Letters

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Gómez Martín JC (2009) Kinetic studies of atmospherically relevant silicon chemistry. Part II: silicon monoxide reactions. in Physical chemistry chemical physics : PCCP

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Gómez Martín JC (2013) On the mechanism of iodine oxide particle formation. in Physical chemistry chemical physics : PCCP

 
Description Iodine oxide nano-particles form in the marine boundary layer when iodine species (both inorganic and organic) are emitted from the ocean. In this project we showed that polymerization of IO and OIO form the higher oxides which polymerize into particles extremely rapidly: that is, without any entropic barriers. These particles can then act as condensation nuclei.

Metal silicate particles form in the earth's mesosphere from the metallic vapours produced by meteoric ablation. Again we showed through laboratory kinetic measurements that these particles form spontaneously. The resulting particles, termed meteoric smoke particles, act as ice nuclei for Noctilucent (also termed Polar Mesospheric) clouds, which are almost certainly sensitive indicators of climate change in the upper atmosphere.
Exploitation Route The role of meteoric smoke particles as ice nuclei in the mesosphere can now be implemented in global chemistry-climate models. Similarly, the role of iodine oxides as condensation nuclei in the remote marine boundary is now being implemented in global models.
Sectors Aerospace, Defence and Marine,Environment

 
Description The results have been used by atmospheric scientists.
Sector Environment
Impact Types Cultural

 
Description ERC Advanced Grant
Amount € 2,480,000 (EUR)
Funding ID 291332 CODITA 
Organisation European Research Council (ERC) 
Sector Public
Country European Union (EU)
Start 04/2012 
End 03/2017
 
Description Leverhulme Trust
Amount £177,000 (GBP)
Funding ID F/00 122/BB 
Organisation The Leverhulme Trust 
Sector Academic/University
Country United Kingdom
Start 06/2011 
End 06/2014