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
Saunders RW
(2012)
Insights into the photochemical transformation of iodine in aqueous systems: humic acid photosensitized reduction of iodate.
in Environmental science & technology
Saunders R
(2010)
An aerosol chamber investigation of the heterogeneous ice nucleating potential of refractory nanoparticles
in Atmospheric Chemistry and Physics
Saunders R
(2007)
Potential climatic effects of meteoric smoke in the Earth's paleo-atmosphere
in Geophysical Research Letters
Saunders R
(2010)
The formation and growth of Fe2O3 nanoparticles from the photo-oxidation of iron pentacarbonyl
in Journal of Aerosol Science
Saunders R
(2010)
Studies of the Formation and Growth of Aerosol from Molecular Iodine Precursor
in Zeitschrift für Physikalische Chemie
Saunders R
(2011)
A photo-chemical method for the production of olivine nanoparticles as cosmic dust analogues
in Icarus
Saunders R
(2012)
Interactions of meteoric smoke particles with sulphuric acid in the Earth's stratosphere
in Atmospheric Chemistry and Physics
Plane J
(2011)
On the role of metal silicate molecules as ice nuclei
in Journal of Atmospheric and Solar-Terrestrial Physics
Murray B
(2012)
Glass formation and unusual hygroscopic growth of iodic acid solution droplets with relevance for iodine mediated particle formation in the marine boundary layer
in Atmospheric Chemistry and Physics
Mahajan A
(2009)
High bromine oxide concentrations in the semi-polluted boundary layer
in Atmospheric Environment
Mahajan A
(2011)
DOAS observations of formaldehyde and its impact on the HOx balance in the tropical Atlantic marine boundary layer
in Journal of Atmospheric Chemistry
Mahajan A
(2010)
Measurement and modelling of tropospheric reactive halogen species over the tropical Atlantic Ocean
in Atmospheric Chemistry and Physics
MacDonald S
(2012)
DOAS measurements of formaldehyde and glyoxal above a south-east Asian tropical rainforest
in Atmospheric Chemistry and Physics
Kumar R
(2010)
Physical properties of iodate solutions and the deliquescence of crystalline I<sub>2</sub>O<sub>5</sub> and HIO<sub>3</sub>
in Atmospheric Chemistry and Physics
Kaltsoyannis N
(2008)
Quantum chemical calculations on a selection of iodine-containing species (IO, OIO, INO3, (IO)2, I2O3, I2O4 and I2O5) of importance in the atmosphere.
in Physical chemistry chemical physics : PCCP
Gómez Martín JC
(2013)
On the mechanism of iodine oxide particle formation.
in Physical chemistry chemical physics : PCCP
Gómez Martín JC
(2009)
Kinetic studies of atmospherically relevant silicon chemistry part I: silicon atom reactions.
in Physical chemistry chemical physics : PCCP
Gómez Martín JC
(2011)
Kinetic studies of atmospherically relevant silicon chemistry. Part III: Reactions of Si+ and SiO+ with O3, and Si+ with O2.
in Physical chemistry chemical physics : PCCP
Gómez Martín JC
(2009)
Kinetic studies of atmospherically relevant silicon chemistry. Part II: silicon monoxide reactions.
in Physical chemistry chemical physics : PCCP
Gómez Martín J
(2009)
Determination of the O-IO bond dissociation energy by photofragment excitation spectroscopy
in Chemical Physics Letters
Gómez Martín J
(2009)
Photochemistry of OIO: Laboratory study and atmospheric implications
in Geophysical Research Letters
Dhomse S
(2014)
Aerosol microphysics simulations of the Mt.~Pinatubo eruption with the UM-UKCA composition-climate model
in Atmospheric Chemistry and Physics
Dhomse S
(2013)
Plutonium-238 observations as a test of modeled transport and surface deposition of meteoric smoke particles
in Geophysical Research Letters
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 | Belgium |
Start | 03/2012 |
End | 03/2017 |
Description | Leverhulme Trust |
Amount | £177,000 (GBP) |
Funding ID | F/00 122/BB |
Organisation | The Leverhulme Trust |
Sector | Charity/Non Profit |
Country | United Kingdom |
Start | 05/2011 |
End | 06/2014 |