Early white paper draft version- October 2013
This preliminary draft is intended as a consultation document.
Comments/edits welcome. Please do not use or cite.
Theme 5: Ocean emissions and tropospheric oxidizing capacity
Co-authors: Roland von Glasow and Eric Saltzman
1. Brief statement defining the theme:
Compounds that can affect the tropospheric oxidation power are being exchanged across the air-sea interface.
This includes reactive (inorganic) halogens, sulphur-containing compounds, halocarbons with lifetimes of
minutes to weeks, halogen-containing aerosol particles, certain organic gases, nitrogen-containing gases as well
as organic aerosol.
2. The scientific and societal basis justifying research on this issue. Why is it critical and why does it
need to be done now? What is the end goal? Why is international coordination required?
The oxidation capacity of the troposphere is key for the self-cleansing capability of the troposphere and is to a
large degree determined by ozone, which also acts as a greenhouse in the troposphere. Methane is a very
strong greenhouse gas, which is predominantly broken down in the marine troposphere, especially in the tropics.
These two gases are the only greenhouse gases that have relevant chemical sinks in the troposphere.
Air quality and climate change are some of the most important challenges that our societies face but despite
decades of research large uncertainties remain to quantify the response of the Earth’s climate system to natural
and anthropogenic emissions. Pollution and issues relating to the oxidation capacity of the atmosphere are
global issues due to atmospheric transport patterns and lifetimes of these compounds in the atmosphere. In
brief, these challenges are global challenges and can efficiently only be addressed in the international
framework
3. Background – major scientific concepts, key prior work defining the issues:
In the last decades the importance of natural emissions from the oceans on the composition and reactivity of the
troposphere has been established and major progress has been made. The quantification of the bidirectional
fluxes is however still very uncertain and recent discoveries of new interactions show that our knowledge about
ocean-atmosphere interactions is still limited.
The compounds exchanged at the ocean-atmosphere interface can be divided into the following groups:
 Inorganic halogens (e.g., I2, HOI)
 Organic halogens (e.g., CH3I, CH2I2, CHBr3...)
 Sulphur-containing compounds (e.g., dimethylsulphide, DMS)
 Volatile organic compounds (VOCs) and oxidized volatile organic compounds (OVOCs) (e.g., isoprene,
methanol, acetone)
 Nitrogen-containing gases (e.g., ammonia, amines, alkyl nitrates)
 Primary marine aerosol (organic and inorganic)
The marine troposphere is furthermore exposed to long-range transport from the continents, especially coastal
cities and emissions from ships.
Inorganic halogens can be directly released from the ocean surface (e.g., I2, HOI, Carpenter et al., 2013),
originate from the breakdown of organic halogens or be released by acid displacement or photochemical
reactions from sea salt aerosol. Inorganic halogens destroy ozone very efficiently but also oxidise DMS, the
greenhouse gas CH4 (only Cl atoms) and iodine oxides can lead to particle formation and growth (e.g., SaizLopez et al., 2012). Recent studies showed that reactive halogens can account for about a third of
photochemical ozone destruction in the North Atlantic (e.g., Read et al., 2008, Sommariva and von Glasow,
2012) and likely also in other ocean regions. Global model studies suggest an important role of halogens, mainly
of marine origin, for the ozone budget in the free troposphere as well (see e.g. Saiz-Lopez and von Glasow,
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2012, for a recent review on tropospheric halogen chemistry).
Most of the photochemical loss of the greenhouse gas methane occurs in the marine troposphere by reaction
with the OH radical. Measurements in the North Atlantic further suggested that up to 15% of the breakdown of
methane could be due to chlorine chemistry (Lawler et al., 2011).
Figure: Simplified schematic depiction of the most important halogen-related processes in the troposphere.
(From Saiz-Lopez and von Glasow, 2012)
Ozone concentrations are further affected by long-range transport and ship emissions but potentially also by NO x
released from marine alkyl nitrates.
Dimethylsulphide is produced biologically in the ocean and together with volcanic emissions amounts for the
bulk of natural sulphur emissions. The resulting SO2 and is a precursor for sulphate aerosol and plays a role in
the formation and growth of aerosol particles and can lead to the formation/growth of so-called cloud
condensation nuclei (CCN). Aerosol particles (sea salt, sulphate, organic) play an important role as CCN and
can affect climate directly by scattering sunlight.
The detection of the very shortlived glyoxal (Sinreich et al., 2010) over the eastern Pacific Ocean might indicate
that large, currently unquantified sources exist. A large number of Volatile organic compounds (VOCs) and
oxidized volatile organic compounds (OVOCs) are monitored on the Cape Verde site (Carpenter et al., 2010)
and their importance for regional and global ozone production needs to be established.
4. Approaches – what will it take to make substantive progress on the issue? What will be achieved in
the 10 years of Future SOLAS?
In order to make substantive progress in this field a combination of smaller “pilot” field studies combined with
larger campaigns that are ship and / or aircraft based are required. These should be supported by model studies
to support the field campaigns but also to improve our process understanding and to upscale from the study
region to ocean basins and globally.
Many fundamental questions regarding reaction pathways especially related to multiphase reactions are still
unknown hence laboratory studies that address these issues are essential.
Measurements over the oceans always require coordination between various groups in terms of logistics but
also regarding the scientific equipment as a full characterisation of the composition of the atmosphere (gas
phase and aerosol) is usually beyond individual laboratories and often requires scientists from different
countries.
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5. Community readiness – is there an existing community engaged on this issue? Are there institutional
or other barriers to progress? Is infrastructure or human capacity building required in order to achieve
the goals?
SOLAS has made a major contribution to the establishment of an international community and the training of the
next generation of scientists through its open science meetings, focussed workshops and summer schools. This
is a great achievement but an ongoing effort is required to maintain the links in this “new” community.
6. External connections – what partnerships are required in order to achieve the goals? What
mechanisms will be used to accomplish the interactions?
The issues related to atmospheric composition have a strong connection with the International Global
Atmospheric Chemistry (IGAC) project as well as the international Commission on Air Chemistry and Global
Pollution (iCACGP).
Focussed workshops have been held for specific topics partly together with IGAC. The SOLAS/IGAC sponsored
task Halogens in the Troposphere has also played a role in this.
Coordination of these collaborations is essential to enable progress in this important field. Funding through the
Belmont Forum would facilitate international collaboration and lobbying to this end would be very helpful.
7. Sustainability – articulate relationship (if any) between this project and the FE goals of Global
Development and Transformation Towards Sustainability.
The oceans provide a vast amount of ecosystem services to humanity. Pollution of the atmosphere has a
detrimental effect on this. Furthermore it is likely that the processes listed above are affected by Global Change
but given the link with greenhouse gases Global Change is also affected by oxidative processes or marine gases
and particles in the troposphere.
References:
Carpenter et al., Seasonal characteristics of tropical marine boundary layer air measured at the Cape Verde
Atmospheric Observatory, J. Atmos. Chem, 2010, 67, 87 - 140
Carpenter , L. J. and S. M. MacDonald and M. D. Shaw and R. Kumar and R. W. Saunders and R. Parthipan
and J. Wilson and J. M. C. Plane, Atmospheric iodine levels influenced by sea surface emissions of inorganic
iodine, Nature Geosc., 2013, 6, 108 - 111
Lawler, M. J., R. Sander, L. J. Carpenter, J. D. Lee, R. von Glasow, R. Sommariva, and E. S. Saltzman
HOCl and Cl2 observations in marine air, Atmos. Chem. Phys., 11, 7617-7628, 2011
Read et al., Extensive halogen-mediated ozone destruction over the tropical Atlantic Ocean, Nature, 2008, 453,
1232 - 1235
Saiz-Lopez A. and R. von Glasow, 2012, Reactive halogen chemistry in the troposphere. Chem. Soc. Rev.,
2012, 41, 6448-6472, DOI:10.1039/C2CS35208G
Saiz-Lopez, A., J. M. C. Plane, A. R. Baker, L. J. Carpenter, R. von Glasow, J. C. Gomez Martin, G. McFiggans
and R. W. Saunders, Atmospheric Chemistry of Iodine, Chem. Rev., 112, 1773-1804, 2012
Sinreich, R., S. Coburn, B. Dix and R. Volkamer, Ship-based detection of glyoxal over the remote tropical Pacific
Ocean, Atmos. Chem. Phys., 2010, 10, 11359 – 11371
Sommariva, R. and R. von Glasow, Multi-phase halogen chemistry in the tropical Atlantic Ocean, Env. Sci.
Tech., 46, 10429-10437, 2012
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