The Role of Short-lived Species in the Tropical Atmosphere

Lead Research Organisation: University of Cambridge
Department Name: Chemistry


The halogens are vital components in the chemistry of the atmosphere, influencing ozone concentrations in the stratosphere and the troposphere. Currently, the supply of very short-lived halocarbons (VSLH) to the stratosphere is a major uncertainty in the stratospheric bromine budget, with VSLH providing up to 20% of the total bromine loading. The future supply to the stratosphere will likely be affected by climate-related changes in the emissions of VSLH arising from increases in sea surface temperatures and convection. VSLH emissions can also play a large role in determining O3 concentrations as high BrO levels could lead to depletion of O3 in the boundary layer and free troposphere. A significantly improved understanding of the marine, chemical and climatic factors affecting VSLH emission and atmospheric concentration is required to predict their importance as climate changes in the coming decades. The tropics with its large area, regions of convective intensity and highly productive oceans is critical. High values of CHBr3, CH2Br2 and other VSLH have been observed in the tropical Pacific and Atlantic oceans, providing evidence for the importance of emission hotspots in otherwise pristine atmospheres. Measurements of atmospheric concentrations of VSLH in the Western Pacific will be made from 2008-2012 under a recently awarded NERC grant on which I am the Principal Investigator. These time series will form a unique record of VSLH in this region, as they are continuous and highly time-resolved. The collection and interpretation of the measurements provide an excellent opportunity to make real breakthroughs in our understanding of scientific issues including the role of halogens in the global oxidative capacity and the role of iodocarbons in the production of aerosols and clouds in the marine boundary layer in this region of the tropics. I will broaden my research interests in the measurement of VSLH to provide increased knowledge and understanding of how short-lived halocarbons and hydrocarbons influence the tropical troposphere and stratosphere. The new, continuous measurements will be interpreted together with other measurements, principally the less frequent but 20 year record collected at the Univ Calif Irvine. Joint interpretation of the halocarbon data with meteorological and local marine records will enable the influence of climatic features such as El Nino and the Madden Julian Oscillation to be understood. These analyses of existing and new data will be used to design model studies using the NCAS/Met Office UKCA model. Data analysis and interpretation will be extended to include measurements from existing stations (Mace Head, Cape Verde, Weyborne and those in the AGAGE and NOAA networks) and from tropical campaigns such as the PEM series and OP3. The measurement system developed here with robust, autonomous instruments operating at remote sites with minimal human intervention has great potential to be extended to include other instruments based on the same philosophy and I will extend the measurements made by developing and deploying other robust instrument packages for autonomous use. From an atmospheric perspective, the West Pacific will be fascinating over the coming decades. Emissions of VSLH and hydrocarbons are likely to change significantly as a result of changes to natural habitats and increased industrialisation. The chemical mix in this region, strongly affected as it is by the pristine air over the Pacific Ocean itself, will evolve in a currently unpredictable way, with emissions, chemistry, meteorology and oceanic conditions all likely to change significantly. Overall, I will establish a world-leading programme interpreting measurements to understand the role of halo- and hydrocarbons in this region and in the global atmosphere. Once developed, this interpretative expertise can be used to address a much broader range of atmospheric change issues.


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Ashfold M (2015) Rapid transport of East Asian pollution to the deep tropics in Atmospheric Chemistry and Physics

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Ashfold M (2012) Transport of short-lived species into the Tropical Tropopause Layer in Atmospheric Chemistry and Physics

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Ashfold M (2014) Estimates of tropical bromoform emissions using an inversion method in Atmospheric Chemistry and Physics

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Chipperfield MP (2017) Detecting recovery of the stratospheric ozone layer. in Nature

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Gostlow B (2010) <i>ยต</i>Dirac: an autonomous instrument for halocarbon measurements in Atmospheric Measurement Techniques

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Harris N (2017) Coordinated Airborne Studies in the Tropics (CAST) in Bulletin of the American Meteorological Society

Description The main findings are

1. Marine emissions of halocarbons in the SE Asian region are substantially less than previously thought. However there are some transport processes which could provide an efficient means of lofting pollution from SE Asia into the upper troposphere and lower stratosphere.

2.There is a good photochemical understanding of the inter-annual variations in Arctic ozone loss.

3. Development of a new approach to make high resolution estimates of methane emissions in the UK which is needed for comparison with the UK inventories and to monitor changes. The technique is particularly promising for estimating agricultural and landfill emissions.

4. A much improved understanding of trends in the vertical distribution of ozone and the uncertainties associated with those trends.
Exploitation Route Various aspects of this work have policy implications and it is important to make sure that these are transmitted into the policy arena. The main route for exploitation is through publication in peer-reviewed journals.

I was lead author on Chapter 5 "Scenarios/Options for Policymakers" in the 2014 WMO/UNEP Assessment.

Evidence was given to the Environment Committee at the European Parliament on the potential for climate change mitigation of measures to control non-CO2 climate agents.

Information was given to the Sunday Times in an interview for a major article on CFC replacements.

A press release on the largest ever Arctic ozone loss led to extensive coverage around the world.

This work on ozone depletion was recognised by the NERC International and Overall Impact Awards.
Sectors Electronics,Environment

Description This fellowship has enabled participation in the public policy debate underlying the Montreal Protocol. I gave evidence to the European Parliament on greenhouse gases. I was lead author of the chapter on Policy options in the current WMO/UNEP Scientific Assessment of Ozone Depletion. These activities were part of the process that led to new, stricter controls on hydrofluorocarbons (HFCs) (Kigali Amendment of the Montreal Protocol). This resulted in being awarded the NERC International Impact Award and the NERC Overall Impact Award in 2015. The fellowship also led to the body of work needed to become WCRP/SPARC co-chair.
First Year Of Impact 2017
Sector Environment,Other
Impact Types Policy & public services

Description Cambridge Retrofit POG
Geographic Reach Local/Municipal/Regional 
Policy Influence Type Participation in a guidance/advisory committee
Impact The Cambridge Retrofit programme links people from the public, private and academic sectors with a view to developing ways for retrofitting buildings with increased energy efficiency.
Description Evidence to European Parliament ENV Committee on "Reduction of non-CO2 Emissions"
Geographic Reach Multiple continents/international 
Policy Influence Type Contribution to a national consultation/review
Impact This contributed to a resolution passed by the European Parliament and, in 2013, to the introduction of EU legislation on Fluorinated Greenhouse Gases limiting future HFC usage. More recently, in a report published in January 2014, the European Commission drafted new legislation that proposed to reduce HFCs by 79% (relative to current levels), by 2030. The paper, entitled "Proposal for a Regulation of the European Parliament and the Council on Fluorinated Greenhouse Gases" cited the 2010 Assessment of the Montreal Protocol. In March 2014, The European Parliament passed this legislation after parliamentarians voted overwhelmingly in its favour (644 for, 19 against, 16 abstaining). The climate benefit of this measure should be substantially greater than the European Kyoto Protocol targets.
Description Lead author, "A Focus on Information and Options for Policymakers", UNEP/WMO Scientific Assessment of Ozone Depletion: 2015, in press
Geographic Reach Multiple continents/international 
Policy Influence Type Participation in a guidance/advisory committee
Impact Continued reduction in CFCs; control of HFCs under Montreal Protocol
Description Collaboration with ECMWF 
Organisation European Centre for Medium Range Weather Forecasting ECMWF
Country United Kingdom 
Sector Public 
PI Contribution ECMWF will be external partners to this project providing meteorological information for flight planning during the field campaign and being involved in studies of trace gases in strong convection.
Start Year 2012
Description Collaboration with NASA ATTREX 
Organisation National Aeronautics and Space Administration (NASA)
Department NASA Dryden Flight Research Centre
Country United States 
Sector Public 
PI Contribution We have worked closely with NASA ATTREX to lay good foundations for the joint aircraft campaign in Jan/Feb 2013. The activities have included the ATTREX PI attending the CAST kick-off meeting, joint attendence at a workshop to discuss the science and planning for the campaigns, and a visit to learn about the NASA Global Hawk operations and flight planning during the second phase of ATTREX. NERC have signed one Agreement with NASA covering all CAST-ATTREX activities and as a second specifically about the direct UK in the Global Hawk is close to signing.
Collaborator Contribution NASA provided the Global Hawk
Impact Good coordination of flights. Joint science team meeting held in Boulder, CO in October 2014.
Start Year 2012
Description Collaboration with NSF CONTRAST 
Organisation National Science Foundation (NSF)
Country United States 
Sector Public 
PI Contribution Measurements from the ground to 20 km were made from Guam in the West Pacific in Jan/Feb 2014 as part of a NERC/NASA/NSF three aircraft collaboration looking at the impact of convection on the tropical UTLS. The NERC BAe-146 made low level measurements. Ground-based and sonde measurements were made in Manus (PNG) in the same period.
Collaborator Contribution NSF supported the deployment of their HIAPER atmospheric research aircraft in the joint deployment in Guam with the NERC BAe-146 and the NASA Global Hawk.
Impact All flights performed with good coordination between campaigns. Science team meeting held in Boulder CO in October 2014
Start Year 2013
Description International partnership building 
Organisation University of Malaya
Country Malaysia 
Sector Academic/University 
PI Contribution Series of group and individual meetings between PIs and development of a collaborative strategy. Meetings held in Norwich (UEA), Cambridge, Kuala Lumpur, Bachok (Malaysia), and opportunistically in New Zealand and Australia, and involving the majority of PI institutes (UEA), University of Cambridge, University of Malaya (UM), the Commonwealth Scientific and Industrial Research Organisation (CSIRO, Australia), and the National Institute of Water and Atmospheric Research (NIWA, New Zealand), as well as verbal contact with the National Central University of Taiwan. There was also a site visit to the the new research facility at Bachok, and the Malaysian Meteorology Department (MMD) weather station/radiosonde launch facility at Kota Bharu, both central to this project, with staff from UEA, Cambridge, UM and MMD. Graduate students from Malaysia are attending courses run by NCAS on atmospheric science. The collaboration continues since my move to Cranfield and we are involved with UM, UKM and MMD in the NERC Newton Fund project looking at air quality in the greater Klang Valley
Collaborator Contribution The demonstration activity held in Bachok, Malaysia in Jan/Feb 2014 successfully showed that several state-of-the-art instruments could be run in camapign mode in conjunction with the suite of instruments being installed by the University of Malaya for long-term observations.
Impact The campaign took place successfully. A joint science meeting was held in Cambridge, UK in September 2014 and a publication policy was agreed.
Start Year 2008
Description Exhibit at Royal Society Summer Exhibition 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? Yes
Geographic Reach National
Primary Audience Public/other audiences
Results and Impact We hopefully enthised lots of people of all ages about atmospheric science. It left us absolutely knackered. Great experience.

Nothing direct.
Year(s) Of Engagement Activity 2014
Description Open day in Guam 
Form Of Engagement Activity Participation in an open day or visit at my research institution
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Public/other audiences
Results and Impact Many inhabitants of Guam visited the airport to see our two research aircraft and to see what we were doing, learn why and see how the planes and instruments worked. This open day was supplemented by work in the local media and in schools.

n/a - just generally increased interest
Year(s) Of Engagement Activity 2014