Isoprene oxidation and OH recycling

Lead Research Organisation: University of Bristol
Department Name: Chemistry


The surface temperature of the Earth varies dramatically from polar regions through to equatorial ones. There are many factors that give rise to this temperature variation but the main ones are; the amount of heat energy arriving at the surface from the sun (which is smaller at the poles than the equator), the reflectivity of the Earth (called the albedo) which determines how much of the sun's energy is simply reflected back to space (and includes clouds and ice at the surface) which cool the surface and the amount of greenhouse gases in the atmosphere which act as a blanket around the Earth (preventing heat from the Earth from escaping to space) and warm the surface up.

Plants play a vital role in the Earth system, converting carbon dioxide and water into sugars and oxygen (essential for life) during photosynthesis. They also absorb a range of pollutants on their surfaces and are planted in urban areas in part to reduce the levels of particulate matter. However, plants also release a cocktail of chemicals for a variety of reasons, e.g. attracting pollinators, defence against predators and protection against a variety of pollutants such as ozone. The hydroxyl radical (OH) is a species produced in the atmosphere that acts like a chemical detergent, mopping up pollutants and cleansing the atmosphere. It was believed that these chemicals released by plants suppressed the hydroxyl radical and therefore would increase the level of greenhouse gases. However, recent measurements of the level of OH in the tropics suggest that this idea is wrong and that these chemicals actually lead to OH recycling.

If this is correct then plants and in particular those in tropical regions, will be playing a significant role in off-setting climate change. If the recycling of OH is correct then these plant emissions are leading to a reduction in the amount of greenhouse gases present in the atmosphere.
In addition, it is believed that these emissions may also lead to aerosol species that will help to form cloud and further cool the planet. Therefore, this combination of effects could be extremely important to our understanding of the Earth's climate (past, present and future). It will also of course have important implications for forest ecosystems, the enhanced negative impact of deforestation in tropical regions and land-use strategies in general.

A variety of scientists have speculated about how these chemicals may be leading to a recycling of OH, some based on laboratory experiments. However, the ones that appear to have the biggest potential impact and may resolve, at least in part, the discrepancy between measurements and computer simulations, are based on computer based calculations themselves. Therefore, it is vital that these theoretical studies be verified in the laboratory. These reactions are difficult to study and so we propose to add tags (swapping hydrogen for deuterium)to some of the chemicals we wish to study so that we can follow the reaction pathway more easily. We will use a range of detectors in concert with both a flow system and a static reaction chamber. Both systems will allow us to stufy different aspects of the chemical system. The detectors we will use include mass spectrometry (where we identify compounds by their weight) and spectroscopy (where we identify compounds by the amount of a specific colour of light that they absorb). These instruments have been developed at the two Universities involved (Bristol and Manchester) and allow them to be uniquely placed to be one of the few teams in the world able to carry out these studies.

Planned Impact

The laboratory based kinetic and mechanistic data collected in this proposal on the degradation pathways for the low NOx, OH initiated oxidation of isoprene (after suitable quality control and analysis) will be made available to all users via the websites of both the Manchester and Bristol groups. In addition these data will be described and analysed in a series of research papers that will be submitted to Journals such as Atmospheric Chemistry and Physics, Journal of Geophysical Research and Environmental Science and Technology.

These data will also be used to develop a modified mechanism for low NOx oxidation of isoprene based on both the Master Chemical Mechanism and the Common Representative Intermediates methodologies. These mechanisms will also be available from the groups' websites but also from the main MCM website as well for anyone to use. The MCM (containing the CRI) website provides users with the opportunity to download the mechanism is a variety of different formats, suitable to the users needs. These modified mechanisms will be used in both a regional (trajectory model) and the global model CRI-STOCHEM. The models will be intergrated and compared with available field data to assesses the impact on OH recycling. The results from these integrations will also form the basis for a research paper.

We will attend UK (e.g. university departmental seminar series, Royal Society of Chemistry's Gas-Kinetics meetings, Royal Meteorological Societies Atmospheric Chemistry Group meetings and the R. Met. Soc. annual conference) and international meetings (e.g. EGU and AGU) to present this work in both oral presentations and poster form.

Between the two groups we have active collaborations with a number of UK research groups and Centres (e.g. NERC National Centre for Atmos. Sci., NERC Centre for Ecology and Hydrology) as well as many groups outside the UK. In the course of these collaborations we would give presentations on visits, discuss new data via e-mail etc. and receive feedback.

We already have regular contact with the U.K. Met. Office and DECC (Dept. Energy and Climate Change) through other on-going projects and will update them on progress of this work. Other groups we interact with include, the UK Home Office, DSTL (Porton Down), a range of instrument manufacturers and chemical suppliers and as a matter of course we update them about new work we are undertaking.

We will write a layman's summary of the outcomes of the project and this will be posted on our websites too. In addition we will develop about 3 pages that will be based on Bristol ChemLabS' very successful Dynamic Laboratory Manual. The dynamic web-pages will be directed at a general audience (suitable for average 10 year olds for the basic one and 14 year olds and then 16 year olds for the other two) and will cover the background to atmospheric pollution and climate change.

Through the help of the Bristol ChemLabS' School Teacher Fellow and Science Communicator in Residence, Tim Harrison, this project will give talks heavily populated with lively experiments, called a 'Pollutants' Tale' for secondary school and older (> 11 years old) and 'Gases in the air' for primary school (4-11 years old), at schools, UK science festivals and to general interest groups. We expect to engage with at least 15,000 people directly by the end of this three year project. We will also write at least one article for the journal Science in School, which is read by 130,000 schools, their teachers and students across Europe. Articles we have written on atmospheric chemistry in the past 3-4 years have been downloaded over 250,000 times. These papers have also led to us providing a book chapter of a work on the Earth's Climate.

Our strategy for impact covers; academics and research centres through talks, papers and personal contact; other interested bodies through meetings and layman's reports; schools and the wider public through articles and talks.


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Khan M (2015) Global modeling of the C1-C3 alkyl nitrates using STOCHEM-CRI in Atmospheric Environment

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Khan M (2020) Global and regional model simulations of atmospheric ammonia in Atmospheric Research

Description The oxidation of isoprene is very important and through laboratory and modelling studies we have shown that it has a global impact through enhancement of OH levels. Such enhancements reduce greenhouse lifetimes (e.g. CH4)
Exploitation Route We are working with the MCM team at Leeds to make sure that our data are incorporated into the latest version of the mechanism so that it can be used by others in the community
Sectors Education,Environment,Transport

Description We have provided data for schools to use as examples of environmental data. We have supported schools projects with this work, e.g. walk to school projects
First Year Of Impact 2014
Sector Education
Description Leverhulme Grant Scheme
Amount £186,000 (GBP)
Organisation The Leverhulme Trust 
Sector Charity/Non Profit
Country United Kingdom
Start 02/2014 
End 02/2017
Description Please look at this details the myriad outreach work that we do 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Schools
Results and Impact We run numerous Outreach activities please refer to the website log.

Please read our education papers
1. Criegee Biradicals and Climate Change. D.E. Shallcross and T.G. Harrison. Education in Chemistry 50(5) 22-24, 2013
2. Creating Climate Change Awareness in South African Schools Through Practical Chemistry Demonstrations. Suthananda N Sunassee, Ryan M Young, Joyce D Sewry, Timothy G Harrison, Dudley E Shallcross. Acta Didactica Napocensia 4, 35-48 (2012).
3. Outreach within the Bristol ChemLabS CETL (Centre for Excellence in Teaching and Learning). D.E. Shallcross, T.G. Harrison, T.M. Obey, S.J. Croker, N.C. Norman. Higher Education Studies 3(1), 39-49, 2013
Year(s) Of Engagement Activity Pre-2006,2006,2007,2008,2009,2010,2011,2012,2013,2014