Summary of the impact

Research by Lisa Emberson has led to tighter controls on air pollutant precursor emissions of ozone (O₃) across Europe benefiting crop and forest productivity, and grassland species composition. Emberson's research led to new risk assessment methods, based on knowledge of atmospheric exchange processes and plant eco-physiology, which assess O₃ uptake and related damage using novel flux-based `Critical Levels'. These new methods are being used to optimise emission reduction policy by 26 parties (member states) who have signed and ratified the United Nations Economic Commission for Europe (UNECE) Gothenburg Protocol established under the Convention on Long Range Transboundary Air Pollution (LRTAP).

Underpinning research

By the early 1990s a large body of experimental data existed describing the adverse impact of O₃ on crops, forests and grassland ecosystems. In Europe, efforts were made to compile data from standardised experiments to develop concentration based exposure-response relationships. These were used to establish `Critical Levels' (CLs) providing a policy tool for use in the `effects based' approach adopted by the UNECE LRTAP to optimise emission control across the region. However, these concentration-based risk assessments were compromised in their policy use since they were not suitable for quantification of ecosystem damage and therefore could not be used to estimate the benefits of emission reduction methods. This was due to their only being able to provide an assessment of potential impacts since they did not incorporate modifying factors (dependent upon species traits and prevailing environmental conditions) considered to affect plants sensitivity to O₃.

Emberson's research centred on the development and application of a novel flux-based risk assessment method. This method applied knowledge of plant ecophysiological processes to estimate relative potential O₃ uptake or stomatal O₃ flux (O₃ uptake via the leaf pores) and showed that the geographical distribution of relative risk differed substantially when using flux vs. concentration based methods (Emberson et al., 2000). This flux-based method was parameterised for important European vegetation types forming the core of what was later to become known as the DO₃SE (Deposition of Ozone and Stomatal Exchange) model (Emberson et al., 2007). This York developed model is the single model upon which the flux modelling methods now used by the LRTAP Convention are based.

To enhance the practical application of this flux-based method Emberson worked with colleagues from the European Monitoring and Evaluation Programme (EMEP) in Norway who assess European air quality for the LRTAP Convention. These colleagues use a chemical transport model (CTM) to provide estimates of atmospheric O₃ concentration. Incorporation of equations based on standard micrometeorological theory into the DO₃SE model allowed estimates of the O₃ transfer from the CTM output height to the vegetated surface. The original leaf level stomatal O₃ flux model was also developed for an entire canopy adding non-stomatal O₃ deposition processes (Emberson et al., 2001). This allowed DO₃SE to provide the estimate of total O₃ deposition in the EMEP CTM integrating the assessment of O₃ loss to the vegetated surface layer as well as O₃ ecosystem damage. Evaluation against European observational data showed the model performed well for a range of vegetation types and climatic conditions (Tuovinen et al., 2004).

The DO₃SE stomatal flux model was used in collaboration with experimentalists from across Europe; to derive novel flux-response relationships for a number of crop (Pleijel et al. 2007); forest (Karlsson et al., 2004; Karlsson et al., 2007) and semi-natural grassland (Emberson et al., in prep) species. These flux-response relationships have been used to establish new flux-based CLs (Mills et al., 2011a); as such they provide tools to ensure ecosystem protection and allow cost-benefit analysis of emission reductions to improve food security, carbon sequestration and biodiversity.

The validity of the flux-based approach was tested through collaboration with colleagues who host one of the LRTAP Task Forces which assesses air quality damage to vegetation (Integrated Co-operative Programme on Vegetation). These colleagues collate observational and standardised experimental data describing O₃ effects on vegetation across Europe; comparisons of the concentration and flux-based methods clearly showed that flux provided a far more realistic indication of the geographical distribution of O₃ damage across Europe (Mills et al. 2011b).

This research has been conducted since 1999 at the Stockholm Environment Institute (SEI), part of the Environment Dept. of the University of York where Emberson was first employed as a research associate and is now the Centre Director of the SEI York centre; as well as a senior lecturer in the Environment Dept.

References to the research

Details of the impact

The UNECE LRTAP Convention oversees the assessment of scientific evidence that form the basis of their effects based approach to identifying air pollution emission control options across Europe; detailed in their `multi-pollutant, multi-effect Gothenburg Protocol on Acidification, Eutrophication and Ground Level O₃'. This Protocol has been the driving force for the establishment of European legislation (EU Directives) on air quality policy as well as global, European and national air quality targets. Emberson's research was instrumental in revising CLs for O₃ which have been used by the Gothenburg Protocol (Mills et al., 2011a). The revision of the Protocol was conducted in May 2012. The following outlines the different aspects of Emberson's research that led to the revision of these O₃ air quality guidelines hence changing European emission control policy.

Development of the UNECEs LRTAP Chemical Transfer Model (CTM).
Development of the new DO₃SE O₃ deposition model for use in the EMEP CTM (Emberson et al., 2000b) allowed the flux-based methods to be applied across Europe for risk assessment and policy formulation. Peer review of the DO₃SE deposition methodology at a UNECE ad hoc workshop hosted by Emberson and Ashmore (also a York staff member) in Harrogate, 2002 allowed DO₃SE to become part of the `Unified EMEP model', the official model of the LRTAP Convention for use in European modelling of emission control scenarios for O₃ (Simpson et al., 2003). This model provides input to the LRTAP Conventions Integrated Assessment Modelling effort that applies cost-benefit methods to identify emission reduction options to guide European air quality policy.

Development of UNECEs LRTAP critical levels (CLs) for air quality risk assessment
The series of LRTAP Convention endorsed scientific workshops concluded that flux-based risk assessments performed using DO₃SE offered an improved geographical representation of risk to the existing concentration based methods and should be recommended for adoption by the LRTAP Convention. This led to revisions of the LRTAP Conventions Mapping Manual which documents the procedures and parameters to be used by member states of the LRTAP Convention in calculating and mapping CLs of air pollutants. The revised chapter described the DO₃SE stomatal flux algorithm, procedures for applying this across Europe, and the associated CLs and flux-response relationships from which they are derived; Fig 1 provides a comparison of the exceedance of CLs estimated using both concentration- and flux-based methods. The use of the flux-based method increases the geographical extent-, but alters the magnitude-of risk of the forest area across Europe (with increases in risk in more Northerly locations and reductions in risk in Mediterranean regions).

Development of air quality policy: Revision of UNECE LRTAP Gothenburg Protocol
Emberson and colleagues research to develop new methodologies to assess vegetation damage from ground level O₃ resulted in formal adoption by the LRTAP Convention of new CLs to protect ecosystems into the revised Gothenburg Protocol in May 2012. The current 2012 revised protocol has been signed and ratified by 31 and 26 countries or regions respectively across Europe (as well as the United States of America) and acts to control emissions of pollutants that will result in dangerous atmospheric levels of a number of different air pollutants (including nitrogen oxides and volatile organic compounds that are the primary local and regional pre-cursors of ground level O₃). The protocol is legally binding and once implemented should ensure the exposure of vegetation to excessive O₃ levels will be 44% down on 1990 levels.

Emberson's research has also raised awareness of the damaging effects of O₃ to ecosystems globally. This led to O₃ impacts on agricultural productivity being considered in an assessment of cost-benefits in controlling short-lived climate pollutants by a recent WMO/UNEP Black Carbon and Ozone report; since publication of this work various national action plans have been developed to combat short-lived climate pollutants in countries across the world. This initiative is led by the Climate and Clean Air Coalition established by Hilary Clinton of the US Department of State. Research showing the significance of O₃ effects on staple crops in South Asia (e.g. Emberson et al., 2009) also led the Malé Declaration to include O₃ effects on crop productivity as a challenge to overcome through international negotiation to control and prevent air pollution in the seven south Asian Malé Declaration countries. Emberson's research has also helped identify the threat to ecosystems from the hemispheric transport of O₃ and its precursor pollutants highlighting the need for globally coordinated action to control precursor emissions as regions are increasingly unable to manage air quality through domestic emission reduction policies (Emberson & West, 2010).

Sources to corroborate the impact

UNECE Gothenburg Protocol
http://www.unece.org/env/lrtap/multi_h1.html [see `Consolidated text of the amended protocol' document; Part III Critical Levels of Ozone ; A. For the Parties with geographical scope of EMEP; Part 6. pp 20]

Mills, G., Pleijel, H., Braun, S., Büker, P., Bermejo, V., Danielsson, H., Emberson, L., Grünhage, L., González Fernández, I., Harmens, H., Hayes, F., Karlsson, P.E., Simpson, D., (2011a) New stomatal flux-based critical levels for ozone effects on vegetation Short communication

UNECE CLRTAP Mapping Manual
http://icpvegetation.ceh.ac.uk/manuals/mapping_manual.html
Chapter 3: Mapping Critical Levels for Vegetation

EMEP Unified model description

Unified EMEP model code version `rv3', released as open source under the GPL license v3 in February 2008 http://www.gnu.org/copyleft/gpl.html .
Simpson, D., Benedictow, Berge, H., Bergstrom, R., Emberson, L.D., Fagerli, H., Flechard, C.R., Hayman, G.D., Gauss, M., Jonson, J.E., Jenkin, M.E., Nyıri, A., Richter, C., Semeena, V.S., Tsyro, S., Tuovinen, J.-P., Valdebenito, A., and Wind, P. (2012) The EMEP MSC-W chemical transport model — technical description. Atmospheric, Chemistry and Physics, 12: 7825-7865.

UNEP/WMO Integrated Assessment of Black Carbon and Tropospheric Ozone
http://www.unep.org/dewa/Portals/67/pdf/Black_Carbon.pdf

Malé Declaration on Control and Prevention of Air Pollution and its likely transboundary effects for South Asia.
http://www.rrcap.ait.asia/male/

Climate Change And Clean Air Coalition
http://www.unep.org/ccac/

UNECE LRTAP Hemispheric Transport of Air Pollution (HTAP) 2010 Assessment
http://www.htap.org/
West, J.J. and Emberson, L. (2010) Chapter 5: Impacts on Health, Ecosystems and Climate. In: Hemispheric Transport of Air Pollution 2010. Part A. Ozone and Aerosols. Eds Dentener, F., Keating, T., Akimoto, H. Air Pollution Studies No. 17. United Nations, 2010.