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Development & application of methods for modelling & mapping ozone deposition & stomatal flux in Europe - AQ0601PP

Ground level ozone is a major air pollutant that, at current concentrations in the UK and Europe, adversely affects forest growth, agricultural production and the composition of semi-natural ecoystems. In the UK, the economic value of ozone-induced wheat yield losses in the year 2000, a year with relatively low ozone concentrations, was estimated to be £144 million. The most recent estimate of arable yield loss in Europe, covering 23 crops, was of a value of £4.5 billion annually. Both national and European estimates do not consider the large impacts on the income of individual producers of sensitive crops in areas with high ozone concentrations. Furthermore, these estimates do not account for effects on productive grasslands, fruit trees, non-food crops, and other important categories. To date, no estimate is available of the impacts of ozone on UK or European vital ecosystem services, e.g. carbon storage and biodversity.
Within Europe, through the activities of the European Union (EU) and the UN/ECE Convention on Transboundary Air Pollution (CLRTAP), there is active discussion of policy measures to reduce emissions of precursors of ozone formation and hence its environmental impacts. Assessment of the impacts of ozone, and the benefits of emission control policies, requires complex computer models to operate at a European scale. This is because ozone spreads in high concentrations over large areas, and can be transported over hundreds of kilometres. Effective representation in these models of the processes by which ozone is deposited to vegetated surfaces is important for two reasons. Firstly, the total deposition of ozone to the ground is an important process by which ozone concentrations are reduced. Secondly, uptake of ozone through the stomata (tiny pores on leaf surfaces) is the main route by which ozone reaches sites of damaage within plants.
In this project, we aim to further develop and apply a computer model of these processes of total deposition and stomatal uptake of ozone to vegetation. This DO3SE (Deposition of Ozone and Stomatal Exchange) model has been accepted as the best model available and 'fit for purpose' for assessing ozone deposition and risks of damage to vegetation at a European scale for policy assessment within CLRTAP.
DO3SE is also part of a much larger computer model including complex air chemistry and meteorology which is operated by the European Measurement and Evaluation Programme (EMEP) and which is used by both CLRTAP and the EU to assess the benefits of policies to control emissions from motor vehicles, industry and other sources of the precursors which lead to ozone formation. Although the use of DO3SE for UK and European-wide risk assessment is well established, its limitations and weaknesses might have important implications for assessment of ozone impacts and control measures both in the UK and across Europe. In this project, we will focus on four specific and important aspects to further improve the DO3SE model.
Firstly, we will improve the model for application to grasslands, which are important both economically and in terms of conservation. While the DO3SE model works well for agricultural crops and commerical forests, which are dominated by one plant species, we need to further develop it to apply to grasslands with a mix of species. We will develop a general form of the model for such plant communities and two versions of the model to apply to particular types of grasslands. The first are productive, well fertilised grasslands in which ozone reduces the proportion of clover compared to grasses. The second are species-rich grasslands, in which ozone may reduce the cover of species of conservation value. We will work with colleagues in other projects (some supported by Defra) to estimate the possible effects of ozone on such grasslands.
Secondly, our model of ozone deposition and stomatal uptake needs to include two important factors - the phenology (timing of growth stages) for different types of vegetation (because we need to know how this relates to periods with high ozone concentrations) and the wetness of the soil (because in dry soil, the stomatal pores close and less ozone is taken up). The formation of ozone is controlled by climate and ozone levels are highest in hot dry periods. We need to ensure that our model provides good predictions of plant growth stage and soil moisture to properly assess the effects of such ozone episodes. We will develop an improved version of the model with better treatment of phenology and soil moisture and will use both local datasets and European-wide data to check that our new model provides good predictions.
Thirdly, our model is written in FORTRAN (F), which ensures time-efficient modelling of ozone fluxes and deposition for large spatial areas and time periods, but also means that few other scientists and policy makers can use the model because they don't know this programming language. We will therefore create a 'user interface' through which specific features of the model can be changed and the effect of such changes assessed. This will allow scientists and policy-makers to easily compare predictions of the DO3SE model with the values we use for European scale work with local values which are more relevant in their countries.
Finally, there is strong experimental evidence that plant foliage exhibits variable capacities to detoxify O3 taken up into the leaf interior and to repair ozone-induced damage due to varying concentrations of anti-oxidants at the cell wall. Based on measured datasets for wheat we will therefore develop a detoxification module for the DO3SE model, which will enable us to predict rates of detoxification as a function of environmental conditions. In a last step, the implications of a variable, compared with a fixed, flux threshold for modelled ozone fluxes to wheat will be assessed using the DO3SE model.
The work programme is divided into four major Work Packages; the policy and scientific rationale for these specific areas of work are summarised in Section 7c. In addition, options for two additional Work Packages are briefly presented at the end of Section 7c. The major aim, and specific objectives, of the four major Work Packages are as follows:-

Work Package 1: To develop the DO3SE model for application to semi-natural communities

1.1 To develop a generic version of the DO3SE model for grassland communities, comprising different component fractions of up to three functional groups (grasses, forbs and legumes).
1.2 To parameterise specific versions of this model for productive grass/clover swards and for U.K. grassland communities of high conservation status.
1.3 To develop methods to derive relationships between modelled O3 flux and yield, species composition and ecosystem function in U.K. grassland communities.
1.4 To apply the flux and flux-response models developed in 1.1-1.3 to assess O3 impacts on grassland communities at U.K. and European scales.

Work Package 2: To develop and evaluate DO3SE estimates of seasonal variation in O3 deposition and flux.

2.1 To identify and parameterise suitable phenological and SMD models for incorporation into the DO3SE model for European and U.K. species and species groups.
2.2 To evaluate and compare the phenological and SMD models using a variety of data sets (site-specific and remotely sensed) and comparisons with other models for key species, species groups and locations across the U.K. and Europe.
2.3 To assess the influence of phenology and SMD on modelled total O3 deposition and stomatal flux under variable meteorological and O3 concentration conditions across the U.K. and Europe.

Work Package 3: To develop a user interface for the DO3SE model

3.1 To develop a user interface of the F-coded DO3SE model, that will provide the scientific effects and policy communities with the capability to perform their own (local-scale) flux based risk assessments.
3.2 To ensure a wider and more accurate application of the DO3SE model and to increase the number of model evaluations performed.
3.3 To increase the application of the DO3SE model to national and pan-European policy assessments for O3

Work Package 4: To develop a detoxification module for the DO3SE model

4.1 To further develop the DO3SE model for wheat by incorporating a module that predicts rates of variable detoxification
4.2 To assess the implications a variable flux threshold will have on the modelling of ozone fluxes to wheat using the DO3SE model
Project Documents
• Annual Report : Annual Report, April 2007 - March 2008   (3355k)
• Annual Report : Annual Report, April 2008 - March 2009   (3435k)
Time-Scale and Cost
From: 2007

To: 2012

Cost: £338,425
Contractor / Funded Organisations
Stockholm Environment Institute
Air Quality              
Ecosystem Functioning              
Environmental Protection              
Fields of Study
Air Quality