Environmental Modifications Of Responses Of Grassland Species To Tropospheric Ozone

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Environmental Modifications Of Responses Of Grassland Species To Tropospheric Ozone

Section I

Grasslands of the world and Europe

Neutral grasslands occur throughout the United Kingdom on soils in the pH range of 5 - 7. By definition, these are neither strongly acidic as with heathlands nor strongly alkaline as with chalk grasslands.

Grasslands growing on acidic and calcareous soil are of high conservation and amenity value. These systems, particularly calcareous grasslands, have a high diversity of wild flowers and plants, including rare plant species. Today, many of these grasslands receive high rates of nitrogen pollution.

Grasslands accumulate much pollutant nitrogen despite a long history of nitrogen deposition. Much of this nitrogen is rapidly immobilised (locked away) in the soil. This reduces the amount of nitrogen leaching away in groundwater.

Nitrogen pollution causes a decline in the attractive flowering plants, such as the wild thyme. This results in an increase in the dominance of just a few grasses and sedges. Nitrogen pollution therefore may reduce the conservation value of these grasslands in the long term.

The ecosystems can store pollutant nitrogen. However, continued high nitrogen deposition threatens the diversity of plants in these important ecosystems. The empirical data from our research are of direct relevance to policy makers setting critical loads for these systems.

Section II

Tropospheric Ozone

The non-linear nature of ozone production and loss requires the use of sophisticated chemical transport models to assess the effectiveness of actual and potential control measures. The aim of the project was thus to develop and improve predictive models for application to the formation of tropospheric ozone on a range of different geographical scales (i.e. global, regional and national). This overall project aim has been achieved.

No one model is capable of covering ozone formation on all the required scales from urban to global at a high spatial resolution or with the detailed treatment of chemistry and meteorology required. Thus, different but linked models are needed, as shown in Figure 1. As part of the present project, improvements have been made to existing models, such as STOCHEM or the Photochemical Trajectory Model, in terms of the chemical mechanisms or the emission inventories used. In addition, two new models - EUROSTOCHEM and the Ozone Source Receptor Model (OSRM) - have been successfully developed for application to the formation of tropospheric ozone and its control. The EUROSTOCHEM model provides greater spatial resolution than can be achieved using the parent STOCHEM model. The Ozone Source Receptor Model has been designed to supplement the ELMO model in some applications as it uses more realistic air mass trajectories.

Figure 1 A Schematic Overview of the Spatial Domains covered by the Different Ozone Models Used in the Project, the Specific Activities Undertaken and their Relation to the 6 Main Project

Task Areas.

Global/Regional Modelling

Previous modelling work by the Meteorological Office using the STOCHEM global tropospheric chemistry model had indicated that the global ozone circulation could have a significant impact on regional ozone concentrations. The work had concluded that rising global ...