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Modelling tropospheric ozone - phase II - AQ0704

Description
The concentrations of ground-level ozone, a pollutant that affects human health, ecosystems and materials, widely exceed environmental quality standards across the UK and Europe. Ozone is not emitted directly into the atmosphere, but is a secondary photochemical pollutant formed in the lower atmosphere from the sunlight-initiated oxidation of volatile organic compounds (VOCs) in the presence of nitrogen oxides (NOx). Elevated concentrations of ozone over the UK are especially generated when slow-moving or stagnant high pressure (anticyclonic) weather systems occurring in the spring or summer bring in photochemically reacting air masses from mainland Europe.

Under conditions characteristic of photochemical pollution episodes, the formation and transport of ozone can occur over hundreds of kilometres, with concentrations at a given location influenced by the history of the airmass over a period of up to several days. In addition to this, the increasing levels of ozone in the free troposphere on a global scale, as a result of climate change and other factors, also influence regional scale photochemical processes by providing an increasing background ozone level upon which the regional and national scale formation is superimposed. This effect now has to be considered when assessing whether proposed air quality standards for ozone are likely to be achieved.

The non-linear nature of ground-level ozone production requires the use of sophisticated chemical transport models to understand the factors affecting its production and subsequent control. The Ozone Source-receptor Model (OSRM) will be the main modelling tool used to meet the Department's spatial and temporal requirements. It has been shown to be a robust and appropriate tool for policy applications. The OSRM will contribute to the forthcoming reviews of international protocols and Directives and will assess the effectiveness of proposals brought forward under the European Commission's Clean Air for Europe thematic strategy.

Over the years, Defra and the Devolved Administrations have supported the development of near explicit photochemical reaction schemes, especially that of the Master Chemical Mechanism and the related Common Representative Intermediates mechanism. This was in recognition that a more targeted approach on ozone precursor emissions would bring greater environmental benefits than a simple percentage mass reduction. The Department and the Devolved Administrations wish to continue their support for this work but have requested a review in the initial phase of the proposed project to identify the future priorities for work on this topic.

In the previous contract (Modelling of Troposheric Ozone, EPG 1/3/200), there was a stronger emphasis on model application to evaluate planned and proposed policies, such as the Review of the Air Quality Strategy. In addition, new tasks were identified: (a) Technical assistance was provided to fulfil commitments arising from the implementation of European Directives and in particular, the 3rd Daughter Directive on Ozone, and (b) Work was undertaken to move from the current AOT metrics for protection of ecosystems to a more realistic flux-based approach and a module to calculate ozone stomatal fluxes has been successfully developed. The work programme for this contract retains many of the work areas but there is a clear shift in emphasis from chemistry to meteorology, with the inclusion of new objectives on using multiple air mass trajectories in ozone modelling and understanding the influence of meteorology on ozone concentrations. The objectives for the new project are:
Objective 1: Policy Development and Scenario Analysis (using the OSRM)
Objective 2: Detailed Assessment of the Relationship between Ozone, Nitrogen Oxide and Nitrogen Dioxide Levels, and Factors controlling them
Objective 3: Improvements to Photochemical Reaction Schemes
Objective 4: Development of Multi-trajectory Modelling Capacity using Forward Track Trajectories

Two additional Objectives were not taken up by the Department in the current contact:
Objective 5: Further development and integration of stomatal flux calculations for crops and semi-natural vegetation
Objective 6: Investigation of the impact of meteorology on ozone modelling

However, at the invitation of the Department, we include a new Objective 7 as a Variation to the Contract:
Objective 7: Costs, Benefits and Trade-offs: Volatile Organic Solvents

To meet the new requirements, we have created a project team involving leading UK practitioners with international reputations in the scientific fields of relevance to ground-level ozone production and control. The key benefit to Defra and the Devolved Administrations is the use of robust ozone modelling tools for policy applications based on the latest scientific understanding.
Objective
Objective 1: Policy Development and Scenario Analysis: To use the available tools to assist policy development and to explore different scenarios. Proposals will be brought forward for new air quality legislation, following the adoption by the European Commission of its thematic strategy on air quality (the Clean Air for Europe, CAFÉ, strategy). In addition, the National Emissions Ceilings Directive will be revised during 2006/07 and the UN/ECE Gothenburg Protocol at a later point. The tools will be needed to evaluate any proposals to modify UK emissions limits in these international agreements.
• National and International Policy Development:
- to use the available tools to show impacts of planned and proposed policies on ozone levels, against national or international objectives and standards, and any other objectives that are agreed or amended during the course of the contract.
- to estimate changes of ozone concentrations at the regional, national and local scales. The modelling should also be able to distinguish between regional background concentrations and enhanced or reduced concentrations in urban and suburban locations in the UK.
• Support for Policy Implementation:
- to use the modelling tools to guide policy formulation, by identifying the extent and location of VOC or NOx control required to meet current or proposed objectives or standards. Modifications may be needed to the ozone modelling tool to enable its use in this second mode,
- to develop optimum implementation strategies to abate VOC and NOx to maximise the reduction in ozone and NO2 concentrations, for agreed or proposed meeting emission ceilings.
• 3rd Air Quality Daughter Directive Reporting:
- to provide outputs from the ozone modelling tools to supplement measurements from ozone monitoring sites to meet requirements under the Third Daughter Directive. The Directive requires an assessment of ground level ozone concentrations throughout the UK using measured data and modelled outputs where appropriate. Data need to be reported to the Commission on an annual basis by the 30th September each year.
Objective 2: Detailed Assessment of Relationship between Ozone, Nitrogen Oxide and Nitrogen Dioxide Levels, and Factors controlling them: To investigate the relationship between levels of ozone (and other oxygen species) and NOx at the urban scale, in particular during photochemical events, in order to support future policy developments that may affect local NOx/NO2 partitioning and ozone concentrations.
• to identify the role of biogenic VOCs and the OH radical during such episodes, together with the impact of increased direct NO2 emission (for example as a result of vehicular emission control technology).
• to justify the choice of model, paying particular attention to the resolution to be applied.
• to compare the NOx/NO2 partitioning calculated using the ozone models here, with that calculated using the empirical approach of the National Modelling of NO2, undertaken by John Stedman at Netcen.
Objective 3: Improvements to Photochemical Reaction Schemes: Defra and the Devolved Administrations have funded the development of the Master Chemical Mechanism (MCM v3.1), a comprehensive chemical model describing the chemistry of 135 VOCs and which has become a benchmark in the chemical modelling community. MCM 3.1 is currently available on the internet.
• to continue to make the MCM available on the internet.
• to undertake a review of the MCM and CRI within the first nine months of the contract
• to recommend options for its further development.
Objective 4: Development of Multi-trajectory Modelling Capacity using Forward Track Trajectories: The version of OSRM currently being used by Defra and the Devolved Administrations for policy development and impact assessment uses single two-dimensional trajectories.
• to use multiple three-dimensional trajectories (for example, the forward track trajectories now available from the Met Office Lagrangian NAME dispersion model) within the chosen ozone modelling tools.

In addition, the Department included two further objectives as options in the original Invitation to tender that were not taken up:
Objective 5: Further development and integration of stomatal flux calculations for crops and semi-natural vegetation.

Objective 6: Investigation of the impact of meteorology on ozone modelling:

The Department invited a proposal for an extension to the project in November 2007 covering an additional Objective 7:
Objective 7: Costs, Benefits and Trade-offs: Volatile Organic Solvents. The purpose of this objective will be two fold:
• to develop a methodology for assessing the costs and benefits of solvent reduction and substitution policies. The methodology should enable full life cycle analysis of alternative approaches to inform and underpin future policy development to meet domestic and international commitments.
• To feed into current review of the Master Chemical Mechanism (MCM)

The methodology and relevant timescales by which these objectives are to be achieved are described in the following section on Approaches and Research Plan.
Project Documents
• Annual Report : Modelling of Tropospheric Ozone Annual Report: 2008   (12048k)
• Annual Report : Modelling of Tropospheric Ozone Project Summary Report: 2007-2009   (1658k)
• Other : VOCs and climate change   (589k)
Time-Scale and Cost
From: 2007

To: 2011

Cost: £1,027,184
Contractor / Funded Organisations
AEA Technology
Keywords
Air Pollution              
Environmental Protection              
Modelling              
Pollution              
Fields of Study
Air Quality