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Executive Summary

1. This Report sets out the work and findings of the technical Panels set up by the Department for Transport in 2004 to advise the Government on ways to strengthen and update the assessment of air quality around Heathrow Airport, following publication of the Air Transport White Paper "The Future of Air Transport" in December 2003. It records the Panels' review of available evidence and measurement data. It gives their analysis of existing methodology and modelling. Above all, it sets out their conclusions and recommendations on how best to assess air quality at the airport in future years, including the modelling tools and assumptions to be used.

2. There is an accompanying report of an independent peer review panel whose task was to review the process established to deliver the air quality advice and whether the resulting technical report took appropriate account of the current state of scientific knowledge, whether its conclusions were clearly and fairly presented, were justified in light of the current state of knowledge, and were appropriately comprehensive and fit for purpose.

3. Together, the reports provide the basis for the next phase of the work by the Department, on the generation of emissions inventories and revised modelling of future air quality at Heathrow. This in turn will inform further assessment of the likely impacts of any further development at Heathrow, and whether measures are available to ensure that any further development meets the conditions laid down in the White Paper. The results will form part of a further public consultation in due course before Government announces any conclusions.

Background and rationale

4. The White Paper "The Future of Air Transport", identified the need for a national strategic framework for the future development of airport capacity in the United Kingdom, looking forward 30 years. One reason given in the White Paper for this strategic framework was the requirement to address the environmental impacts that air travel generates.

5. The White Paper noted the Government's support for a third runway at Heathrow once it could be confident that the key condition relating to compliance with air quality limits can be met. It was judged that there was a substantially better prospect of achieving this if development of a third runway and terminal capacity was deferred until the 2015-2020 period, as long as action is taken meanwhile to tackle the NO2 problem. The Government's support is also conditional on measures to prevent deterioration of the noise climate and improve public transport access.

6. The White Paper said that the Government would institute, with the airport operator and relevant bodies and agencies, a programme of action to consider how these conditions can be met in such a way as to make the most of Heathrow's two existing runways and to enable the addition of a third runway as soon as practicable after a new runway at Stansted. This commitment is being taken forward through the Project for the Sustainable Development of Heathrow (PSDH). PSDH will help determine whether further development is likely to be consistent with the environmental conditions laid down in the White Paper. In other words it addresses the commitments made in the White Paper, but does not authorise or preclude development itself.

7. A number of organisations are involved in taking forward PSDH, including the airport operator BAA, the National Air Traffic Services (NATS), the Civil Aviation Authority (CAA), airlines, DfT Rail (formerly the Strategic Rail Authority) and the Highways Agency. The key areas of work for PSDH are air quality, surface access, mixed mode operations and aircraft noise.

Panel Remit for Air Quality

8. In 2004 as part of PSDH, the Department for Transport's Aviation Environmental Division set up three Panels of air quality-related experts. The Panels were to advise the Government on ways to strengthen and update the air quality assessment of Heathrow Airport, as undertaken for the White Paper. The focus of the work of the Panels has been on providing guidance to DfT on the tools to assess air quality at Heathrow Airport. It is the Government who will then use this guidance to re-assess current and future scenarios for Heathrow development, up to the year 2030. The guidance is not necessarily transferable to other UK airports but is acknowledged to have relevance given the 'state of the art' developments emerging in some areas of the technical panel work.

9. The Panels, have met frequently since summer 2004, and covered:

• dispersion modelling (Panel 1);
• monitoring of air pollution (Panel 2); and
• emission source data (Panel 3).

10. Each panel consists of scientific and technical experts specifically invited for their contribution to local air quality understanding at airports. Panels have a balanced membership, including recognised air quality assessors and measurement experts, model users and developers and experts from academic and private research communities. Many of the experts are representatives from recognised best practice working groups, such as Air Quality Expert Group (AQEG), the UK Air Dispersion Model Users Group, and there has been ad hoc representation from the international expert community. Policy makers (Government), London Borough technical representatives, airport and airline operators and road network managers have also been part of the technical panel process.

11. The overall process adopted by the Panels was to:

• review the technical and scientific robustness of previous local air quality assessment work undertaken by the DfT for Heathrow;
• review the evidence available to refine future assessments, including accounting for new and emerging best practice and changes to assessment requirements;
• identify and specify research and other work needed to improve understanding of air quality assessments;
• examine the adequacy of measurements of airborne pollutants from different sources around Heathrow for verification of models and also for compliance with standards;
• perform innovative analysis of existing data to gain further understanding of key issues and ways forward;
• commission / undertake additional data collection or analysis to assist in current understanding of issues or to improve available methods;
• review the suitability and adequacy of previous and currently available emission source data;
• commission / undertake expansion or enhancement of emission source data to assist in current understanding of issues or to improve available methods for future use;
• consider the suitability and adequacy of previous and currently available dispersion models used to represent local air quality around airports;
• identify, specify, commission and analyse an inter-comparison of potential modelling approaches for use at Heathrow - focused on the effect of different approaches to key dispersion issues; and
• agree the appropriate tools and data to be used in further air quality modelling to be undertaken by the Government, in light of commitments made in the White Paper.

12. Whilst the Panels have reviewed other pollutants, the focus of the work has followed the commitment in the White Paper, and has focused on human health related air quality standards. The primary focus has therefore been on annual average concentrations of nitrogen dioxide (NO2) and secondly by particulate matter (PM10).

13. No specific timetable was given in the White Paper for the outcome of this work. However, when the Panels were convened, they agreed to aim to complete the guidance within two years.

14. The work of the three technical Panels has been the subject of an external independent and rigorous peer review process, following the Office of the Commissioner for Public Appointments (OCPA) procedures. A Peer Review Panel (PRP) was established by the Department for Transport in September 2005 to review and scrutinise the work of the Panels and publish conclusions on whether the Panels' work has been clear and fair in establishing a technical basis for future assessments of air quality impacts at Heathrow. All members of the panel were independent from Government and from the institutions providing representatives to the Technical Panels.

Key Conclusions

15. The work of the Panels is outlined in the Project for the Sustainable Development of Heathrow - Report of the Airport Air Quality Technical Panels, 2006. This includes:

• Chapter 1 - a synthesis of the panel process, remit and key findings across all panels set against key questions;
• Chapter 2 - findings from air quality measurements;
• Chapter 3 - recommendations on how to represent sources of emissions; and
• Chapter 4 - findings from modelling the dispersion of air pollution.

16. The output of the three Panels addresses improvements over the relative results of the previous work, by specifying detailed inputs (Panel 2 and 3), model verifications (Panel 1 and 2) and output requirements (Panel 1), as well as improvements in source representation and characterisation (Panels 3 and 1).

17. Overall, the panels found that the key pollutants were nitrogen dioxide (NO2), nitrogen oxides (NOx), and particulate matter (PM10). Ozone (O3) was also included as it is important in the formation of NO2. Panels found that the statutory annual mean NO2 objective was currently being exceeded at some locations around Heathrow. Looking at changes over time, there had been a significant reduction in NOx concentrations over a 12 year period, but the reduction in NO2 over this period had been very small. The Panels found no breaches of any statutory PM10 objectives.

18. It was not the role of the Panels to undertake future year modelling of Heathrow, or to generate the emissions inventory needed to do so. Instead panels have provided detailed recommendations on how best to set a 'bottom-up inventory'. - Given the pollutants and standards shown to be of interest, the inventory setup is focused on calculating annual average concentrations only, and so uses 'representative' diurnal and seasonal profiles for sources. The inventory method has been specifically designed to generate data for base and future years over a long period (from 2002 to 2030).

19. Where possible Panels have included expert judgements of uncertainty against individual issues. However, the quantification of uncertainty across the inventory, and its expected effect on final dispersed concentrations, is well outside the remit of the PSDH Panels. Indeed, it will only be possible once the modelling has been undertaken.

20. The Panels concluded that in general, sources of nitrogen oxides (NOx) emissions are better characterised, and hence inventory methods for NOx are less uncertain, than inventories for particulate matter. Further, emission estimates of aircraft source groups are generally more certain than those for road transport and other airport airside sources (in that order) on account of detailed 'certification' data and performance assessment for the aircraft source.

21. Panel 1 has used 5 different dispersion models in a controlled comparison of a nominal base case to understand the suitability of different approaches. The models include descriptions of pollutant transport by dispersion and advection. Four of the five models used were based on Gaussian dispersion, while the fifth used a Lagrangian particle approach. All models used the same emissions inventory and meteorological data to ensure that the inter-comparison focused on the dispersion elements of the models. Model outputs were compared at a pre-agreed number of receptor points including monitoring sites. Source apportionment was a specific requirement.

22. Model accuracy was assessed through validation against monitoring data. The model inter-comparison indicates accuracies in the range 10 - 20% for the annual mean NO2, well within the EU guidelines for modelled annual mean NO2 of 30%. In addition to comparisons with monitoring data, several 'fitness for purpose' criteria and diagnostic tests were carried out to help assess model performance.

23. Across all models, the Panels found that the modelling of plumes from aircraft during take-off and landing is not well established. Specific problems include plume rise and the effect of wake vortices. Panel 1 recommended areas of improvement to the recommended dispersion model to address these and other issues.

24. Following the model inter-comparison Panels 2 and 3 were in full agreement with Panel 1 in recommending the CERC model ADMS-Airport (a Gaussian dispersion model) for future modelling work at Heathrow. It fulfils all of the fitness for purpose criteria, and was the best performing model for each of the comparison criteria. Like the other models, ADMS-Airport is demonstrably better than the pre-White Paper approach. It was agreed that some limited use of the LASPORT Lagrangian particle model could be useful to test the effects of a different atmospheric transport framework as a sensitivity test, given its use for a number of European airports. It was also agreed that limited model runs using the netcen model might also be appropriate to provide comparisons with earlier analyses, for audit trail purposes for the Department for Transport.

Peer Review

25. The review was carried out by an independent peer review panel (PRP), chaired by Professor Bernard Silverman FRS. Peer review included detailed examination and questioning of the Panel Report findings and statements, and included observation of the panel processes leading to its completion. The key conclusions of the PRP were that:

• the Report takes appropriate account of the current state of scientific knowledge and its application to the subject of the review (whilst acknowledging that certain elements of the most recent work referred to in the Report has so far only appeared in pre-publication format, pending its submission to the standard review processes of scientific publication);
• the conclusions of the Report are clearly and fairly presented;
• the conclusions set out in the Report are justified in light of the current state of knowledge;
• the Report is appropriately comprehensive and fit for purpose;
• the Panels have fairly identified areas where there is uncertainty and/or the potential for specific future research; and
• the discussions at Technical Panel meetings were robust and open; debate was not dictated, or constrained, by either the respective Chairs of those meetings, by the presence of representatives of DfT or of other Government Departments, or by the presence of the PRP members. Decisions were made after proper debate and consideration and were not pre-determined or imposed on the Technical Panel members.

Next Steps

26. Following the reports of the Technical Panels, the Department for Transport will carry out further assessments of air quality at Heathrow, including:

• Collation and processing of recommended emission inventory data, both improved and changed activity data and updated/enhanced emission rate data.
• Production of procedures to translate and enhance data in the activity-emissions-dispersion stages of modelling.
• Creation of the specified emissions inventories for the base year and several future forecast years.
• Enhancement and sensitivity testing of selected model approaches to account for developments within the Panels (such as the improved parameterisation of initial dispersion using results from LIDAR measurement work initiated by the Panels).
• Extensive verification tests of the base year air quality model(s). These include source attribution tests, uncertainty analysis and model performance statistics as well as comparison to monitoring and previous modelling work.
• Future year air quality modelling for a number of different years and development scenarios.

27. The results will inform advice to Ministers and a public consultation exercise in due course before firm decisions are reached on how to make best use of Heathrow's existing two runways, and whether a third runway could be added after a new runway at Stansted, whilst complying with strict conditions on air quality.

Acknowledgements

28. The Department for Transport would like to acknowledge and thank all panel members for their considerable work leading to and including the preparation of this report. Particular thanks go to the Panel chairmen:

• Professor Mike Pilling, University of Leeds (Panel 1);
• Professor Duncan Laxen, Air Quality Consultants Ltd (Panel 2); and
• Professor David Raper, Manchester Metropolitan University (Panel 3).

29. The Department for Transport also recognises with thanks the work of the Peer Review Panel, and the benefits of this process to the final product, and subsequent work arising from it.