Air pollution is the crucial barrier to the expansion of Heathrow, and the issue has received a great deal of Government attention. Government's policy is clear:
…another runway at Heathrow could not be considered unless the Government could be confident that levels of all relevant pollutants could be consistently contained within EU limits.10
The UK regulations implementing the Air Quality Directive came into force in 2001 and were updated in 2003. The limit of 40 µg/m3 took immediate effect, although ‘margins of tolerance’ were also specified. These reduce each year until 2010, when the limit of 40 µg/m3 will be absolute. So in practice the limit was 54 µg/m3 in 2003, 52 µg/m3 in 2004, 50 µg/m3 in 2005, and so on. At monitoring sites close to the airport these limits have been breached in every year since 2003. The air pollution monitoring station closest to Heathrow have shown the following pollution levels:
annual mean NO2 (μg/m3)
Before the White Paper consultation, the Government commissioned modelling of the likely impacts on air quality of a variety of expansion scenarios at Heathrow. This work, ‘the SERAS work’,11 predicted that if expansion went ahead without significant mitigation efforts, large numbers of people would be exposed to illegal levels of NO2 by 2015 – around 20,000 in mixed mode, and around 35,000 if a third runway were added. It was found that by modelling the effects of ever more ‘determined action’, using assumptions developed in consultation with key players from the aviation industry, this number could be reduced to 5,000.
The reports that support the current round of consultation represent a fine-tuning of these models, based on more detailed understanding and assumptions. However just about every assumption going into these models is contentious and adds to the uncertainty of the predictions. The reports being consulted on are honest about the uncertainties in the modelling and clear about where these are. The problem is that the total uncertainty arising from the model assumptions may well exceed the difference between the modelled levels of air pollution and the EU air quality limit. Table 2 discusses some of the sources of uncertainty. They include the following:
10 ATWP 11.54
11 Modelling was carried out by AEA Technology with consultants Halcrow Ltd, who reported to South East and East of England Regional Air Services Study (SERAS).