Grayling emissions omission admission: Heathrow air quality costs 2-4 times higher than previously thought

The Commons Transport Committee is currently assessing the Heathrow proposals for a 3rd runway. One of the issues in which they have taken a particular interest is whether the right numbers have been used for the cost to human health of air pollution, and if the costs of pollution beyond a 2km band around the airport have been properly considered. Chris Grayling, Transport Secretary, has now written to the Committee to clarify the government position, and has confirmed that the DfT omitted (in error) to consider the emissions beyond 2km. By contrast the DfT’s own impact appraisal had noted impacts well beyond this 2km boundary, in terms of additional vehicle traffic.  The total figure for the extra cost to health, from Grayling’s admission, is now thought to be 2 to 4 times higher than the one published in the official appraisal document.  That means the “net present value” of the scheme, previously assessed as minus £-2.2 to plus £3.3 billion over 60 years (so already potentially negative) could drop to as low as minus £-2.6 to plus £2.9 billion under the new estimate.  The cost of the damage to human health from additional air pollution, associated with a new runway, is one of the two ways the DfT assesses the cost-benefit analysis of the proposal. 


Heathrow air quality costs two to four times higher than previously thought, says minister

In the final few weeks of the Transport Committee’s scrutiny of the Government’s proposals for Heathrow expansion, Transport Minister Chris Grayling has written to the committee admitting that the air quality cost of expansion that was presented alongside the draft National Policy Statement (NPS), failed to include any costs beyond a 2km radius of the airport. Their own analysis had elsewhere assessed the impact of additional vehicle emissions well beyond this boundary.

The ongoing air quality barrier to Heathrow expansion

The issue of air quality has long been a sticking point when it comes to Heathrow expansion. Modelling conducted when a third runway was last on the table over a decade ago claimed that by now London would be compliant with legal limits for nitrogen dioxide. But even without an additional runway, the hoped-for improvements turned out to be over-optimistic and London remains in breach of the limits.

A series of successful legal actions against the Government for failing to get to grips with the issue and a focus by the London Mayor on the need for new measures in the capital have recently pushed the issue up the political agenda just as the Heathrow vote begins to loom. Several local authorities close to the airport, together with Greenpeace, have committed to legally challenge the NPS, if adopted in its current form by a Parliamentary vote scheduled for the second quarter of this year. The challenge is likely to centre around air quality, as well as the ‘legitimate expectation’ of communities who believed previous government commitments that expansion was off the agenda.

Legal limits and air quality costs

The Government has assessed the air quality impact of a third runway in two ways.

The first considers what impact the scheme would have on compliance with legal limit values. The latest official position on this, repeated in Grayling’s letter, is that “expansion would be capable of being delivered without impacting the UK’s compliance with air quality limit values”.

As we’ve previously argued, however, it’s hard to feel confident in this scenario, given how many questionable assumptions the conclusion rests on, so it’s no surprise that the NPS does not require air quality limit values to be met as a precondition for Heathrow expansion, and that no air quality enforcement plan has been proposed.

The second approach to assessment monetises the damage to human health of the additional air pollution associated with expansion for inclusion in the cost benefit analysis of the scheme.

The Transport Committee has taken a particular interest in whether the right numbers have been entered into this analysis and has identified that the air quality cost calculation only covered emissions within a 2km radius of the airport in contrast to the Government’s impact appraisal that had noted impacts well beyond this boundary in terms of additional vehicle traffic.

Emissions omission

Acknowledging this “unintended omission”, Transport Secretary Chris Grayling’s letter to the Transport Committee, provides new information on the likely cost of emissions beyond a 2km radius of Heathrow airport, with the total figure now thought to be 2 to 4 times higher than the one published in the official appraisal document. The cost associated with Gatwick expansion was also underestimated, the letter notes.

The Government is keen to argue that even the revised figure pales in comparison with the supposed benefit of the scheme, but closer inspection of this claim using other official metrics tells a very different story. The ‘net present value’ of the scheme, previously assessed as £-2.2 to £3.3 billion over sixty years (so already potentially negative) could drop to as low as £-2.6 to £2.9 billion under the new estimate.

Are we underestimating airports’ air quality impact?

Meanwhile, some academics have questioned whether traditional approaches to estimating airport emissions underestimate the emissions from aircraft themselves. While most studies on airport air pollution have focussed on sites close to the airport, a 2014 paper considering the air pollution impact of Los Angeles Airport found a twofold increase in particulate pollution as a result of the airport’s operation within a 60 km2 radius. It concluded that “the air quality impact areas of major airports may have been seriously underestimated” – a finding as relevant to any other major UK airport as to Heathrow, and casting doubt on the relevance of the 2km radius used in the Government’s NPS assessment.

Are MPs’ in a good position for a summer vote on Heathrow?

Commenting on the publication of Chris Grayling’s letter, AEF’s Deputy Director Cait Hewitt said:

Yet again, the Government’s evidence on the impact of Heathrow expansion on the environment and public health has been found to be lacking. With no climate change policy for aviation, poor information on noise impacts, and unreliable information on air quality, we’re urging MPs to vote against a bigger Heathrow.

Related articles

Seven air quality reasons not to expand Heathrow

AEF briefing highlights inadequate measures to address air quality in Heathrow NPS



Grayling’s letter:

Transcript of the oral evidence session when Grayling spoke to the Transport Committee on 7th Feb 2018


Transport Committee inquiry into the Airports NPS

where there is a lot where MPs express their concerns about Heathrow and air pollution.



see also

Study from Los Angeles shows extent of spread of particle air pollution downwind of airport (implications for Heathrow?)

A study in California looking at air pollution from Los Angeles International Airport has shown far more widespread impacts that had previously been expected. The scientists measured the spatial pattern of particle number (PN) concentrations downwind from the airport with an instrumented vehicle that enabled a larger area to be covered than allowed by traditional stationary measurements. The study found at least a 2-fold increase in PN concentrations over un-impacted baseline PN concentrations during most hours of the day in an area of about 60 km2 that extended to 16 km (10 miles) downwind and a 4- to 5-fold increase to 8–10 km (5–6 miles) downwind. Locations of maximum PN concentrations were aligned to eastern, downwind jet trajectories during prevailing westerly winds. They found the levels of PM miles from the airport were higher than those from motorways. They say “The freeway length that would cause an impact equivalent to that measured in this study (i.e., PN concentration increases weighted by the area impacted) was estimated to be 280–790 km) “The total freeway length in Los Angeles is 1500 km. These results suggest that airport emissions are a major source of PN in Los Angeles that are of the same general magnitude as the entire urban freeway network. They also indicate that the air quality impact areas of major airports may have been seriously underestimated.”

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