When the UK government announced in June that members of parliament had voted in favour of building a third runway at London Heathrow, it threw in the caveat that final development consent would be granted only if the expansion could be delivered within the country's existing air-quality obligations.
The UK is already in breach of the EU 2008 Directive on Ambient Air Quality for nitrogen-dioxide concentrations – as are several other EU member states – and Heathrow is under pressure to prove that it can put enough mitigation measures in place to expand sustainably.
Additionally, there are signs that the goalposts may shift and air-quality limits could become even more stringent. Not only could this make Heathrow's case more difficult to prove, it might also create challenges for other airports located away from heavily congested cities, in areas previously thought to have safer levels of air pollution.
In a September 2018 report on the effectiveness of air quality standards, the European Court of Auditors said that while EU policies had contributed to emissions reductions, air quality "has not improved at the same rate and there are still considerable impacts on public health". According to the World Health Organization, air pollution causes about 400,000 premature deaths a year in the EU. The pollutants responsible for most of these deaths are nitrogen dioxide, particulate matter, and ground-level ozone.
The report concludes that the EU's air quality standards, which were set nearly 20 years ago, are no longer in line with the latest scientific evidence on human health impacts. The European Court of Auditors' recommendation to the European Commission is that it considers carrying out "an ambitious update of the Ambient Air Quality Directive, which remains a significant instrument to make our air cleaner".
If such an update takes place, airports that had previously thought they could expand without breaching local air-quality limits might find that this is no longer feasible. "If there are more stringent limits, we could see other airports caught out," says Tim Johnson, director of the Aviation Environment Federation. "Different thresholds could mean areas we thought were safe aren't, and this brings different airports in."
The AEF is calling on the UK government to update evidence on air quality near airports around the country, so it is easier to see which ones could face issues in the future. "In 2002/3, Labour [the party then in government] commissioned an analysis of air quality around UK airports. Heathrow was top of the list [for poor air quality in the surrounding area] but other airports weren't ringing any alarm bells. In the last 15 years there has been nothing to update that," says Johnson.
"We want to ask the government to update the evidence base so we have a better feel for air quality [around airports]... so we can see which airports are close to or exceeding [limits]."
Despite these concerns, Heathrow has "a very high" level of confidence that its planned expansion can be delivered within the current air-quality limits, says the airport's head of emissions strategy Andrew Chen. While issues such as the UK's "continued noncompliance with EU limits are at the forefront of our mind", Chen notes that "big step-changes have been made that have given us confidence".
However, he adds that if the EU were to tighten its air quality standards, "our job [would be] to reassess and come up with additional measures to ensure" that the third runway is still environmentally deliverable.
In its Heathrow 2.0 sustainability strategy, the airport outlines the steps it will take to improve local air quality. These include introducing an "airside ultra-low emissions zone" by 2025 and working to ensure that, by 2030, half of all journeys to and from the airport are made using public transport.
Heathrow is targeting a 40% reduction in nitrogen oxides (NOx) – "the pollutant of most concern", says Chen – from airport-related road traffic by 2020 and a 60% reduction by 2025. Its target for airside vehicles is "more ambitious", Chen acknowledges, and involves halving NOx emissions by 2020 and cutting them 70% by 2025.
The airside target is easier to reach because the airport has more control over these vehicles. Attempts to reduce emissions from diesel-powered cars and vans outside the perimeter, however, will largely depend on action from local authorities, the government and the general public. Heathrow has committed to converting all of its cars and small vans to electric or plug-in hybrid by 2020, and the airport is hoping that vehicles outside of its control will follow suit.
"We have to show what's possible, and switching our own fleets sends a strong message. We like to lead by example," says Chen. "In December we installed six rapid chargers in our taxi zone, and we're trialling a newer form of rapid electric charging for our private-hire vehicles." Earlier this year, Heathrow teamed up with Jaguar to provide a zero-emissions chauffeur service, which will deploy a fleet of up to 200 Jaguar I-PACE electric cars on journeys to and from the airport.
Heathrow argues that improvements to the public transport network will reduce the number of people travelling to and from its doors by car. For instance, Chen says the new Crossrail line – scheduled to open next year – will be "transformational", and will "dramatically increase the number of people who can get to the airport within an hour".
Further into the future, the HS2 high-speed railway line linking London with the north of England, as well as other planned rail projects to the south and west, will put Heathrow "at the centre of connectivity for north, south, east and west", he adds.
Coaches will also play a bigger role in transporting passengers from urban areas across the country. "We've made strong commitments in Heathrow 2.0 on making sure we're connected to the UK's largest 100 towns and cities, and a big part of that will be delivered by coach. We're working diligently on bringing in new coach services," says Chen.
"With the improvements we can make today and in the future, we're very confident in our ability to meet those [air quality] limits," he notes. Chen goes as far as to add: "Even with the conservative assessments done by government agencies and without our initiatives, this can still be achieved."
But others are not so confident. With the UK – and in particular, London – already failing to meet air-quality targets, some find it difficult to see how the situation could improve enough to not only ensure that these targets are met, but to create the extra wiggle-room to allow for the 240,000 additional annual aircraft movements and related journeys that the third runway would bring.
"The concern we've expressed is that it's very difficult to have confidence that we can get from where we are now to the mid-2020s and the government would have been so successful that it can create the headroom [for Heathrow's expansion] and still be within legal limits," says AEF deputy director Cait Hewitt. "The policy process through which Heathrow's expansion is delivered gives Heathrow responsibility for tackling emissions, but Heathrow hasn't got the power to get to grips with the fuel source being used by vehicles in London.
"Heathrow has said its goal is no increase in vehicle traffic... It's unclear how that commitment can be delivered because there's a problem with accountability and enforcement."
Chen says Heathrow is "working in partnership" with local councils to improve air quality outside the airport fence, and it "stands firmly behind" the London mayor's plan for an ultra-low emissions zone in the capital. But that support does not appear to be reciprocal.
London mayor Sadiq Khan – who supports expansion at London Gatwick rather than Heathrow – said in June that he would join legal action brought by local councils against the third runway on air quality grounds. The mayor said at the time that a third runway at Heathrow would "lead to even higher levels of toxic air in an area where pollution is already well above legal levels for NO2 emissions".
Another issue which Hewitt believes could become more significant going forward is the effect on human health of ultra-fine particulate-matter emissions. "The focus has been on nitrogen dioxide but, in terms of health impact, particulate matter looks increasingly problematic. This might change how much aircraft themselves are responsible [for local air pollution] compared to traffic," she says, adding that particulate matter from aircraft engines "might turn out to be a bigger issue".
Chen disagrees, and says emissions from aircraft result in "quite a limited amount of offsite pollution to local communities". Heathrow, therefore, is placing heavy focus on trying to limit the amount of road traffic outside the airport.
Meanwhile, ICAO is in the process of developing a particulate matter standard for aircraft engines. The proposed standard "mandates that all new and in-production engines certify for nvPM [non-volatile particulate matter] emissions on or before 1 January 2020", says ICAO. It adds that the measure would "address one of the gaps in the ICAO engine emissions standards", align aviation with other modes of transport, and "lead to a better assessment of nvPM impacts".
Heathrow "welcome[s] the nvPM standard for aircraft engines", says Chen. "But it's important to note that the contribution of aircraft emissions [to] air quality where people live is relatively limited". However, he points to concerns about the health of airside employees, which could be addressed by the standard.
"This standard is the first for particulate matter on aircraft... It's not necessarily being set to raise the bar for aircraft manufacturers, it's to set what the bar is," says Chen, adding that this bar could be tightened later on, with possible input from aviation industry stakeholders. When it came to noise standards for aircraft, he highlights Heathrow's "gatekeeping influence", suggesting that the Airbus A380 "is as quiet as it is because of our ability to influence".
The airport is hopeful that this influence can also be applied to the large numbers of airline passengers that pass through its doors every day. For instance, green initiatives that are visible at the airport have the potential to trigger behavioural changes in this captive audience, believes Chen: "Our gatekeeping influence is not just for aircraft, it's for people as well. There are millions of people coming to our doors that we have the ability to influence, and there are a number of things we can do.”
For example, a recent agreement with car-sharing network Zipcar to trial the use of electric vehicles on various journeys to and from Heathrow's Terminal 5 "gives passengers the chance to try an electric vehicle for the first time, and this might influence their future decisions".
The UK's High Court ruled in early October that hearings on five legal challenges against Heathrow's expansion – including the one supported by the mayor of London – would take place in March 2019. The airport's long-running battle for permission to expand is far from over.