The impact of air pollutants on human health has increased in profile over the last few years, largely due to the growing scientific evidence about the level of harm that pollutants such as nitrogen oxides (NOx) can cause. The Royal College of Physicians estimated that poor air quality is linked to approximately 40,000 premature deaths a year in the UK.
The UK’s air quality obligations are set out in the 2008 ambient air quality Directive, which has been transposed into English law by the Air Quality Standards Regulations 2010. The Directive “establishes the need to reduce pollution to levels, which minimise harmful effects on human health.” It also specifies “limits values for the protection of human health” (Annex XI) in respect of certain key pollutants, including an annual mean limit value of 40 μg/m3 for nitrogen dioxide (NO2). Compliance is assessed through measurements carried out by “receptors” placed at the high-polluting areas within a region. A region is deemed to be in breach of the Directive if receptors exceed the limit values.
The deadline for compliance was 2010 but several areas in the UK remain above the limit values, including Greater London where main roads regularly breach legal values for nitrogen dioxide. In the latest compliance report, the UK reported that the limit value for annual mean NO2 was exceeded in 37 out of the 43 zones. Where the limit values remain in breach, there is a duty to adopt measures to ensure that the limit value is achieved as soon as possible. Once limit values are achieved there is a duty to ensure that they are not exceeded again.
In April 2015, the Supreme Court ruled the Government was in breach of its obligation to bring emissions within EU limits and ordered it to publish an updated plan by which compliance would be achieved. This plan was published by the Department for Environmental, Food and Rural Affairs (DEFRA) in December 2015 and forecast compliance within London by 2025 (“2015 Plan”). The plan proposed a range of measures to achieve compliance, the primary means of which was the introduction of ‘Clean Air Zones’ in urban areas. On 2 November 2016, the Supreme Court ruled that the 2015 Plan was based on “optimistic emissions data [and] did not seek to meet the requirements of the Directive as soon as possible” and that the Government must develop a new draft plan by April 2017.”
The revised Air Quality Plan (“2017 Plan”) was published for consultation in May 2017, with the final version published on 26 July 2017. The 2017 Plan for NO2 was required to bring down levels of NO2 to within legal limits in the shortest time possible, as well as reducing exposure as quickly as possible, and to do so in way that meeting legal levels was not just possible but likely - as required by the High Court in 2016. On 7 November 2017 Client Earth launched further legal action on the weakness of the 2017 Plan for NO2. On 21 February 2018, for the third time, the high court ruled that the Government’s current policy on air pollution was “unlawful” and ordered changes. Mr Justice Garnham, who heard the case, said: “The history of this litigation shows that good faith, hard work and sincere promises are not enough, and it seems court must keep the pressure on to ensure compliance is actually achieved.” He noted a “real risk” from air pollution, said the government’s plans were “seriously flawed”.
Air quality reanalysis has been published alongside the revised Airports NPS, with a detailed annex included in the Appraisal of Sustainability. This was done to assess the implications of the 2017 Plan, as well as new demand forecasts, in terms of the NWR’s compliance in relation to EU Directive. The air quality reanalysis supporting the NPS concluded that “with the effective implementation of the Government’s 2017 Plan measures (as represented by the PCM model projections in the 2017 Plan), increased airport capacity will not affect modelled compliance with EU limit values.” The NPS also supports the conclusion that compliance would be reached with the NWR scheme:
The result of this analysis helped inform the Government’s view that, with a suitable package of policy and mitigation measures, including the Government’s modified air quality plan, the Heathrow Northwest Runway scheme would be capable of being delivered without impacting the UK’s compliance with air quality limit values.
What the NPS does not state, however, is that the updated analysis found that its compliance is subject to “uncertainty”. If the NWR were to open in 2026, as is assumed by the DfT in their appraisal, “the risk is high and the option is likely to impact on compliance with limit values due to impacts in central London. The risk falls to medium in 2030.” Although all those road links included within the Heathrow area are predicted to be compliant by 2024, both Heathrow options, increase pollutant concentrations on roads across London which would impact compliance. The reanalysis discussed:
Whilst this increase is small in magnitude, the opening of any option between 2026 and 2030 is coincident with the period over which the Greater London zone moves from non-compliance to compliance in the PCM model projections. As such, concentrations alongside some roads in central London, including the key A40 Westway, sit at or close to the limit value in all years and emissions scenarios and the small impact from airport expansion risks worsening exceedances of limit values on some routes or delaying compliance with limit values.
Because of this, reanalysis also concluded that “there are limited actions that the scheme promoters can take to reduce the impacts of the schemes in central London, and the mitigation of risks relies on the effective implementation of the Government’s 2017 Plan measures and RDE legislation to reduce emissions from road transport.”
The Secretary of State initially said in oral evidence that “mitigation measures are not [considered] in that analysis.” But the air quality analysis is clear that the baseline modelling is based “based on COPERT v5 emissions factors and ongoing measures to improve air quality”. Caroline Low said that it does not take account of anything the airport might do, for example establishing a low emission zone. Even so, it is also clear from the reanalysis that compliance is almost entirely contingent on air quality mitigations at the national level rather than airport level mitigations:
The critical link in all years is the A40 (Westway, 70181) in central London–over 15 km away from the airport boundary. On this road, the impact of the airport is small and the risk of non-compliance is determined to a large degree by the magnitude of the PCM model projection rather than the magnitude of the airport impact.
The NPS states that “failure to demonstrate [compliance] will result in refusal of development consent.” If the Government’s performance on air quality mitigation continues its current unsuccessful trajectory, there is a very real risk that when it comes to DCO approval it may be refused on the grounds of legal air quality compliance. Even if the Secretary of State approved the scheme, there is a strong chance that the development consent would be subject to judicial review and intense scrutiny on the grounds of air quality compliance.
It should be noted that there is very little headroom in terms of compliance in the assumed baseline scenario in the NPS in which the Air Quality Plan 2017 is implemented effectively. For example, the available headroom is less than 5% for the Baseline scenario until 2029. Given the uncertainty of modelling, an underestimate of even relatively small magnitude may delay compliance. The analysis indicated that the overarching uncertainty in the air quality modelling conducted for the Plan was +/-29%. The air quality analysis supplementing the Appraisal of Sustainability found that within the vicinity of Heathrow the current modelling tended to under-predict NOx concentrations to those recorded. Helen ApSimon acknowledged in oral evidence that “there were very many uncertainties” about air quality emissions and compliance and that “You can never be 100% sure in this field. Who would have predicted the Volkswagen scandal?”
The ENR scheme impacts on compliance with limit values in all 2017 Plan scenarios, for opening between 2026 and 2030, irrespective of the implementation of Government 2017 Plan actions and irrespective of the level of uncertainty applied to the PCM model projections. The reanalysis concluded that the risk of impacting on compliance is very high for the ENR scheme.
Air quality in the Gatwick area is already within legal limits and the latest analysis concluded that Gatwick was at “low risk of impacting on the UK compliance with limit values.” Additionally, it has “low vulnerability to uncertainties associated with the projection of future pollution concentrations and to the rate of growth in demand from a 2025 opening year.”
The latest figures from the air quality reanalysis show that there are 47,063 properties where annual mean NO2 concentrations are predicted to be higher with the NWR scheme (on average by 0.9 μg/m3), with 121,377 people affected. These figures only apply to the “Principal Study Area”, which includes the proposed airport site and a 2km perimeter (figure below). This perimeter was based on expert advice to the Airports Commission, and reflects the dispersal of NOx emissions. It is the area that is directly affected by the airport itself. Impacts beyond that area would, according to the Secretary of State, be “non-existent or minimal”. HAL said that the extent of their airports impact on the local population was limited, and pollution from background sources and emissions from non-Heathrow-related road traffic are the most significant contributors to air quality around the Heathrow.
We received evidence to indicate the traffic impacts from an expanded Heathrow extend beyond this 2km radius (see ‘Wider Study Area’ below). While airport related traffic might have a small absolute impact in terms of emissions, additional traffic on an already congested network can have a disproportionate impact in terms of creating additional congestion and additional pollution from non-airport related traffic. The air quality reanalysis found that “modelled roadside pollutant concentrations in Greater London are elevated across a wide area” this was because of the growth in additional vehicle trips generated by the airport. To only model population impacts within a 2km area seems to be an overly rigid view of the potential population impact.
Figure 38: Heathrow Airport–Air Quality Principal Study Area (Left) and Wider Study Area (Right)
It should be noted the air quality local population impacts have not been updated since they were estimated by the Airports Commission. They do not account for the latest uplift in demand forecasts and ATMs and surface access movements that would be realised with an expanded NWR and the consequent increase in pollution this would cause. It should also be noted that the population analysis is based on a static number of residents rather than an analysis including the population moving through the area.
Road traffic is the dominant emission source causing poor local air quality near Heathrow, as it is in general across the UK. The Government expects a mitigation package to be put in place by HAL to ensure that wherever possible significant effects are avoided, reduced or offset (“scheme level mitigations”). The Government, as part of the 2017 Plan, has outlined a range of wider initiatives to address the air quality problems associated with road traffic (“wider mitigations”). As discussed, legal compliance is primarily dependent on the timing of the introduction of, and effectiveness of, actions in the Government’s 2017 Plan to reduce emissions from vehicles on the wider road network, together with effective Real-Driving Emissions legislation; rather than scheme-level mitigations.
Some of the additional mitigation measures proposed by either the Heathrow or the Commission, include:
According to the latest reanalysis, “these mitigation measures have the potential, to varying degrees, to reduce overall emissions of air pollutants with the schemes and to reduce the impacts of those emissions on pollutant concentrations” for a NWR by between 2.4 and 3.6μg/m3 in 2030.
Reductions in overall risk is primarily reliant on the reduction in emissions from vehicles on the public highway. Thus, the principal driver for reducing adverse air quality impacts will be the actions in the Government’s 2017 Plan, to be undertaken at local, regional and national levels. Relevant actions identified prior to but included in the 2017 Plan are:
The additional actions proposed in the 2017 Plan include:
Cait Hewitt of the Aviation Environment Federation was confident that there will be some improvement in air quality because of these measures, particularly for the critical period of compliance for Heathrow in the mid-2020s. She said it was more a question of whether “we will have made sufficient progress to allow headroom below legal limit values to allow for the additional emissions associated with Heathrow expansion.” The air quality reanalysis, with reference to the latest Euro 6 vehicles and the impacts of existing RDE legislation (and the introduction of zero-emission vehicles), suggested that “that it is possible to be confident that roadside NO2 concentrations will fall in the future.” It similarly found that it is “the rate of decrease that is in question and the point in the future at which the downward trend is established.”
The air quality reanalysis work concludes that “the ability of measures presented in the [Air Quality] Plan to tackle poor air quality is open to challenge.” Scepticism was raised in evidence as to whether these mitigations would accelerate air quality improvements quickly enough for Heathrow’s compliance. Cait Hewitt said this scepticism was driven by the “very wide margin of uncertainty” and the fact that:
… the Government would need to be focused and very driven in terms of delivering some of these measures. They would need to be so effective that they created extra headroom to allow for the extra emissions from Heathrow. It leaves us in significant doubt that it can all come together in time for the runway opening as planned.
Reflecting on previous history of air quality compliance, Cait Hewitt commented:
It is worth remembering that 10 years ago, when Heathrow expansion was on the table, the Government’s modelling of the day said that everything would be fine by now; the runway could go ahead and there would be headroom within the limits. It turned out that we had been over-optimistic about the extent to which regulation, particularly around diesel vehicles, would be effective in bringing down air pollution.
The Mayor of London is adamant that “an expanded Heathrow can only hope to avoid breaking legal limits by relying on the air quality schemes we are introducing in London.” He added that he had “taken tough decisions to bring improved air quality and associated public health benefits [to Londoners], but these benefits will be lost to enable a third runway.”
The monetisation of air quality, as part of the economic appraisal, attempts to capture both the health and environmental damage costs from worse air quality. This is because NOx concentrations have potential impacts on sensitive ecosystems, whilst NO2 is important in terms of potential impacts on human health. Sensitive ecosystems may also be affected by nitrogen deposition, which is directly related to concentrations of NO2.
Jacobs, on behalf of the Airports Commission, used the damage cost approach to calculate the overall damage costs in accordance with the cost per unit mass values (in £/tonne) specified by Defra. Using this approach, the air quality damage cost estimated by Jacobs was £958 million, with the damage cost from NOx emissions at £94.2 million. The damage cost per tonne applied by Jacobs in the central estimate was £1,037/tonne which was sourced from the February 2011 Defra guidance and were uplifted to 2014 prices using a GDP deflator. However, as explained by Professor ApSimon, the Defra damage cost per ton of £1037 of NOx only applied to the long range secondary particle part of this and excluded the direct local NO2 effects - hence giving a small value for the damage costs of the NOx emissions compared with the primary particulate PM10 emissions. This was because at the time Defra had not determined how to quantify the health risks of the local exposure to NO2. Professor ApSimon concluded that the total damage costs estimated by Jacobs was an underestimate because of the exclusion of direct local impacts.
Defra’s guidance recognises that a full impact pathway approach is preferred if the resulting damage costs are greater than £50 million. The damage cost approach was preferred over the impact pathway approach by Jacobs due to the level of detail available on future pollution concentrations and the difficulty predicting mortality rates of the relevant populations from 2030 to 2050 and beyond. Jacobs elaborated, in Annex G of the local assessment, that monetisation of health impacts—discrete from those that dominate the damage cost assessment–was, therefore, limited to a 2030 snapshot of morbidity impacts through the increase in respiratory and cardiovascular related hospital admissions. It was only a “partial assessment of one component of health costs” (see box for details).
The Defra damage cost guidance was updated in September 2015. The damage cost, relevant to the Heathrow schemes, appears to be considerably higher than the previous guidance and are broken down by industry and location. In the latest guidance, the damage cost for NOx emissions relevant to the Heathrow expansion scheme (i.e. Transport outer London) are £64,605/tonne (in 2015 prices). Adjusting for inflation, this damage cost is around 63 times higher than that used by the Airports Commission. This higher damage cost reflects recent evidence published by the World Health Organisation that has strengthened the connection between exposure to NO2 and health impacts, including chronic effects. Other evidence supporting the health impacts associated with of exposure to NO2 concentrations is outlined by Defra in their September 2015 guidance.
Partial Impact Pathway Approach by Jacobs
In the Jacobs sensitivity analysis, it is the health impact of changes in NO2 and PM10 concentrations that were monetised, using the concentration-response coefficients provided in Defra’s guidance. These concentration-response coefficients capture the change in the number of hospital admissions from the baseline because of the change in concentrations of various pollutants and is used to quantify the effects of short term exposure. The evidence used to calculate the coefficient for nitrogen dioxide is, according to Jacobs, “considered less robust than those for the other pollutants. It is therefore suggested that the quantification of the effects of nitrogen dioxide are included for sensitivity analysis only, and that it is not used for central estimates.” These coefficients were applied to a spatial distribution of the projected 2030 population derived from CACI forecasts. These additional hospital admissions in 2030 were then valued using the Interdepartmental Group on Costs and Benefits recommended health values provided in Defra’s Impact Pathway guidance.
Applying the updated damage cost, the total damage costs from NOx emissions rises to around £5.9 billion, taking the total damage costs to around £6.8 billion (including PM10 costs). The revised damage cost was only applied to the long range secondary particle element estimated by Jacobs and excluded the direct local NO2 effects. Professor ApSimon acknowledged during oral evidence and follow-up correspondence that the updated Defra damage cost estimates are likely to be an overestimate but nevertheless should be higher. Professor ApSimon believed that the overestimation accounts for uncertainties about distinguishing effects of NO2 itself when combined with other pollutants—so called “double counting”. Professor ApSimon also noted that the dilution of airport emissions at ground level need to be considered and that it is important to distinguish airside emissions from traffic emissions associated with the airport. It is beyond the capabilities of the Committee to estimate the precise damage costs, but it should be higher than the previous Airport Commission estimates. Precise adjustments need to be made to the £5.9 billion estimate above based on the inclusion of direct local NO2 effects, to distinguish the effects of “double counting” and to adjust for dilution of airside emissions.
In the DfT’s updated October 2017 appraisal, the aggregate damage costs of air quality are now 90% lower at £30 million for NOx. It is difficult to see how this can be the case given the substantial rise in unit damage costs for NOx. The DfT states that the updated aggregate costs “reflects the use of the dispersion modelling in the revised approach, which better maps the relationship between emissions and concentrations, and so provides an improved approach to identifying impacts on affected populations.” The DfT said they are more confident using this approach given the updated guidance from on concentration response functions, which provided more assurance around the relationship between pollutants and health impacts. Using this approach, the DfT has valued concentrations directly which “will lead to much lower cost estimates of air pollution.” The DfT said that it used dispersion modelling that was used in the sensitivity analysis of the Jacobs report.The DfT compares the resulting costs using this approach to those produced by Jacobs on behalf of the Airports Commission. For Heathrow, the 2030 estimate is £3.8m, within the range of £1.4–£5.2m found by the Airports Commission.
According to Jacobs, if the impact pathway approach were to be formally adopted–as a substitute for the damage costs approach - “a full Impact Pathway Assessment would be required and further discussion with Defra would be expected.” Similarly, Professor ApSimon commented that “estimates of mapped concentrations and resulting exposure” would be required to apply the revised approach referred to by the DfT; and that “a proper assessment needs a specialised model like ADMS-Airports, which is the model we used for the Airports Commission work and which is currently being used by Heathrow”. Professor ApSimon subsequently concluded that “I have no idea how DfT can have calculated their value- it seems quite wrong!”.
The local assessment, including the detailed dispersion modelling, has not been updated since that produced by Jacobs in May 2015, with those results still directly referenced in the latest iteration of the Appraisal of Sustainability to support the NPS. In the Further Review and Sensitives Report, the DfT stated that it had updated the monetised costs “based on analysis commissioned by the department and Defra and undertaken by consultants Ricardo–AEA.” No such analysis had been commissioned.
In response to Committee scrutiny, the Secretary of State wrote to the Chair to clarify the Department’s approach to monetising the air quality costs. With the limited time available it has not been possible to fully scrutinise the Secretary of State’s explanation. At face value, it does not substantively clarify the points above. In particular, it is not clear how the Department relied solely on the sensitivity analysis in the Airports Commission appraisal when a full Impact Pathway Assessment would usually be required to estimate the damage costs using the impact pathway approach. Further, the Airports Commission sensitivity analysis only captures one component of the health costs and does not monetise the wider environmental costs from worse air quality.
544 For more information, see: Department of Environment Food and Rural Affairs (DEFRA), , September 2017
545 Royal College of Physicians, , February 2016
546 Council Directive
547 DEFRA, , February 2011
548 Council Directive , p 2
549 Mirocgrams per meter cubed.
550 Council Directive , p 16
551 For more information see: Air Quality in London, , House of Lords Library, 28 June 2017
552 DEFRA, , September 2017
553 Supreme Court Judgment, , 29 April 2015,  UKSC 28
554 DEFRA, , December 2015
555 DEFRA and Department for Transport, , May 2017
556 High Court Judgment, , 2 November 2016,  EWHC 2740 (Admin)
557 DEFRA and Department for Transport, , July 2017
558 ““, The Guardian, 21 February 2018
559 WSP, , Report No 62103867–041-03, October 2017
560 Department for Transport, Appendix A, A-8 Air Quality
561 This includes associated Pollution Climate Mapping (PCM) projections.
562 WSP, , Report No 62103867–041-03, October 2017, p 1
563 Department for Transport, , October 2017, p 49
564 Department for Transport, , October 2017, p 18
565 Heathrow Airport Limited ()
566 In the baseline projections, the Greater London zone is compliant by 2028 and the South East zone compliant before 2025.
567 WSP, , Report No 62103867–041-03, October 2017, p 4
568 WSP, , Report No 62103867–041-03, October 2017, p 4
570 WSP, , Report No 62103867–041-03, p 11
572 Department for Transport, , Appendix A, A-8 Air Quality, p 29
573 Department for Transport, , October 2017, p 49
574 WSP, , Report No 62103867–041-03, p 12
575 WSP, , Report No 62103867–041-03, p 29
578 Department for Transport, , Appendix A, A-8 Air Quality, p 29
579 Department for Transport, , Appendix A, A-8 Air Quality, p 14
580 Q495; Q537
583 Heathrow Airport Ltd ()
584 Heathrow Strategic Planning Group, March 2017 (); Q259
585 WSP, , Report No 62103867–041-03, p 28
586 Jacobs, , July 2015
587 Q494, Qq497-98
588 Department for Transport, , Appendix A, A-8 Air Quality, p 3
589 Real-Driving Emissions – EU legislation requiring vehicles to be subject to more stringent emissions testing procedures than at present, improving the real-world control of emissions.
590 WSP, , Report No 62103867–041-03, p 2
591 For more infotmation, see: Heathrow Airport Ltd, , January 2018
592 Department for Transport, , Appendix A, A-8 Air Quality, p 28
593 Department for Transport, , Appendix A, A-8 Air Quality, p 28
594 For more detail, see: DEFRA, , July 2017, p22-44
596 WSP, , Report No 62103867–041-03, p 37
597 WSP, , Report No 62103867–041-03, p 13
600 Mayor of London ()
601 Nitrogen dioxide also plays an important and independent role from PM2.5, in exacerbating asthma, bronchial symptoms, lung inflammation and reduced lung function, through short-term exposure.
602 Pollutant emissions are also associated with damage to built infrastructure and sensitive ecosystems. Nitrogen oxides (NOx) impacts on sensitive habitats and vegetation as it has the potential to alter nutrient availability and cause acid rain. NOx emissions are chemically transformed to NO2 in the atmosphere, which leads to increased nitrogen deposition which may affect sensitive ecosystems.
603 Jacobs, , May 2015
604 DEFRA, , February 2011
605 Correspondence from , 3 February 2018
606 DEFRA, , Updated September 2015
607 As noted by Professor Apsimon, DEFRA had not determined how to quantify the health risks of the local exposure to NO2
608 Jacobs, , May 2015,
609 DEFRA, , September 2015
610 World Health Organisation,, 2014
611 DEFRA, , September 2015, p 2; Professor ApSimon also commented that recent studies by WHO (the HRAPIE and REVIHAAP studies) had reviewed the epidemiological evidence and this had been used in studies for the European Environment Agency and others to estimate health impacts from NO2 exposure. Evidence provided by Mike Holland, an environmental economist, suggested that these additional health impacts could be a substantial addition for NOx emissions despite large uncertainties.
612 Q210; Correspondence from , 3 February 2018
613 Correspondence from , 3 February 2018
614 Department for Transport, , October 2017
615 Department for Transport, , October 2017
616 Department for Transport, Air Quality Monetisation – Explanatory Paper, February 2018
617 Department for Transport, Air Quality Monetisation – Explanatory Paper, February 2018
618 Department for Transport, Air Quality Monetisation – Explanatory Paper, February 2018
619 This figure is a single year taken from the estimate of impacts over the 60 year appraisal period as set out in the
620 Jacobs, , Appendix G, May 2015
621 Correspondence from , 3 February 2018
622 Jacobs, , May 2015
623 Department for Transport, Appendix A, A-8 Air Quality
624 Department for Transport, , October 2016
625 Correspondence from , 23 February 2018
Published: 23 March 2018