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Economic damage from NO2 cut by 80%

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Government cuts NO2 damage costs by 80% on expert advice


Local Transport Today 01 September 2017

The Government has dramatically cut the monetised health benefits of reducing nitrogen dioxide concentrations following the new expert advice about the impact of NO2 on mortality (LTT 18 Aug).

The lower benefits are revealed in the technical report accompanying the Government’s new plan for tackling roadside nitrogen dioxide emissions (LTT04 Aug). Road traffic accounts for an estimated 78% of roadside nitrogen oxide emissions in the UK.

The technical report for the draft plan published earlier this year reported £3.6bn health benefits over ten years for a scenario in which charging Clean Air Zones (CAZs) were implemented in London and 26 other cities.

But the technical report accompanying the final plan reduces this benefit to just £620m – an 83% cut.

Former DfT chief scientist David Metz wrote to the Joint Air Quality Unit (JAQU),  a team of officials from the DfT and the Department for Environment, Food and Rural Affairs, to enquire why the benefits had been so dramatically reduced. 

JAQU told Metz: “As you have observed, the valuation of the health benefits has changed notably since the consultation and this is mainly related to updated guidance from COMEAP.”

In 2015 COMEAP, the Committee on the Medical Effects of Air Pollutants, advised that a central coefficient of 1.025 per 10μg/m3 NO2 be used in cost-benefit analysis to reflect associations between long-term concentrations of NO2 and all causes of mortality.  This means that for every 10μg/m3 increase or decrease in NO2  exposure, there was a 2.5 per cent increase or decrease in the risk of mortality. 

COMEAP revised its advice to Government this summer, recommending use of a central coefficient of 1.0092 per 10μg/m3 NO2. That is, for every 10μg/m3  increase or decrease in NO2 exposure, there would be only a 0.92 per cent increase or decrease in the risk of mortality. 

Said JAQU: “Reducing the direct mortality impacts associated with NO2 has fed through to reduced health benefits associated with the measures assessed.”

A number of other factors had contributed to the reduction in damage costs, it said, including the latest dispersion modelling that reflects better understanding about how NOx emissions from vehicles disperse.

Said JAQU: “Overall, the updated NOx damage costs for road transport are approximately 80% lower than those used at consultation. This splits into roughly 60-65% resulting from the revised COMEAP advice and the remaining circa 15-20% resulting from the other updates.”

The health benefits of the central CAZ scenario reported in the final technical report are just £400m – within a range of £2.8m to £2.4bn – because only 17 CAZs have been assumed. 

The technical report suggests the implementation of CAZs represent terrible value for money. The central net present value of the CAZ scenario is -£1.1bn over the period 2018-2030, within a range of -£1.8bn to +£1bn. 

The health benefits are outweighed by additional costs for road users who will have to purchase new vehicles, or forego trips because their vehicle is non-compliant. Owners of non-compliant vehicles will also see the value of their vehicle fall. 

Defra has played down the significance of the new calculations. “This net present value excludes a range of potential benefits that could not be quantified and is, therefore, likely to be an underestimate,” it says.

“There is evidence that improving air quality by reducing the emissions of air pollutants has a range of other positive outcomes that cannot currently be quantified and monetised.” These include cognitive decline, dementia, lower lung function, an increased risk of type 2 diabetes, and exacerbation of asthma. 

It adds: “Furthermore, the need to take action to deliver compliance [with the EUlimit values for NO2] in the shortest possible time does not diminish.”

But Metz suggested the thinking could change: “Current policy is driven by the need to avoid exceeding statutory limits for NO2 concentration laid down in an EU directive that applies uniformly to all regions, in which context the scale of health benefits from remedial measures is not relevant. 

“However, Britain is to leave the EU, which may open the possibility of regulation of air quality based on UK targets set to reflect the balance of benefits in relation to costs. A down-rating of health benefits would then be relevant, particularly given the expected reductions in pollutants from improved vehicle technology and from the introduction of electric propulsion. 

“Whether the Government would be willing to propose targets to reflect UK conditions remains to be seen – it may depend on the outcome of the Brexit negotiations and on a judgment about the politics of air pollution.”

NO2 impact on mortality lower than we thought, say experts


Local Transport Today, 18 August 2017

Nitrogen dioxide may be responsible for far fewer lost life years than previously thought, experts on the medical effects of air pollutants have advised the Government. 

The impact of NO2 on mortality was discussed at a meeting of health experts convened by the Department for the Environment, Food and Rural Affairs (Defra) in June. A summary of the discussion says: “New advice from the Committee on the Medical Effects of Air Pollutants (COMEAP) indicated a much lower impact of NO2 on mortality than had previously been suggested.” Mortality is measured by the number of life years lost.

The meeting summary adds: “[COMEAP] also indicated that there were new uncertainty ranges around this link. It was important to note, however, that the debate and evidence is still evolving...”

The meeting noted that the World Health Organisation (WHO) uses a significantly higher hazard ratio, though WHO recognised this as “more uncertain than some other pollutant health outcomes”. 

The Government last month published a new plan to bring roadside NO2 concentrations down to within the EU annual limit value within the shortest possible time (LTT04 Aug). Road traffic is the major contributor to NO2 and more than 20 local authorities have been ordered to prepare action plans that could feature charging certain types of vehicle for entering Clean Air Zones.    

COMEAPwrote to environment minister Thérèse Coffey last month with its revised advice on the mortality impacts of NO2. It said population-based studies, following people’s health over several years, show statistical associations between higher long-term average concentrations of ambient NO2 where people live and increased mortality risk. 

“It is likely that some of this effect is due to NO2 itself,” said COMEAP. “However, as other co-emitted pollutants, e.g. from traffic, are also high in the same places, these could also be responsible to some extent. In our view, the available evidence and methods do not allow us to make a reliable assessment of the size of the effect which is attributable to NO2 itself.”

It added: “The Committee has not been able to come to a consensus view on how the epidemiological associations between NO2 and mortality can be used to either predict the benefits of interventions to improve air quality or to estimate the current mortality burden imposed on the UK population by air pollution. 

“Some members are doubtful that the evidence is sufficient to allow a robust recommendation for quantification to be made. This is particularly the case for effects likely to be caused by NO2 itself. Others think it important to make an estimate of the possible mortality benefit from reducing NO2 concentrations. They note that to recommend against undertaking quantification would have the same consequence for policy development as assuming that there would be no mortality benefit, which they do not consider to be likely.” 

COMEAP’s new advice significantly reduces the estimated mortality associated with NO2 from advice it gave two years ago.

In July 2015 the committee advised Defra (the Department for Environment, Food and Rural Affairs) that a coefficient of 1.025 per 10μg/m3 NO2 be used as a central estimate in cost-benefit analysis to reflect associations between long-term average concentrations of NO2 and all causes of mortality. This means that for every 10μg/m3 increase or decrease in NO2 concentrations, there would be a 2.5% increase or decrease in mortality.  

COMEAP’s new letter recommends two ways of assessing the mortality effects of policy interventions. 

“For interventions that reduce all traffic-related air pollutants, use the statistical association obtained from population studies,” it said. “In this case, NO2 is regarded as acting as a marker for the effects of the traffic pollutant mixture overall, including NO2.” 

Using this approach, COMEAP has recommended a coefficient of 1.023 per 10μg/m3 – i.e. for every 10μg/m3 increase or decrease in pollutant concentrations there will be a 2.3 per cent increase or decrease in associated mortality. 

It added: “For interventions that primarily target emissions of NOx, use 25-55% of the statistical association obtained from population studies. This is, in our judgment, the likely extent to which this association represents effects causally related to NO2. This is more uncertain than assessing traffic pollutants as a mixture.” The midpoint of the range is 40%, which has a central adjusted coefficient of 1.0092 per 10μg/m3. 

Says Defra: “This means that for every 10μg/m3 increase or decrease in NO2 exposure there is predicted to be a 0.92 per cent increase or decrease in the risk of mortality.” This is much lower than  the 2.5% estimate in COMEAP’s 2015 advice.

The above figures relate to mortality but the Government emphasises that air pollution can also have effects on morbidity, including exacerbating asthma. 

“Studies show that long-term exposure to air pollution reduces life expectancy by increasing deaths from lung, heart, and circulatory conditions,” says Defra. “There is emerging evidence of possible links with a range of other adverse health effects including diabetes, cognitive decline and dementia, and effects on the unborn child.”

COMEAP’s new estimates are contained in the technical report accompanying last month’s plan to bring down roadside NO2 concentrations.

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