Topic 34: The Great Dirty Diesel Scare

PARTICULATES

The media headline, that man-made particulates cause “29,000 premature deaths” in the UK is from a report, dated 2010, by the Committee on the Medical Effects of Air Pollutants, COMEAP.  The snazzy title is The Mortality Effects of Long-Term Exposure to Particulate Air Pollution in the United Kingdom, dated 2010.  The report runs to 98 pages. Paragraph 2 of the Executive summary provides:

• At sub-para (a): “The current (2008) burden of anthropogenic particulate matter air pollution is, with some simplifying assumptions, an effect on mortality in 2008 equivalent to nearly 29,000 deaths in the UK at typical ages and an associated loss of total population life of 340,000 life-years. The burden can also be represented as a loss of life expectancy from birth of approximately six months”.
• At sub-para (d): “The uncertainties in these estimates need to be recognised: they could vary from about a sixth to double the figures shown”.

However:

1. The meaning of and basis for “29,000 premature deaths at typical ages” is obscure.
2. Table 8.1 of the 2010 report provides a loss of life expectance ranging from three days, when the 340,000 life years allegedly lost are allocated to the UK population as a whole,  to 11.5 years, when the loss is allocated to the alleged 29,000 premature deaths.  The “Six months” was derived by dividing the 340,000 life years lost by the total deaths in the base year, 2008. That begs the question, if they do not know how to allocate the alleged 340,000 life-years lost how on earth did they estimate that the loss is indeed 340,000 life-years?  Further, the headline of “29,000 premature deaths” makes no sense.  After all air pollution must affect all our life spans to some degree so that all deaths are “premature”.
3. The range cited at the second bullet point above represents 75% plausibility limits.  Had the more usual 95% limits been used they would have embraced zero, meaning that, in statistical terms, the forecast shortening in life expectancy due to particulates is no different from zero.
4. The loss of life cited by COMEAP is that attributed to all man-made particulates. Figure 3.2, reproduced below, shows that only roughly 15% of particulates in inner London are from road traffic, 11% in outer London and 8% in the rest of England.  COMEAP told us that removing those particulates may increase average life-expectancy by approximately 16 days for England and approximately 41 days in Inner London. 

Furthermore, the computation and assumptions underlying the data are opaque.  The report refers to an earlier report with the title, “Long-Term Exposure to Air Pollution: Effect on Mortality”, published in 2009, 186 pages.  That report refers to “Relative Risk” coefficients derived from the American Cancer Society (ACS) study (Pope et al, 1995, 2002).  COMEAP uses those coefficients, together with other sources, to compute the changes in life expectancy.  However, the complexity and opacity of the whole undermines confidence.  Indeed common sense suggests that it may be nigh on impossible to isolate the effects of particulates from the other factors.

Additionally, many of the estimates and error ranges depend on “eliciting” the views of “experts”.  That process, known as elicitation, is heavily criticised by Professor P K Hopke in the 2009  COMEAP report, in Appendix 1 thinks policy should not rely on such a procedure: "In spite of its use both in this analysis and in the United States, I find the elicitation of experts to be an approach that involves too much subjectivity and is likely to be unreliable. I would suggest one be very careful using the guesses of experts as the basis of policy decisions"..

There is also a critique of the ACS study, and by implication of the risk coefficients used by COMEAP, by Joel Schwartz, Adjunct Scholar of the Competitive Enterprise Institute.  The executive summary, available here, makes compelling reading.  Schwartz points out that the ACS report contains the biologically improbable.  For example, “PM increased mortality in men, but not women; in those with no more than a high school degree, but not those with at least some college education; in former-smokers, but not current or never-smokers; and in those who said they were moderately active, but not those who said they were very active or sedentary.  Even more surprising, the ACS study reported that higher PM levels were not associated with an increased risk of mortality due to respiratory disease; a surprising finding, given that PM would be expected to exert its effects through the respiratory system”.   All that suggests that the ACS paper is deeply flawed and that, probably, particulates have no measurable effect on lifespan, a conclusion consistent with the COMEAP findings, where, at section 3.1.3, risk coefficients range from unity to 1.15.  A value of unity implies that particulates have no effect.

Worse still, if that is possible, the COMEAP REPORT, UK Plan for tackling roadside nitrogen dioxide concentrations, of July 2017 has, under the heading, Estimating the mortality burden attributable to current concentrations of air pollutants:

 “Some Members do not think it appropriate to try to calculate an overall burden of the mortality associated with the air pollution mixture. Others are of the view that an attempt can be made based on associations with NO2 and PM2.5, and using information from two-pollutant models. This could be presented as a range of central estimates, but methods to represent the full statistical uncertainty are unlikely to be available”.

We ask, why on earth would anyone want to found an expensive policy on such vague words?

Lastly the London Atmospheric Emissions Inventory (LAEI) of 2013 provides that roughly 50% of particulates and NOx are from road traffic, rather than the 8% to 15% apparent from COMEAP’s figure 3.2 in the 2010.report, The Mortality Effects of Long-Term Exposure to Particulate Air Pollution in the UK .

COMEAP data

PM_2.5 Tonnes per year London Atmospheric Emissions Inventory (Pivot Table 25).

With variations between studies on that scale can anyone believe any of it, particularly the scary death statistics leading to this overblown diesel bashing scare?

Top that off with the reports that most road based particulates are from brake and tyre wear, not the exhaust, and we have a neat proof that the attack on the diesel is overdone if not entirely misplaced, see Engineering  and Technology, March 2017. Also the Air Quality Expert Group's report, Non-exahust emissions from road traffic, dated 2019, provides the following figure. It shows that particulates from exhausts are rapidly becoming a minor component.

Conclude:

The data from COMEAP suggests trivial average life expectancy gains from banning all diesel vehicles.  The plausibility limits on those gains are extraordinarily wide. The basis for the numbers is opaque.  Probably the American ACS study, upon which the whole depends, is junk science. In truth particulates may very well have no discernible effect on lifespan whatsoever. 

The proportions of particulates attributed to road traffic are far higher in the London Atmospheric Emissions Inventory than in the COMEAP 2010 report thereby casting doubt on the reliability of both studies, let alone the matter that tyre and break wear may be the major source of particulates. Indeed the AQEG report, Non-exahust emissions from road traffic, dated 2019, shows that particulates from exhausts are rapidly becoming a minor component.

For those reasons the attack on the diesel appears to have little or no solid basis. Deaths from alcohol abuse or obesity (think chocolate biscuits) will almost certainly far outweigh the effects of atmospheric pollution.  Indeed the considerable costs imposed by the diesel-bashing scare may cause, rather than reduce deaths, by diverting scarce resources from far more important vectors.

NITROUS OXIDES, NOx

The COMEAP paper with the title ‘Considering the evidence for the effects of Nitrogen dioxide on health’, dated June 2014, is extraordinarily cautious.  For example at paragraph 38 we have:

“In 2008, the EPA considered the evidence suggestive but not sufficient to infer presence or absence of an association between short term exposure to NO2 and mortality. Now the evidence has increased and the EPA considered that there is likely to be a causal relationship”. 

The report as a whole suggests great uncertainty.  One senses that the Committee is being pushed to find evidence when none is available or where whatever is available is very weak.

We have not researched the whole in detail, but the impression formed from this report is that, although it would be extraordinary if pollutants had no effect on health and life span, the affects may be slight at the levels found in the UK, Europe or the United States, suggesting that, in those areas, the costs of reducing either particulates or NOx may far outweigh the benefits.

Embedded within the COMEAP report UK with the title, “ Plan for tackling roadside nitrogen dioxide concentrations Technical report” dated  July 2017 is a reduction in economic damage attributable to nitrites of 80%.  For discusion reported in Local Trasport today see http://www.transport-watch.co.uk/economic-damage-no2-cut-80

PDF: 

THE GREAT DIRTY DIESEL SCARE 07.pdf