Dear Mr Agnew. I forwarded on your comment to Dr Stenton who has kindly provided this reply.

——-

I thank Mr Agnew for his interest in my article.

As I pointed out, pollutants are generally produced together and it is difficult to disentangle the health effects of one from another. Nitrogen dioxide is the most easily measured and so has the greatest amount of local data. That is not to say that effects associated with it are necessarily caused by it rather than by some other pollutant.

The McCreanor study of the consequences of walking down Oxford Street for asthmatics showed a substantial effect at everyday levels of exposure, at least for those in Central London. The authors don’t say how many nitrogen dioxide measurements they made – they merely give average values and ranges. I don’t doubt that they were attempting to obtain representative measures of exposure rather than peak values. They also measured PM10, PM2.5 and PM0.1. I quoted the nitrogen dioxide values as they are the most easily related to pollution levels measured locally.

It is true that scientific studies are subject to error and uncertainty. There does however come a point when the weight of evidence is sufficient to overcome doubts about any individual study. That point has long been passed in relation to the health effects of air pollution.

It is also true that not all air pollution arises from vehicle exhausts, and their contribution varies in time and place. Wood burning is an import source – but this is just another area in which public policy lags well behind the science.

I have no special access to local pollution data. Simple face masks probably offer no protection and might even increase exposures ( Liu. Thorax 2017).

Hi Prof,

I think you may be barking up the wrong tree with the basic sciences. As in smoking and lung cancer the link will be proven by epidemiology.

https://www.bmj.com/content/363/bmj.k4904

I read your essay entitled “The Dangers of Air Pollution” with interest but it has raised some questions and comments that I would like to put to you.
As a scientist you will appreciate that all experimental measurements are subject to error and interpretation. One has to be careful that people, who should know better (i.e. politicians), repeat figures without knowing their significance and use them in an inappropriate manner to support their own political aims.
Could you clarify what you mean by “nitrogen dioxide levels averaged 140 µg/m3”? Is this an average of the seasonal, daily peak values, or a daily average or a weekly average, an average over a specified time interval or a rolling time based average? In the field of toxicology the residence or exposure time as well as the pollutant concentration is of importance when considering the likelihood of death or injury. In this context peek values have little meaning as they may occur over such a small time interval that the exposure to a person is minimal and therefore the risk is also minimal.
Correct me if I am wrong but my understanding of the adverse effects of NOx is in the production of photochemical smog that is produced by the reaction of NOx with unburnt hydrocarbons in the presence of sunlight. The main harmful constituents of the smog are ozone (O3) and any particulate matter that is held in suspension. This was very common in cities such as San-Francisco, Tokyo and Athens in the 1970s and lead to the Environmental Protection Agency (EPA) introducing measures that have reduced vehicle emissions. We very rarely in Gosforth have the climatic conditions that lead to the formation of photochemical smog. The causal relationship between NO2 and respiratory problems has been difficult to establish as reported in a recent WHO publication (1) which concluded “Therefore, the interpretation of the short-term as well as long-term epidemiological studies is that these results are not primarily due to NO2 per se but to other unmeasured traffic related pollutants or to secondary pollutants, which have complex interrelationships with NO2. Potential pollutants for which NO2 might be an indicator include black smoke, organic and elemental carbon and ultrafine particles.”
A more recent report by the COMMITTEE ON THE MEDICAL EFFECTS OF AIR POLLUTANTS (COMEAP) (2) included the following: “Studies of long-term exposure to NO2 report associations with all-cause, respiratory and cardiovascular mortality, children’s respiratory symptoms and lung function. There are still uncertainties about causality, due to strong correlations with other pollutants meaning that NO2 may be an indicator for other pollutants. However, the mechanistic evidence, particularly on respiratory effects, and the weight of evidence for associations of short-term exposure with morbidity and mortality led REVIHAAP to conclude that these associations with long-term exposures to NO2 are suggestive of a causal relationship. The US EPA’s (2015) current draft conclusion is that there is likely to be a causal relationship for long-term exposure and respiratory effects but that the evidence for cardiovascular effects and total mortality is only suggestive but not sufficient to infer a causal relationship.”
The health case against vehicle produced particulate matter (pm10 and smaller) is well established as particles this small, if ingested, can become lodged in the lungs and be carried into the blood stream. These particles are made up of carbon and active radicles of unburnt hydrocarbons produced by incomplete combustion in vehicle engines. The hydrocarbons are probably carcinogenic. I doubt however that all the particles monitored in the PM count were of this type as particulate monitors that use light scattering are not able to identify the source of the particle. Non-vehicle sources of pms include skin, domestic wood and coal fires, organic plant matter and dust. It could be that the high reading of pms occurred on a day when a south wind was blowing dust from the town moor into Gosforth High Street. The level of the pms will vary throughout the day and will be subject to factors other than vehicle movements. A recent report in May 2018 by Roger Harrabin a BBC environment analyst stated that “Ministers want to halve the number of people exposed to high levels of pollution from fine particles, known as particulates, by 2025”. One of the most contentious proposals is to reduce pollution from wood burners, which, along with solid fuels, cause 38% of particulate pollution. But a source at the Department for Environment, Food and Rural Affairs (Defra) told the BBC there was no plan to ban existing stoves – or the burning of coal and open wood fires, which are far more polluting than wood burners. To put this into perspective a wood burning stove produces 6.7 gm/hr of particulates, a HGV 0.5 and a Diesel car 0.17 (source Air Quality Expert Group 2017)
The vehicle sourced particles are clearly to be avoided but the true level of these is not reflected in the measured pm concentration.
I obtained an assessment of the air quality in the Haymarket (NE17RU) on Monday morning 11.30 am, 26th November 2018 (https://www.bbc.co.uk/news/science-environment-44203396). The pollution rating was1out of 6. This rating means there is a low chance of average nitrogen dioxide levels exceeding the annual legal limit. This is the same as the average for Newcastle upon Tyne, which is 1 out of 6 (good). The air at the Haymarket is generally clean, although there may still be some high concentrations of NO2 located close to major roads. The results surprised me considering the number of bus movements there are in the Haymarket and nearby. NE31DH, Salters Road Gosforth, also had a rating of 1.
These single figures should be viewed very carefully before drawing any broad conclusions from them. If you have access to the Newcastle air pollution data it would be very helpful to the public if you could post on this web site the periods when the levels of NOx and pms are high enough to be avoided. (A study in London in the 1990s (3) showed that NO2 levels were highest at night due to gas phase oxidisation of NO to NO2 at low temperatures). This would then allow shoppers to make an informed decision when to visit Gosforth High Street. Also do you have any views on the wearing of masks by pedestrians and cyclists to reduce ingestion of pms as is common in Japan and China?

(1) WHO Regional Office for Europe, “Health Aspects of Air Pollution”, (2003), Chapter 7 Nitrogen dioxide.
(2) COMMITTEE ON THE MEDICAL EFFECTS OF AIR POLLUTANTS, “Statement on the Evidence for the Effects of Nitrogen Dioxide on Health’, (2015).
(3) J.S Bower, G.F.J Broughton, J.R Stedman, M.L Williams, “A winter NO2 Smog Episode in the U.K”. Atmospheric Environment, Volume 28, Issue 3, February 1994, Pages 461-475.

Best wishes

Brian Agnew

Hi Paul,

Thank you for your comment. Just for clarity, the first sentence is the title of the linked article.

I think this is the source of the 14% national average figure. https://laqm.defra.gov.uk/public-health/pm25.html It doesn’t give a figure for what the proportion from road transport would be at roadside but almost certainly it would be quite a bit higher. More usefully, actual monitoring is available at the Newcastle Urban Observatory http://uoweb1.ncl.ac.uk

Generally the Newcastle figures are less than the UK legal limit but they are at a level where, according to the study, there is a diabetes risk. If nothing else this adds to the case for re-evaluating the PM2.5 legal limits with a view to reducing from 25μg/m3 to 10μg/m3 (the WHO suggested limit) or even lower.

Frightening indeed but I would suggest not a new reason to worry, as air pollution and its effect on public health has been known for some time (London’s Great Stink of 1858, 1956 Clean Air Act), however it reinforces the argument again about doing something about it, whether nationally, tackling the sources or in certain localities. However please bear in mind the report does say the following “This study has several limitations. Our analyses neither considered the source of PM2·5 nor the chemical composition and toxic content of PM2·5, which might vary within and among countries;…”
As such the report reinforces the link between Air Pollution and (the onset of) Diabetes, and whilst (UK) PM2.5 nationally from road transport was around 14% in 2014, it is not the only source (which needs tackling). So maybe a slight correction on the first sentence above is required.

In A&E I see children’s terror as they choke from polluted air this summer
https://www.theguardian.com/healthcare-network/2018/jul/12/ae-children-terror-choke-polluted-air-london
12 July 2018

Child’s asthma death linked to illegal levels of air pollution
https://www.theguardian.com/environment/2018/jul/04/report-links-childs-asthma-death-to-illegal-levels-of-air-pollution
4 July 2018

UK schools banning school run to protect pupils from air pollution
https://www.theguardian.com/environment/2018/jul/13/uk-schools-move-to-ban-the-school-run-to-protect-pupils-from-air-pollution
13 July 2018

“This new study makes an even stronger case, suggesting that the current limits on air pollution in the United States might be too high. The EPA’s pollution threshold on particulate matter is 12 μg/m3, or micrograms per cubic meter of air, but this study says the risk of diabetes starts at about 2.4 μg/m3.”
For comparison, the UK limit for PM2.5 particulate matter is currently 25μg/m3.

https://www.theatlantic.com/health/archive/2018/07/a-frightening-new-reason-to-worry-about-air-pollution/564428/

Link to the related study published in The Lancet:
https://www.thelancet.com/journals/lanpla/article/PIIS2542-5196(18)30140-2/fulltext