In particular, we are trying to understand the possibly conflicting information in ...
Effects of Air Pollution
In order to guide us in understanding the significance (or otherwise) of the readings from the St. Marys Lane sensor
we looked for the single figure that best represented the average, overall effect of the sort of pm2.5 and pm10 concentrations
we saw (i.e. pm2.5 values around 5 - 15 μg/m3).
We found estimates of the effects of air pollution on several individual medical conditions,
but fastened on long-term, all-age, all-cause, death rate, as being more generally applicable.
We hoped this could be used to understand and check...
community action or policy; and
individual decisions, such as whether to stay indoors on polluted days.
Since the smaller PM2.5 particle concentration was described as having the stronger correlation with all-cause, death rate,
and since we could find no mention of advantages of combining this with PM10 values,
we decided to base our figure on the PM2.5 values alone.
Since the St. Mary Lane sensor does not have NOx, O3 or other pollution sensors,
we thought it better to use the PM2.5 value to represent overall air pollution.
To do this, we concentrated on research which did not control for other air pollution variables, only for social, economic, geographical, and other non-air pollution variables.
Even then, we found that different studies implied
widely different effect sizes (see table 1.1). We eventually selected the 0.6% change in death rate for each 1μg/m3 of pm2.5 implied by the
UK Committee On the Medical Effects of Air Pollutants as being both UK specific and authoritative.
In comparing the above figure with that in the published studies, note that ...
- Some studies quote the effect of a larger, 10ug/m^3 change in pm2.5, which (since we assume linearity), should be divided by 10.
- Other studies quote the differences in death rates between co-cohorts having even larger differences in air pollution.
Confusingly, these are sometimes reported without specifying the difference in pm2.5 which is producing the effect.
- Still other studies report the effect of pm2.5 on specific diseases.
Apart from the very common cardiovascular diseases, these can be lower, or very much higher without affecting the all-cause death rate given here.
- The long-term effect is also very different from the short-term effect of changes in pm2.5,
which are better estimated by "time-series studies" of, for instance, pollution peaks.
In support of this effect size, we quote ...
This curve shows a (normalised) death rate varying with the average PM2.5 level in μg/m3 shown along the bottom.
Our straight line shows our simplifying assumption.
It could be argued that our assumed linear relation overestimates the effect of changes in PM2.5 in low pollution areas.
However, this may not be wise.
Firstly, some studies have failed to find a safe threshold for PM2.5,
and actually show more sensitivity at low pollution levels, with the effect of PM2.5 leveling off at higher levels.
Secondly, because particulate levels which are not great enough to kill could nevertheless have extremely deleterious effects on quality of life.
Examples of Pollution Reduction
- Over an average
year life span,
the 0.6% reduction in death rate associated with a 1μg/m3 reduction in pm2.5
would result in an increase in life span of 81.1 * 0.6% = 0.49 years or about 6 months.
If, as seems likely, improvements in air pollution improve health as well as death, this could be an extra half-year of good health.
To see the implications of this for the appropriately 7,000 residents of Ecclesfield Village,
we considered the effect of a village-wide 1μg/m3 reduction in PM2.5.
Assuming that the UK average death rate of around 1% per year applies to Ecclesfield,
this would reduce the expected 7000 * 1% = 70 by 70 * 0.6% = 0.42 deaths/year.
If this could be maintained over an 80 year lifetime, then it could give the average resident in the village half a years extra life.
However, the feasibility of any such reduction must be limited by the fact that only an
of UK PM2.5 originates in the UK, the rest originating from Continental Europe and elsewhere.
Something of this can be seen from the average PM2.5 map on the right.
To see what progress has already been made, we looked at the UK between 1970 and 2010,
and found that regulation and technology improvements reduced
population average PM2.5 concentration
from about 16μg/m3 to about 7.5μg/m3.
This was said to have eliminated the cause of 6.62% of all deaths.
If this is right, then it seems to explain most of the
80.40 - 71.97 = 8.43 years of extra life expectancy
during this period.
Comparison with other harms
For UK 15 - 49 year olds in 2015,
in the list of (possibly avoidable)
threats to health,
air pollution comes behind...
Since only air pollution applies directly to babies, we think that this might be the most significant avoidable risk factor
at least after not placing them on their back to sleep, not breast feeding, co-sleeping, and avoiding second hand smoke.
It be might also continue to be very high in the list for children.
- high blood pressure,
- high body mass index,
- high total cholesterol,
- low whole grains, low fruit,
- high fasting plasma glucose,
- low vegetables,
- low physical activity,
- low nuts and seeds.
- air pollution,
To get an indication of how much public money is spent to save lives in other ways,
we looked at comments on the
UK National Institute for Health and Care Excellence,
and found that they approve treatments costing up to about £25,000 per year.
The equivalent expenditure to eliminate 1μg/m of PM2.5 is therefore £25,000 / 2 = £12,500.
We also compared the death rate due to air pollution with that from road accidents.
We found reports that road accidents cause 0.3% of all-age, all-cause deaths.
If this is true, then a reduction of pm2.5 of 0.5g/m3 would save as many people as eliminating all road accidents!
Some Sources of PM2.5
Salt water droplets and surface water pollution lifted into the air by high winds over the ocean (Which we guess are not as deleterious as the particles from combustion).
Pollution blown from Continental industrial areas by Northerly or Easterly winds.
We have seen figures which imply that 45% of the air pollution in the UK is from external sources.
Traffic (we have seen a 22.6% contribution from this quoted for UK).
Industry (we have seen 10.3% contribution from this quoted for UK).
Peaks, possibly caused by people walking past the sensor while vaping.
Note that once generated, any pollution may become trapped by temperature inversions - e.g. when warmer air lies over colder valleys, hidden from the sun.
Alternatively, air pollution may be rapidly diluted by high wind speeds.
Some Problems and Qualifications
In comparing study results and selecting the effect size above,
we have assumed that population sizes are constant and the relationship between death rate and pm2.5 is linear.
However, it is difficult to know what happens at levels of pollution below those generally experienced, and the effect size is likely to reduce at very high pollution levels.
Since more specific information (such as age) is normally available, such average effects do not really apply to any individual person.
Genetic effects, such as those described by
Christopher Carlsten or
Sharine Wittkopp (2015)
Since we have not looked for studies which controlled for other constituents of air pollution,
simply adding their effect to the effect of PM2.5 described here is likely to produce an overestimate of the net effect.
The all-age death rates we have seen say little or nothing about the period over which exposure has to occur to produce the observed health effects.
Periods mentioned varied from 10 years, to whole life averages.
It could easily be that the major part of the effect of pm2.5 exposure occurs from ages 0-6, or even prenatally
Although we are hoping that the effect on death rates due to different causes can be compared,
the levels of any disability related to those causes, may be very different, and could dominate any comparisons made.
Although PM2.5 appears from the references given here to be the component of air pollution best correlated with all-age, all-cause death rate,
since they are composed of different materials, and may have different types of surface, different PM2.5s from different sources may have widely different effects.
The biological action of particulates may be related to their surface area,
in which case, since the total area of all the smaller particles tends to be greater than that of the larger ones,
it is possible that the even smaller ultra-fine PM0.1 particles that are causing most of the harm, not the PM2.5s (Robert F. Phalen 2019).
Such particles can also penetrate cells more easily, even getting in to the mitochondria within cells
In spite of these reservations,
we still suggest that the pollution figures given on the pm10 measurement page
together with an assumed effect size of 1μg/m3
to 0.6% death rate is a useful measure of the importance of reducing PM2.5
in the general case where there is no more specific information.
Although we lack training in epidemiology or medicine, in writing the above, we tried to take account of arguments to the effect that there is no significant causal link between PM2.5
and death rate.
However, the objections we found did not seem strong enough to override what appeared to the the consensus.
Some of the objections seemed to centre on the actions which California has already taken to reduce air pollution.
Sadly, arguments seem inevitable in the softer sciences, and become prominent objections whenever large commercial interests are threatened.
The mere fact of these objections does not therefore add information or change our conclusion above.
We found the web site of one skeptic however, which
although it contained video and other emotional material
which might be capable of doing more damage to one's peace of mind than the PM2.5s themselves,
also contained material we could not find the full-text of elsewhere. Having provided this health-warning we therefore link to
Luftdaten is an "Open Data" project. Their historical data is therefore available for download, which can be done from
Click on the folder with required date to see the list of files for that day.
The St. Marys Lane data, seems to be stored in file *sds011_sensor_31702.csv.