An article has appeared on the Auto Express website with the title
“Traffic is not a key contributor to air pollution, study finds”
And the summary…
Researchers reveal a 65 per cent reduction in traffic on Scottish roads during lockdown had no significant impact on air pollution.
Like many articles in the press on any number of topics, this should lead calm, rational people ask some obvious questions.
Media outlets don’t tend to lie. They merely tend to quote selective data to support a narrative.
The article doesn’t provide a link to the research. It’s common practice in journalism not to cite primary sources, which instantly arouses suspicion.
However, a Google search for some key words brought me to the page https://www.stir.ac.uk/news/2020/09/lockdown-did-not-reduce-most-harmful-type-of-air-pollution-in-scotland/
This in turn links to the research itself on the British Medical Journal website at https://oem.bmj.com/content/early/2020/09/06/oemed-2020-106659
We now how the same source material to reference, assuming the writer of the Auto Express article made it back that far. Why not just reference the source?
So, these are my thoughts, reading through the text.
Firstly, framing the extent of research is important. Is it localised? Can the conclusions be extrapolated to the wider world?
The abstract in any academic paper is helpful, as it gives us the key takeaway information from the research without delving further in.
So, from the stated objective, this study is confined to Scotland and is framed to nitrogen dioxide and fine particulate matter (FPM) in the months of March and April 2020.
That’s our starting point. Off the top of my head, I know that population density in Scotland is considerably lower than in England, so it’s likely that vehicle usage is considerably lower.
That’s not necessarily important, so long as we’re comparing like for like and not drawing conclusions based on one to the other. Let’s just check population densities.
statista.com reports a population density in 2019 in Scotland of 70 people per square kilometre (the lowest of the UK). England, in comparison, is 432 per square kilometre.
Population density is light in Scotland, ergo traffic density is logically lighter, although I can’t find definitive figures on that, and we can’t consider car ownership alone.
Methodology was to use reference points during the same 31 day period in 2017, 2018, 2019, and 2020, with mean values used and weather normalisation applied. Here’s the graph. Not convinced by the choice of colours.
My thoughts instantly turn to wondering where these reference points are. I wouldn’t expect a reference point in Skaw, Shetland to show a great variation between 2017 and 2020, whereas a point in central Glasgow might.
The study doesn’t reference the source data for these reference points directly, but does indicate that the data are publicly available on the internet.
So, a bit of Googling brings us to http://www.scottishairquality.scot, which in turn gives us a handy map of reference locations. Interestingly, most are in the more densely populated Scottish Lowlands.
Now, the results do point to “significantly lower” NO2 levels and the Auto Express article does report this too. The results also show that FPM was much lower in 2020 than 2019, but comments on the period in 2019 being an outlier, due to Saharan sand.
And indeed, the data do show little difference in FPM between 2017, 2018, and 2020, when we look at the graph referenced above.
Now, some of my fellow EV advocates may not like that, but they do indeed seem to suggest that outdoor FPM at the sample points in Scotland has declined minimally due to lockdown.
However, we’re not done. The study is careful and responsible in making certain disclaimers and framing the study with regard to Scotland. Except in one important respect:
It references a decline in motor vehicle use across the UK, not Scotland. What was the decline in motor vehicle use in Scotland? Do we know? Remember my earlier comment about comparing like for like?
The study also makes a rather odd jump to include a speculative notion that lockdown may have caused increased exposure to FPM in the domestic environment, on the basis that people spent more time indoors.
I’m not disputing for one moment the risks of exposure to FPM in an indoor environment from, for example, cooking and smoking (where those pollutants exist) and the study references other research in this regard.
But do we know that people confined themselves to the indoor environment any more than they normally would? Lockdown didn’t necessarily confine people to their four walls.
Anecdotally, I know of many who spent time outdoors for their own mental well-being, either alone or with close family. I myself observed a higher number of cyclists on the roads.
But, to cut to the chase, the study concludes that “the impact of reductions in motor vehicle journeys during COVID-19 lockdown restrictions may not have reduced ambient PM2.5 concentrations in some countries.”
PM2.5 = FPM
That word “may” is important. The study is referencing a sparsely populated country in a northern European country. It can not be extrapolated or generalised to the world at large.
So any generalisation by Auto Express or anyone else that “traffic is not a key contributor to air pollution” in the context of the wider world is invalid.
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