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It does not seem that the air pollution level is getting any lower in Paris during the current shutdown due to COVID-19.

Why is that?

There are fewer cars. Are they only a small part of Paris' air pollution?

Where is the pollution coming from?

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  • $\begingroup$ Air pollution is down, but it isn't zero. Why are uou are expecting perfection? $\endgroup$ – David Hammen Apr 18 at 21:25
  • $\begingroup$ Human civilization produces more pollutants than only through cars. Factories are still producing aerosols while building our everyday consumption products, and farming still releases gaseous pollutants every day. $\endgroup$ – AtmosphericPrisonEscape Apr 18 at 23:31
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    $\begingroup$ In "Air quality historical data" on your linked page, the PM2.5 for April looks lower than previous years. (I haven't done the math.) $\endgroup$ – Keith McClary Apr 19 at 4:11
  • $\begingroup$ The measurements seem to be wrong. Cars are still a major contributor to pollution, and if they are reduced then air-quality should improve even if it's only by a few percentage points. If this isn't what the measurements say then it's very likely that the measurements are wrong. $\endgroup$ – Software Engineer May 1 at 17:17
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There are fewer cars. Are they only a small part of Paris' air pollution?

Recent evolution of European standard on emissions for private vehicle means that the average car is polluting orders of magnitude less than the average gasoline-burning heater.

Even for a city plagued by the widespread use of huge, inefficent cars (New York), the heating systems (heat and hot water) may account for >40% of the emissions https://blogs.ei.columbia.edu/2019/01/15/heat-pumps-home-heating/

A couple of emissions pie-charts for PM10 and PM2.5 for Paris in 2012 (from the report Inventaire régional des émissions en Ile-de-France Année de référence 2012 - éléments synthétiques Edition mai 2016 )

enter image description here and enter image description here

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  • $\begingroup$ Are gasoline-burning heaters common in Paris? $\endgroup$ – gerrit Apr 26 at 21:31
  • $\begingroup$ @gerrit I don't think it is that common, since there is a lot of municipal heating plumbing and heating from geothermal/heat pump ... so it makes the possibility that there are a few, very old very polluting heaters from the 70s very high. $\endgroup$ – EarlGrey Apr 26 at 21:34
  • $\begingroup$ Did you really mean to say "gasoline", or did you mean "heating oil" or "natural gas" instead? $\endgroup$ – Spencer Apr 28 at 14:54
  • $\begingroup$ @Spencer yes, sorry, I was thinking about the german Gasöl/Heizöl, so heating oil. $\endgroup$ – EarlGrey Apr 28 at 15:10
  • $\begingroup$ Heating oil is essentially Diesel fuel; so it's not that far off, just unidiomatic. $\endgroup$ – Spencer Apr 28 at 15:12
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Your linked report contradicts this one reported on phys.org that suggests a huge increase in air-quality in Paris. This matches similar reports from the rest of the world that lockdown has improved air-quality. That I can easily find studies that contradict your reference makes me doubt the veracity of the information it is presenting (and the evidence in the articles I have referenced).

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Measuring air-quality is a relatively new discipline that is still rapidly developing (this, this, this), and many more). It is not likely that any individual measurement is actually accurate. In science, it is usually the case that consensus must be built over time, statistically, before anything is accepted as actually true. This suggests that before we believe a result we should confirm it. The lack of maturity in this field makes me doubt the veracity of the claims in your link, and the claims in my link too. In fact, our default position should be to doubt everything until there is a sufficient weight of evidence that gives us enough confidence to believe it.

3

Logically, if you reduce a major pollutant for a significant period of time it seems very likely that pollution will fall. If you observer something different from that you must be suspicious of your results and attempt to verify them through a different set of observations performed using different techniques. This argument also makes me doubt the veracity of the claims in your link (and again, in mine).

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Ultimately, there is little strong evidence from these testing organisations to come to a conclusion on whether air quality has improved or not. There is the logical argument however that suggests that it should have improved, so we should weigh our opinions with that. Given this, it seems more likely that air-quality has improved, and given a lack of scientific consensus we should lean towards a belief that it has improved, rather than stayed the same.

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  • $\begingroup$ Sorry the bullet points are so large! :) $\endgroup$ – Software Engineer May 1 at 20:05
  • $\begingroup$ Good points. But then the questions goes into "please exactly define pollution?". The phys.org mentioned that the report says "it [the report] noted, however, that the lockdown had not led to marked declines in so-called PM2.5 and PM10 particles, the smallest and most harmful air pollutants, which can penetrate deep into the lungs and even enter the bloodstream." $\endgroup$ – EarlGrey May 6 at 8:38
  • $\begingroup$ Hey EarlGrey, thanks for taking the time to respond to my post. I can't see that quote in the question (or its history). Your own answer shows that traffic is a (or the) major contributor to both of the pollutants you have graphs for (approx. 30% of each), so if you lower traffic by 50%, one would expect a drop in the total quantity of those pollutants by around 15% (ish). That should be easily detectable given that your charts are at a minimum resolution of 1%. Again, given no detection one has to question the measurement techniques and results. $\endgroup$ – Software Engineer May 7 at 16:06

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