Predicting Pollution Proves Problematic in Paris

The Paris Mayor wins the battle over ‘Alternate Traffic’ during pollution peaks. This most restrictive traffic measure will now be introduced if the city and the region agree. But forecasting pollution is proving to be a problem.

Also, strict new traffic restrictions during Madrid pollution spikes and, a quick look at Killary Harbour on Ireland’s Wild Atlantic Way.



Process simplified but pollution forecasts demonstrably inaccurate.

Paris fog, not smog. Photo @DriveEurope

Paris fog, not smog. Photo @DriveEurope

The pollution peak in Paris over the weekend reignited the row over when to introduce the most restrictive traffic measures.

It seems Paris Mayor Anne Hidalgo has prevailed. Ecology minister Segolene Royal finally agreed yesterday (Monday) to simplify the introduction of so-called ‘alternate traffic’ whereby only vehicles with odd then even number plates are allowed in the city on successive days.

‘If city hall and the region together ask for alternate traffic, it will be granted as I promised,’ said Royal on twitter.

Hidalgo actually wanted alternate traffic to be triggered automatically when pollution is forecast to rise above a certain level but she did acknowledge the minister was ‘going in the right direction’.

Be that as it may, forecasting pollution levels accurately is not an exact science as this latest episode demonstrates.

When monitoring organisation Airparif first raised the alarm late on Saturday morning (31 October) it said pollution stood at 79/100 having forecast 67/100 the day before.

Levels were expected to rise to 87/100 on Sunday but ultimately came in at 82/100.

On Monday, Airparif had anticipated 79/100 but it turned out to be 67/100. Only today (Tuesday) did the prediction turn out to be on the mark: 39/100 v 40/100.

It is also worth emphasising that this latest pollution episode occurred at the weekend when traffic is a third of typical weekday levels.

Alternate traffic has been used twice so far during Hidalgo’s time as mayor, in March 2014 and March 2015 (out of a total of three times in the past seventeen years). Both times it was called off after a day when pollution dipped unexpectedly. The measure has not previously applied to foreign registered vehicles.

Also, Madrid: with parking charges depending on CO2 emissions, and new no-car zones, we had thought of the Spanish capital as a poster boy for environmental measures but, according to Feargus O’Sullivan from CityLab today, Madrid is still regularly capped with ‘a dingy dome of dirty air’ in winter called La Boina (the beret) by locals. Strict new rules will attempt to tackle the problem, including an automatic speed limit cut if pollution exceeds a certain level for two hours. If the problem persists this would be followed by non-resident drivers being banned from parking in the city centre, then alternate traffic and finally, in the worst cases, the restrictions will be extended to the entire city.


Ireland’s Wild Atlantic Way: the glacial fjord at Killary Harbour is located at the heart of Connemara's famous rugged and dramatic landscape. More at

A scene from Ireland’s north-south, tip to toe Wild Atlantic Way: ‘The glacial fjord at Killary Harbour is located at the heart of Connemara’s famous rugged and dramatic landscape.’


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