Wroclaw in the lead of the most polluted cities – is it deserved?
Wroclaw again at the top of the world rankings of air quality… Is it deserved? Yesterday evening, we again took our place on the podium. The IQAir website showed that in terms of air quality our city took the third place, ahead of e.g. Karachi in Pakistan. This was reported in one of yesterday’s (i.e. 2021-09-27) articles in Gazeta Wrocławska.
Is it justified? Can such a ranking be trusted?
We have already written here about the reliability of these rankings, today another approach…
To determine the place in the ranking for Wroclaw IQAir website uses three sensors – two from the CIEP network (urban background station on Korzeniowskiego, and traffic station on Wiśniowa) and one independent sensor, located in the Stabłowice housing estate. For comparison, in Lahore (first place in yesterday’s ranking) the site takes into account data from 20 sensors. On the other hand, Tashkent (second place in yesterday’s ranking) does not show any sensor (as of 2021-09-28, 9:00 a.m.) – how the ranking is determined for this city, unfortunately, we do not know… The closest cities to Tashkent with sensors are Shymkent and Khujand, each more than 60 km away.
Location of IQAir service measurement sites – Wroclaw
IQAir test sites in Lahore
Location of IQAir service measurement sites – surroundings of Tashkent
So we have a ranking based on different data, collected in different ways and with different accuracy. Using an image comparison from the medical field – the diagnosis can be made based on detailed examination, using multiple devices, based on simple “auscultation” and looking into the throat, or by online consultation… Can such diagnoses be compared? Judge for yourself…
Secondly, it would be worth asking about the representativeness of the data. As mentioned above, the data for Wrocław used by IQAir service comes from three sensors – two working within the Chief Inspectorate for Environmental Protection network and the third – probably private, located in Stabłowice. Data from CIEP sensors show that PM2.5 concentrations during last night were at the level of 40-50 µg/m3 https://powietrze.gios.gov.pl/pjp/current. This means moderate conditions according to Polish Air Quality Index. Similar (but slightly lower) concentrations were shown by 15 sensors working within our network https://airquality.uni.wroc.pl/, about which we wrote here. So why did the sensor from Stabłowice show concentrations high enough to drastically “boost” our ranking? Can the data from it be considered representative for the whole city, or for a single neighborhood, street, or yard? You should answer this question by yourself…
