Air quality guides
Modelled air quality vs station measurements
Models and monitoring stations describe air quality in different ways. A single city page can contain recent modelled values and an older station archive. Read the source and period beside each section.
Pollution Alert · Last updated:
An area estimate versus a point measurement
An atmospheric model calculates concentrations across a grid. A station uses instruments at a particular location. A busy roadside site can differ from a background station and from a model estimate. That difference does not necessarily indicate an error: location and spatial scale matter.
Where does current Pollution Alert data come from?
We obtain hourly CAMS model data through Open-Meteo. For a city we use a point corresponding to its location, not a sensor network covering every street. A model cannot tell you exactly what is outside your window. The displayed hour is the local time of the data. Page generation time and data time may differ.
What do the station archives contain?
The monthly archives come from earlier measurement datasets aggregated by the service, including data obtained through OpenAQ. We show the available pollutants, period and station identifier, with a station name where the dictionary supplies one. A blank cell means no value is available. We do not replace it with zero or treat an old archive as a current reading.
Can the series be joined into one trend?
Not without checking comparability. A jump between a station archive and a model series may reflect a change in source, location or averaging method. We therefore keep recent daily averages and historical monthly averages separate. A mean of available country points is not a population-weighted national average.
Understanding coverage and freshness
The city counter covers our directory. The data counter requires at least one available concentration; the fresh-data counter requires a local date of today or yesterday relative to page generation. This does not mean every pollutant or a complete 24 hours is available. Always check the date on the individual city card.