Air at the Zerjav station

Measured by Slovenian Environment Agency. We take the values from the European Environment Agency (EEA) under the CC BY 4.0 licence.

Values marked provisional have not been fully checked by the network yet. The EEA publishes verified data for the previous year once a year, usually by the end of September.

An hourly value is the average of one hour. We show the end of the hour: the value to 18:00 was measured from 17:00 to 18:00.

A day runs from midnight to midnight local time.

We only show an average when at least three out of four hours in the period have a reading. The EU air quality directive requires this for daily averages, and we apply the same rule to longer periods. We compare an annual average with the EU limit only once 90 % of hours are measured, as the directive requires. For 12 months and for a year we ask for more: if less than 90 % of hours are measured, every full calendar month needs readings for at least half of its hours. Otherwise a whole season could be missing from the average, such as summer, when ozone is highest.

We do not call a difference of up to 10 % a change, nor one of up to 1 µg/m³ at low levels, because weather and measurement uncertainty alone cause differences that size.

When a station sends no reading, the EEA sometimes fills the hour with a model estimate. We draw those hours dashed and leave them out of every average.

The EU limits come from Directive 2008/50/EC. Here they serve as a yardstick for comparison. When more than a tenth of the days or hours are missing, the number of exceedances can only be higher, so we write “at least” in front of it.