based on variable time intervals

<div style='text-align: left; text-indent: -48px;'><p><font size='2'>          <span>The map shows annual mean concentrations of Particulate Matter (PM10) in Europe based on daily averages with at least 75% of valid measurements, in µg/m3 </span></font><br /><span style='overflow: auto;'><span><span style='overflow: auto;'><span><font size='2'>(source: EEA, AirBase v.8 &amp; AQ e-Reporting)</font></span></span></span></span></p><p><font size='2'>          </font><span style='overflow: auto;'><span><span style='overflow: auto;'><span><font size='2'></font></span></span></span></span><font size='2'>Thresholds used in the map for annual values [µg/m3]:</font></p></div><p></p> <p></p><p><font size='2'>≤ 20: (20 μg/m3, as set out in the WHO air quality guideline for PM10)</font></p><p><font size='2'>&gt; 20 ≤ 31: (31 μg/m3, a statistically derived level corresponding to the 24‑hour limit value, as set out in the Air Quality Directive, 2008/50/EC)</font></p><p><font size='2'>&gt; 31 ≤ 40: (40 μg/m3, limit value as set out in the Air Quality Directive, 2008/50/EC)</font></p><p><font size='2'>&gt; 40 ≤ 50<br /></font></p><p><font size='2'>&gt; 50</font></p><p><font size='2'>Source: </font><a href='http://www.eea.europa.eu/data-and-maps/data/airbase-the-european-air-quality-database-8' target='_blank' rel='nofollow ugc noopener noreferrer'>AirBase v.<span style='color: rgb(68, 68, 68);'><font size='2'>8</font></span></a><font size='2'> &amp; <a href='http://www.eea.europa.eu/data-and-maps/data/aqereporting' target='_blank' rel='nofollow ugc noopener noreferrer'>AQ e-Reporting</a></font></p><p><font size='2'>AirBase is the European air quality database maintained by the EEA through its European topic centre on Air pollution and Climate Change mitigation. It contains air quality monitoring data and information submitted by participating countries throughout Europe.<br /><br />The air quality database consists of a multi-annual time series of air quality measurement data and statistics for a number of air pollutants. It also contains meta-information on those monitoring networks involved, their stations and their measurements.<br /><br />The database covers geographically all EU Member States, the EEA member countries and some EEA collaborating countries. The EU Member States are bound under Decision 97/101/EC to engage in a reciprocal exchange of information (EoI) on ambient air quality. The EEA engages with its member and collaborating countries to collect the information foreseen by the EoI Decision because air pollution is a pan European issue and the EEA is the European body which produces assessments of air quality, covering the whole geographical area of Europe.</font></p>