The PM Threshold Exceedances KPI is an exceedance indicator that shows how many times in a month the daily average value of PM10 and PM2.5 exceeded the recommended daily thresholds from international guidelines. It does not provide the absolute concentration of particulate matter, but counts the critical days — those on which air quality was insufficient according to public health and ecosystem protection standards.
This KPI is closely linked to the Air Quality KPI: the reference thresholds displayed in the exceedance chart correspond to the limit values set in that KPI. This is a visualisation-only KPI — it does not have A–E quality grades. Its purpose is to provide a temporal representation of the frequency of exceedance events, complementary to the absolute concentration values provided by the Air Quality KPI.
Important: To generate PM Threshold data, the Air Quality KPI data must first be calculated and made available.
Data come from Open-Meteo Air Quality, which provides daily estimates of PM10 and PM2.5 at 11 km spatial resolution, available from 2013 to the present, derived from the Copernicus Atmosphere Monitoring Service (CAMS) air quality forecast models.
The calculation process involves the following steps:
Unit: number of days per month (days/month)
Note: The thresholds displayed in the chart come from the Air Quality KPI configuration and may vary depending on site settings. The platform also shows EU Directive 2008/50/EC limits (PM10: 40 ug/m3, PM2.5: 25 ug/m3) in certain views.
| Source | Provider | Coverage | Resolution | Period |
|---|---|---|---|---|
| Open-Meteo Air Quality (WRD_OPNAQ_99) | Open-Meteo / CAMS (Copernicus) | Global | 11 km | 2013 — present |
Line Chart. A monthly bar/line chart showing the number of days in each month where PM10 or PM2.5 concentrations exceeded the daily threshold limits.
Purpose: To reveal how frequently particulate matter exceeds safe limits across the year, identifying months with the worst air quality episodes.
Description: The X-axis shows months (Jan–Dec). The Y-axis shows the number of exceedance days (0 to 31). Two series are displayed: one for PM10 exceedances and one for PM2.5 exceedances, each represented as bars or data points. Horizontal dashed lines indicate the WHO 2021 daily thresholds (PM10: 45 ug/m3, PM2.5: 15 ug/m3). A month/year selector allows navigation across different time periods. The chart title reads "PM Threshold Exceedances" and a tooltip explains the methodology.
How it's calculated: For each day of the month, the daily mean concentration of PM10 and PM2.5 (from Open-Meteo Air Quality data) is compared against the respective WHO 2021 daily threshold. If the daily mean exceeds the threshold, that day is counted as an exceedance day. The total count of exceedance days per month is displayed for each pollutant.
Interpretation example: If the chart shows 12 exceedance days for PM2.5 in January and 3 in July, it means that winter months have significantly worse fine particulate pollution — likely due to heating emissions and thermal inversions trapping pollutants near the ground.
Line Chart. A daily-resolution chart showing threshold exceedance events for PM2.5 and PM10 concentrations across the selected time period.
Purpose: To pinpoint exact days when particulate matter exceeded safe limits, enabling correlation with specific weather events or local emission sources.
Description: The chart displays daily PM2.5 and PM10 values over time, with horizontal reference lines marking the EU Directive 2008/50/EC thresholds (PM2.5: 25 ug/m3, PM10: 40 ug/m3). Days exceeding the threshold are highlighted. The tooltip explains: "This chart shows the number of days on which PM2.5 and PM10 concentrations exceeded the limits set by EU Directive 2008/50/EC."
How it's calculated: Each day's mean PM10 and PM2.5 concentration is plotted. The EU regulatory thresholds (PM10: 40 ug/m3, PM2.5: 25 ug/m3) are shown as reference lines. Exceedance days are those where the daily mean exceeds the respective limit.
Interpretation example: If the daily chart shows a cluster of PM10 exceedances during a 5-day period in February, this may indicate a prolonged thermal inversion event or a nearby construction/agricultural activity generating coarse particulate pollution.
Line Chart. A yearly summary showing the annual average PM10 and PM2.5 concentrations as a percentage of the regulatory limits.
Purpose: To provide a long-term view of air quality trends, showing whether average particulate matter levels are approaching or exceeding annual regulatory limits.
Description: The chart displays the annual average PM10 and PM2.5 values expressed as a percentage of the regulatory limits (PM10: 40 ug/m3, PM2.5: 25 ug/m3). A 100% line indicates the regulatory limit — values above this line mean the annual average exceeds the legal threshold.
How it's calculated: The annual mean PM10 and PM2.5 concentrations are computed from all daily values in the calendar year. Each value is then expressed as a percentage of the respective EU Directive 2008/50/EC annual limit.
Interpretation example: If the annual average for PM2.5 shows 120% of the limit, it means the site's annual mean PM2.5 concentration exceeds the EU regulatory threshold by 20% — indicating a persistent air quality issue requiring attention.
Summary Dashboard. A compact summary card showing the total number of exceedance days, the average PM reading, and the trend direction for the selected period.
Purpose: To provide at-a-glance key metrics about particulate matter threshold exceedances without requiring chart analysis.
Description: The card displays three metrics: Threshold Exceedances (total days with exceedance of PM limits, in days), Average Reading (mean PM value in the selected period), and Trend (improving, stable, or worsening compared to the previous period).
How it's calculated: Threshold exceedances count the total number of days where daily PM10 or PM2.5 exceeded their respective WHO thresholds. The average reading is the arithmetic mean of all daily PM values. The trend compares the current period's exceedance count to the previous equivalent period.
Interpretation example: If the card shows "18 days" of threshold exceedances with a "Worsening" trend, air quality has deteriorated compared to the previous period — more days exceeded safe PM limits, suggesting increased pollution sources or unfavourable meteorological conditions.
See the Calculation Methodology section for the core computation. Additional processing details are documented here for expert users.