The Air Quality — PM2.5 indicator shows the daily mean concentration of fine particulate matter with aerodynamic diameter less than 2.5 micrometres (PM2.5), expressed in micrograms per cubic metre (ug/m3). PM2.5 is the most hazardous fraction of atmospheric particulate matter: its small size allows it to penetrate deep into the respiratory tract, reach the alveoli, and enter the circulatory system.
Major PM2.5 sources include fossil fuel combustion, biomass burning, industrial processes, and secondary photochemical reactions in the atmosphere. Chronic exposure is associated with significant impacts on biodiversity, ecosystem health, and agricultural productivity. The WHO 2021 guidelines recommend an annual limit of 5 ug/m3 and a daily limit of 15 ug/m3.
This KPI is a sub-type of the parent Air Quality indicator. It provides the PM2.5-specific time series within the air quality monitoring framework, complementing PM10 and other pollutant variables.
Data come from the Open-Meteo Air Quality API (CAMS model). The variable used is PM2.5 concentration at ground level. For each day, the average of hourly values is calculated to produce a daily mean. Data are interpolated to the site's geographic position at approximately 11 km spatial resolution across Europe.
Formula: Daily mean PM2.5 = sum of hourly PM2.5 values / number of hours
Unit: micrograms per cubic metre (ug/m3).
| Source | Provider | Coverage | Resolution | Period |
|---|---|---|---|---|
| Open-Meteo Air Quality API (CAMS) | Open-Meteo / Copernicus CAMS | Global (Europe: 11 km) | ~11 km | 2013 — present |
Line chart. A time-series chart displaying daily air pollutant concentrations over a selected period, with PM2.5 as one of the selectable pollutant variables.
Purpose: Answers the question "What are the PM2.5 concentration levels at this site over time, and are there concerning peaks or trends?"
Description: The chart card is located in the Assessment Risks section under the E1 pollution topic. The header shows "Air quality" with an E1 badge and a pollutant selector that allows switching between PM10 (default) and other variables. A time granularity selector offers "Hourly" resolution. The chart area displays the concentration values as a continuous line over the selected date range. Below the chart, a summary bar shows the selected period (e.g., "1 January 2026 - 20 March 2026") and statistics: minimum, average, and maximum values for the period. An "Add data" button allows site editors to trigger data generation.
How it's calculated: The chart plots the daily mean PM2.5 concentration (ug/m3) derived from hourly Open-Meteo Air Quality API data. Each point represents the average of all hourly readings for that day. The minimum, average, and maximum statistics in the summary bar are computed across all daily values in the selected period.
Legend: The line color corresponds to the pollutant type selected. No A-E quality scale is applied directly to the line chart; instead, the 5-band color scale from the quality ranges provides interpretive context:
| Level | Range (ug/m3) | Color | Meaning |
|---|---|---|---|
| Good | 0 — 20 | ■ #00A67A | Low concentration; minimal health and ecological risk |
| Fair | 20 — 25 | ■ #00DF80 | Moderate concentration; within acceptable limits |
| Moderate | 25 — 50 | ■ #FFD21E | Elevated concentration; sensitive groups may be affected |
| Poor | 50 — 75 | ■ #FF8B16 | High concentration; health risk for general population |
| Very Poor | > 75 | ■ #FF367F | Very high concentration; serious health and ecosystem risk |
Interpretation example: If the chart shows daily values oscillating between 8 and 18 ug/m3 with an average of 12 ug/m3, the site has generally good air quality for PM2.5 — well below the WHO daily guideline of 15 ug/m3. A spike to 65 ug/m3 during a winter day would indicate a pollution episode, likely from heating or atmospheric stagnation, pushing the site into the "Poor" range.
Line chart. A time-series chart tracking the number of days on which PM concentrations exceed the WHO-recommended threshold, with separate tabs for PM10 and PM2.5.
Purpose: Answers the question "How many days has this site exceeded safe PM2.5 levels, and when did exceedances occur?"
Description: The chart card shows "Threshold exceedance PM" in the header with an E1 badge. Two selectable tabs — "PM10" and "PM2.5" — allow switching between particulate types. When the PM2.5 tab is active, the chart displays a daily exceedance indicator or cumulative count line over the selected period. The WHO threshold for PM2.5 is 15 ug/m3 (daily mean). Days exceeding this value are highlighted, providing a clear visual count of non-compliant days.
How it's calculated: For each day, the daily mean PM2.5 concentration is compared against the WHO 15 ug/m3 daily guideline. Days where the mean exceeds this threshold are counted. The chart visualises either the daily values relative to the threshold line or the cumulative number of exceedance days over time.
Interpretation example: If the PM2.5 tab shows 12 exceedance days out of 90 in the first quarter, approximately 13% of days exceeded the WHO daily limit — a signal that winter air quality episodes are a recurring concern at this site. Zero exceedance days would indicate consistently safe PM2.5 levels.
Assessment Sidebar Row. A grade row in the assessment sidebar showing the air quality assessment score under the E2 Pollution category.
Purpose: Provides a quick summary of the overall air quality grade for the site within the sidebar navigation.
Description: In the assessment sidebar, under the "E2 Pollution" category heading, the "Air quality" row displays a letter grade (Adv or A-E). This row represents the parent air_quality KPI, of which PM2.5 is a sub-component. Clicking the row navigates to the air quality detail section.
How it's calculated: The sidebar grade reflects the parent air_quality KPI score, which aggregates across pollutant sub-types including PM2.5, PM10, and others. The specific grading methodology is determined by the parent KPI's quality ranges applied to the combined air quality assessment.
Interpretation example: If the sidebar shows "Adv" (advisory) for Air quality, the score indicates that air quality data is available but may not yet have a definitive grade assigned, or additional data generation is needed.
World Health Organization (2021). "WHO global air quality guidelines: particulate matter (PM2.5 and PM10), ozone, nitrogen dioxide, sulfur dioxide and carbon monoxide". WHO, Geneva.
Burnett, R. et al. (2018). "Global estimates of mortality associated with long-term exposure to outdoor fine particulate matter". Proceedings of the National Academy of Sciences, 115(38), 9592-9597.
European Environment Agency. "European Air Quality Index". https://airindex.eea.europa.eu
Open-Meteo (2023). "Open-Meteo Air Quality API Documentation". https://open-meteo.com/en/docs/air-quality-api
See the Calculation Methodology section for the core computation. Additional processing details are documented here for expert users.
pm_threshold KPI counts daily exceedances against the WHO 15 ug/m3 daily guideline and is displayed in the "Threshold exceedance PM" chart.