The Air Quality — Sulphur Dioxide indicator shows the daily mean concentration of sulphur dioxide (SO₂) in the air, expressed in micrograms per cubic metre (µg/m³). SO₂ is a gaseous pollutant produced by the combustion of sulphur-containing fossil fuels (coal, fuel oil) and industrial processes such as oil refining and metal smelting. Volcanic activity is also a significant natural source.
In the atmosphere, SO₂ is converted to sulphuric acid (H₂SO₄), contributing to acid rain that damages vegetation, acidifies soils and water bodies, and compromises aquatic and terrestrial biodiversity. High concentrations cause leaf necrosis, chlorosis, and reduced growth in plants, with particularly severe effects on lichens and mosses — bioindicator organisms for air quality.
This KPI is a sub-type of the Air Quality parent KPI. All air quality sub-types on the platform are sourced from the Open-Meteo Air Quality API (CAMS model, European Centre for Medium-Range Weather Forecasts). Data is retrieved as hourly time series and aggregated to daily means for display.
The daily mean value is computed from 24 hourly readings per day retrieved from the Open-Meteo Air Quality API (CAMS atmospheric model). The variable used is sulphur_dioxide — ground-level SO₂ concentration interpolated to the site's geographic coordinates.
Formula: Daily mean = mean of 24 hourly SO₂ readings for the measurement day
Unit: µg/m³ (micrograms per cubic metre).
Data Sources:
| Source | Provider | Coverage | Resolution | Period |
|---|---|---|---|---|
| Open-Meteo Air Quality (CAMS) (WRD_OPNAQ_99) | Open-Meteo / ECMWF | Global | 11 km | 2013–present |
Line Chart. A time-series chart showing the SO₂ concentration over the selected date range for the monitoring site.
Purpose: To track sulphur dioxide levels over time, identify pollution episodes from industrial or volcanic sources, and compare the site against its control area.
Description: The chart displays values as a continuous line with data points. The Y-axis shows SO₂ concentration in mol/m² (column density). The X-axis shows dates. A dropdown allows selecting the pollutant variable. Summary statistics (mean, minimum, maximum) for the selected period are displayed above the chart. Site (ROI) and control area (CA) values can be compared when both are available.
How it's calculated: Each value is the arithmetic mean of hourly readings retrieved from the Open-Meteo CAMS model for the site's geographic coordinates. Monthly aggregation shows mean, minimum, and maximum values.
Note: This indicator is inverted — lower values indicate better conditions.
Interpretation example: If the chart shows a mean SO₂ of 5 µg/m³ with a spike to 40 µg/m³ on a specific day, the spike likely indicates a nearby industrial emission event or volcanic plume transport — worth investigating in correlation with wind direction data.
Map Layer. An interactive map overlay showing the spatial distribution of SO₂ column density across the site and its surroundings.
Purpose: To visualise where SO₂ concentrations are highest within and around the monitored area, revealing spatial patterns tied to emission sources.
Description: The map displays a colour-coded raster layer over the site boundary. The layer represents SO₂ column density (mol/m²) from satellite-derived atmospheric composition data. Users can toggle between different atmospheric pollutant layers using the pollutant selector dropdown.
How it's calculated: The map layer is generated from CAMS model output, showing the total SO₂ column density for the selected date. The raster is clipped to the site boundary and its control area for visual comparison.
Note: This indicator is inverted — lower values indicate better conditions.
Interpretation example: If the map shows a gradient from green in rural areas to orange/red near an industrial zone, it confirms that the SO₂ source is localised and directional — useful for identifying the dominant pollution origin.
Gauge. A semicircular arc gauge displaying the site's air quality score based on the selected pollutant, with the SO₂ sub-type selectable from a dropdown.
Purpose: Provides a quick grade (A–E) for the site's sulphur dioxide levels compared to established quality thresholds.
Description: The gauge arc spans from the best grade (A) on the left to the worst (E) on the right. The current value and letter grade are displayed at the centre. Site (ROI) and control area (CA) scores are shown on separate arcs for comparison. A dropdown allows switching between air quality sub-pollutants. The unit is µg/m³.
How it's calculated: The daily mean SO₂ concentration is mapped to the five-band quality scale. The gauge position and colour reflect the corresponding grade.
Note: This indicator is inverted — lower values indicate better conditions.
Legend: Five-band quality scale for SO₂ concentration:
| Level | Range (µg/m³) | Color | Meaning |
|---|---|---|---|
| A (Good) | 0–200 | ■ #00A67A | Very low SO₂; clean air, no ecological risk from sulphur deposition |
| B (Fair) | 200–350 | ■ #00DF80 | Low SO₂; minor industrial or volcanic background signal |
| C (Moderate) | 350–500 | ■ #FFD21E | Elevated SO₂; potential for acid deposition affecting sensitive vegetation |
| D (Poor) | 500–750 | ■ #FF8B16 | High SO₂; significant risk of acid rain damage to vegetation and soils |
| E (Very Poor) | 750–1250 | ■ #FF367F | Very high SO₂; severe industrial/volcanic source, acute damage to lichens and mosses |
Interpretation example: If the gauge shows 280 µg/m³ (grade B, green), the SO₂ levels are low — typical of areas without major industrial sources. The site has minimal risk of acid deposition damage to vegetation.
| Source | Provider | Coverage | Resolution | Period |
|---|---|---|---|---|
| Open-Meteo Air Quality API (CAMS) | ECMWF / Copernicus | Global | ~11 km | 2013–present, hourly |
| Sentinel-5P TROPOMI | ESA / Copernicus | Global | ~1,113 m | 2018–present |
See the Calculation Methodology section for the core computation. Additional processing details are documented here for expert users.