The Air Quality — Aerosol Optical Depth (AOD) indicator shows the daily mean aerosol optical depth. AOD is a dimensionless measure of the total amount of aerosols in the atmospheric column between the surface and the top of the atmosphere.
High AOD values indicate hazy air with high concentrations of suspended particles (dust, wildfire smoke, industrial pollutants, sea spray). AOD directly influences the amount of solar radiation reaching the surface: high values reduce direct radiation ("global dimming" effect), altering photosynthesis, ecosystem energy balance, vegetation phenological cycles, and soil thermal regulation.
This KPI is a sub-type of the parent Air Quality 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.
Data come from the Open-Meteo Air Quality API (CAMS atmospheric model). The variable used is aerosol_optical_depth (AOD at 550 nm). For each day, the average of the 24 hourly values is calculated. Data are interpolated to the geographic coordinates of the monitored site.
Formula: Daily mean AOD = mean of 24 hourly AOD readings for the measurement day
Unit: dimensionless (scale 0–1).
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 AOD value over the selected date range for the monitoring site.
Purpose: To track aerosol optical depth over time, identify pollution episodes, dust events, or wildfire smoke transport, and compare the site against its control area.
Description: The chart is located within the Risks > Pollution > Air Quality section. A dropdown filter allows the user to select "Aerosol Optical Depth" from the list of available air quality measurement types. The X-axis shows dates and the Y-axis shows AOD values (dimensionless). Resolution tabs allow switching between daily and hourly views. 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 plotted value is the arithmetic mean of hourly AOD readings retrieved from the Open-Meteo CAMS model for the site's geographic coordinates. When hourly resolution is selected, the raw hourly values are shown instead.
Note: This indicator is inverted — lower values indicate better conditions.
Legend: The chart uses a 5-band colour scale to indicate AOD quality levels:
| Level | Range | Color | Meaning |
|---|---|---|---|
| Good | 0–0.34 | ■ #00A67A | Clear atmosphere, minimal aerosol loading |
| Fair | 0.34–0.51 | ■ #00DF80 | Slight haze, minor aerosol presence |
| Moderate | 0.51–0.68 | ■ #FFD21E | Noticeable haze, reduced solar radiation reaching vegetation |
| Poor | 0.68–0.85 | ■ #FF8B16 | Heavy aerosol loading, significant dimming of direct sunlight |
| Very Poor | 0.85–1 | ■ #FF367F | Very high turbidity, severe global dimming with acute ecological stress |
Interpretation example: If the chart shows a daily mean AOD of 0.15 (Good, green), the atmosphere is clear with minimal aerosol interference. A spike to 0.75 (Poor, orange) would indicate a significant dust transport event or wildfire smoke plume, reducing direct solar radiation and potentially affecting photosynthesis at the site.
Map Layer. An interactive map overlay showing the spatial distribution of aerosol optical depth across the site and its surroundings.
Purpose: To visualise where aerosol loading is highest within and around the monitored area, revealing spatial patterns tied to emission sources, dust transport corridors, or wildfire plumes.
Description: The map displays a colour-coded raster layer over the site boundary. The layer represents AOD values 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 aerosol optical depth 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 uniformly low AOD values (green) across the site but elevated values (orange) in a band to the south, this suggests a regional dust transport event from lower latitudes that has not yet fully reached the site — useful for anticipating incoming aerosol episodes.
Gauge. A semicircular arc gauge displaying the site's air quality score based on the selected pollutant, with the AOD sub-type selectable from a dropdown.
Purpose: Provides a quick grade (A–E) for the site's aerosol optical depth 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 dimensionless.
How it's calculated: The daily mean AOD value 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 aerosol optical depth:
| Level | Range | Color | Meaning |
|---|---|---|---|
| A (Good) | 0–0.34 | ■ #00A67A | Clear atmosphere; full solar radiation reaching the surface, no dimming effect on ecosystems |
| B (Fair) | 0.34–0.51 | ■ #00DF80 | Slight haze; minor reduction in direct sunlight, negligible ecological impact |
| C (Moderate) | 0.51–0.68 | ■ #FFD21E | Noticeable turbidity; measurable reduction in photosynthetically active radiation |
| D (Poor) | 0.68–0.85 | ■ #FF8B16 | Heavy aerosol loading; significant global dimming, stress on light-dependent organisms |
| E (Very Poor) | 0.85–1 | ■ #FF367F | Severely turbid atmosphere; acute dimming with disruption to photosynthesis and ecosystem energy balance |
Interpretation example: If the gauge shows 0.25 (grade A, green), the atmosphere above the site is clear with minimal aerosol interference — full solar radiation is reaching the surface, supporting normal photosynthesis and ecosystem function.
| Source | Provider | Coverage | Resolution | Period |
|---|---|---|---|---|
| See Calculation Methodology | Various | Global | Varies | Varies |
See the Calculation Methodology section for the core computation. Additional processing details are documented here for expert users.