The Air Quality -- Clear-Sky UV Index indicator shows the daily mean UV Index calculated under clear-sky conditions, i.e. without cloud cover. It represents the theoretical maximum UV radiation that would reach the surface in the absence of clouds, accounting only for attenuation by stratospheric ozone and aerosols.
The comparison between the UV Index (which includes cloud effects) and the Clear-Sky UV Index allows quantifying the protective effect of cloud cover. A ratio of UV Index to Clear-Sky UV Index close to 1 indicates predominantly clear skies; significantly lower values indicate strong cloud attenuation. This metric is useful for estimating the potential UV stress on vegetation and organisms under scenarios of reduced cloud cover predicted by climate models.
The scale is the same WHO/WMO standard used for the UV Index, ranging from 0 to 11+. Since it excludes cloud attenuation, the Clear-Sky UV Index is always greater than or equal to the actual UV Index for the same time and location.
Data come from the CAMS model (Copernicus Atmosphere Monitoring Service) via the Open-Meteo Air Quality API, with 11 km spatial resolution and hourly updates. Daily values are calculated as 24-hour averages. The unit is dimensionless (WHO scale 0--11+).
Data come from the Open-Meteo Air Quality API, based on the CAMS model (Copernicus Atmosphere Monitoring Service). The variable used is uv_index_clear_sky (UV Index under clear-sky conditions, without clouds).
The calculation process follows these steps:
Unit: Dimensionless (WHO UV Index scale 0--11+)
Formula: Daily Clear-Sky UV Index = mean of 24 hourly clear-sky values
| 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 showing the daily clear-sky UV Index over time, with colour-coded quality bands.
Purpose: To show the theoretical maximum UV radiation intensity at the site in the absence of cloud cover, enabling assessment of potential UV stress under clear-sky conditions and comparison with the actual UV Index to quantify cloud attenuation.
Description: The chart is titled "Air quality" with the Clear-Sky UV Index measurement type selected from a dropdown that also offers PM10, PM2.5, ozone, nitrogen dioxide, sulphur dioxide, carbon monoxide, UV Index, and other air quality variables. The X axis shows dates, and the Y axis shows the clear-sky UV Index value (dimensionless). The chart background is divided into colour bands corresponding to the 5-level quality scale. A resolution toggle allows switching between daily and hourly granularity. A date picker allows selecting a specific date or date range. Summary statistics (Minimum, Average, Maximum) are shown above the chart for the selected period.
How it's calculated: Each point represents the daily mean (or hourly value if hourly resolution is selected) of the clear-sky UV Index at the site's coordinates, retrieved from the CAMS model via the Open-Meteo API. The calculation considers only ozone absorption and aerosol loading, excluding cloud optical depth, to produce the theoretical maximum UV irradiance.
Legend: The chart uses a 5-band colour scale for clear-sky UV Index values:
| Band | Range | Color | Meaning |
|---|---|---|---|
| Good | 0 -- 2.5 | ■ #00A67A | Low theoretical UV; minimal risk even without cloud protection |
| Fair | 2.5 -- 5.5 | ■ #00DF80 | Moderate theoretical UV; clouds provide additional protection in practice |
| Moderate | 5.5 -- 7.5 | ■ #FFD21E | High theoretical UV; ecosystems rely on cloud cover for protection |
| Poor | 7.5 -- 10.5 | ■ #FF8B16 | Very high theoretical UV; clear-sky days pose significant ecological risk |
| Very Poor | 10.5 -- 45 | ■ #FF367F | Extreme theoretical UV; maximum possible UV stress on ecosystems |
Interpretation example:
If the chart shows a daily clear-sky UV Index of 9.2 in summer while the actual UV Index for the same day is 5.8, the cloud cover reduced UV exposure by approximately 37%. If the gap between clear-sky and actual UV Index narrows during a dry spell (both reaching 8+), the site loses its cloud protection and organisms face near-maximum UV stress.
Highlights Table Row. A row in the risk overview table within the Highlights section, showing the air quality status for the site based on clear-sky UV Index and other pollutant data.
Purpose: To provide a scannable summary of the site's air quality alongside other risk-category KPIs.
Description: The row appears in the "Risk" section of the overview table and is labelled "Air quality". It shows the current status or value for the site. The column shows "N/A" when data have not been generated yet for the site.
How it's calculated: The value reflects the air quality assessment based on clear-sky UV Index and other pollutant concentrations from the CAMS model, aggregated according to the platform's air quality scoring methodology.
Interpretation example:
If the "Air quality" row shows a green indicator, the site's UV levels (and other pollutants) are within healthy ranges. An orange or red indicator would signal that UV exposure or other pollutant concentrations are at concerning levels for the ecosystem.
WHO (2002). "Global Solar UV Index: A Practical Guide." WHO/SDE/OEH/02.2. World Health Organization, Geneva. https://www.who.int/publications/i/item/9241590076
Bais, A.F. et al. (2015). "Ozone depletion and climate change: impacts on UV radiation." Photochemical & Photobiological Sciences, 14, 19--52. https://doi.org/10.1039/c4pp90032d
Open-Meteo (2024). "Air Quality API Documentation." Available at: https://open-meteo.com/en/docs/air-quality-api
Copernicus Atmosphere Monitoring Service (CAMS). "UV index forecasting." ECMWF. https://atmosphere.copernicus.eu
McKenzie, R.L. et al. (2011). "Ozone depletion and climate change: impacts on UV radiation." Photochemical & Photobiological Sciences, 10(2), 182--198.
See the Calculation Methodology section for the core computation. Additional processing details are documented here for expert users.