Aerosol Optical Depth (550nm)

Aerosol Optical Depth at 550 nanometers (AOD 550) is the definitive quantitative measure of atmospheric clarity used by meteorologists and photographers worldwide to assess air quality and visibility conditions. AOD represents the integrated extinction of sunlight by aerosol particles throughout the entire atmospheric column above a location, measured specifically at 550nm where human vision peaks and most cameras achieve maximum sensitivity. Unlike visibility measurements which describe horizontal sight distance near the surface, AOD captures the total aerosol burden from ground level to the top of the atmosphere, providing a comprehensive clarity metric that directly correlates with photographic quality.

The measurement is dimensionless but highly meaningful: AOD 0.0-0.05 indicates pristine air with exceptional transparency found in remote oceanic or polar regions, producing maximum color saturation and contrast in landscape photography. AOD 0.05-0.10 represents clean continental air typical of post-frontal conditions, yielding excellent photographic clarity with vivid blues and crisp distant details. AOD 0.10-0.20 indicates light haze from urban pollution or natural aerosols, slightly reducing color saturation but often creating attractive atmospheric perspective in landscape compositions. AOD 0.20-0.40 produces obvious haze visible in photographs as whitened skies and softened distant features, significantly reducing image quality for landscape work but sometimes enhancing diffused light for certain portrait styles. AOD values exceeding 0.40 indicate heavy aerosol loading from wildfires, dust storms, or severe pollution, dramatically degrading visibility and creating milky skies unsuitable for most outdoor photography genres.

PhotoWeather integrates CAMS (Copernicus Atmosphere Monitoring Service) global aerosol forecasts providing AOD predictions up to 5 days ahead, broken down by aerosol type (dust, smoke, sea salt, sulfates) to help photographers understand not just how much haze exists but what's causing it. For astrophotographers, AOD values below 0.10 are critical for capturing faint deep-sky objects, while landscape photographers often seek AOD below 0.15 for maximum sharpness and color fidelity.