HazeWert

HazeWert is a meteorological index used to quantify the haziness of the lower atmosphere at a given location and time. It serves as a simple, comparative measure that can reflect changes in aerosol content, humidity, and air quality that influence light scattering and visibility.

The term combines haze with Wert, a German word for value, and has appeared in European meteorology literature as a practical indicator in urban air-quality assessments. It is not a single standardized metric; several research groups have proposed formulations tailored to their data and objectives.

A common approach defines HazeWert as the ratio of diffuse horizontal irradiance to global horizontal irradiance observed near solar noon, with possible adjustments for solar zenith angle. Other variants incorporate aerosol optical depth, particle concentration, or visibility thresholds. Across formulations, higher values indicate greater haziness, while lower values correspond to clearer conditions. Because definitions vary, direct comparisons require consistent calibration and context.

Measurements come from ground-based instruments such as sun photometers and pyranometers, and can also be inferred from satellite data proxies. HazeWert is used in solar energy forecasting, aviation and traffic planning, and public health communication to convey haziness alongside more conventional metrics like PM2.5 or AOD.

Limitations include sensitivity to solar geometry, local calibration, and the influence of humidity and surface conditions. It is typically interpreted in conjunction with visibility data, aerosol optical depth, and pollutant concentrations. See also: Aerosol Optical Depth, Visibility, Atmospheric optics.