Aerosol Optical Properties and Humidity Effects
Summary
Aerosols—suspended particles in the atmosphere—interact with sunlight and exert a critical influence on climate, air quality and visibility. Their optical properties include scattering, absorption and extinction of radiation, determined by particle size, composition and refractive index. Humidity profoundly alters these properties through hygroscopic growth: water uptake causes particles to swell, increasing the scattering cross-section and shifting angular distribution of scattered light. This effect is commonly quantified by the scattering enhancement factor, f(RH), the ratio of light scattering at elevated relative humidity to dry conditions. Hygroscopicity, often expressed by the parameter κ, links chemical composition to water uptake. Changes in aerosol optical behaviour under ambient moisture conditions affect radiative forcing estimates, remote-sensing retrievals and predictions of cloud formation. A detailed understanding of humidity-induced optical adjustments is therefore essential for accurate climate modelling, assessment of air pollution impacts and the refinement of satellite and ground-based observation techniques.
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Aerosol Optical Properties and Humidity Effects publication trend
The graph below shows the total number of articles in aerosol optical properties and humidity effects across all publications each year (not limited to Nature Index journals).
Technical terms
Relative humidity (RH): The ratio of water vapour in air to the maximum possible at a given temperature, expressed as a percentage.
Scattering enhancement factor, f(RH): The ratio of aerosol light scattering coefficient at a specified RH to that under dry conditions, indicating hygroscopic growth effects.
Hygroscopicity parameter, κ: A dimensionless value that quantifies the ability of aerosol particles to take up water and swell under subsaturated conditions.
Nephelometer: An instrument that measures the intensity of light scattered by aerosol particles, often under controlled humidity to determine f(RH).
References
- Measurement report: The variation properties of aerosol hygroscopic growth related to chemical composition during new particle formation days in a coastal city of Southeast China. Atmospheric Chemistry and Physics (2025).
- A global view on the effect of water uptake on aerosol particle light scattering. Scientific Data (2019).
- Aerosol optical properties in the southeastern United States in summer – Part 1: Hygroscopic growth. Atmospheric Chemistry and Physics (2016).
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