Optical Characterization of Atmospheric Aerosols

Atmospheric aerosols—solid or liquid particles suspended in air—play a central role in Earth’s radiative balance, air quality and human health. Optical characterisation seeks to quantify how these particles scatter and absorb light across wavelengths, enabling improvements in climate modelling, pollution monitoring and remote-sensing retrievals. Techniques range from laboratory-based spectroscopy and single-particle trapping to ground-based and airborne remote sensing. Core objectives include deriving the complex refractive index, extinction and scattering efficiencies, size distributions and hygroscopic growth of aerosols. Advances in instrumentation, inversion algorithms and theoretical frameworks have yielded more accurate optical parameters, reducing uncertainties in aerosol radiative forcing estimates and enhancing the fidelity of atmospheric transport models. Furthermore, direct measurements of photokinetic processes within individual droplets inform our understanding of chemical ageing and feedbacks between aerosol composition and optical behaviour.

Research from Nature Portfolio

Recent studies have exploited photoacoustic detection on optically trapped single nanodroplets to achieve attolitre-level sensitivity in absorption measurements. By monitoring the acoustic signals generated when a laser pulse is absorbed, researchers have directly observed size-dependent electromagnetic nanofocusing within sub-micron droplets. This approach revealed that photolysis rates in small aerosols can be an order of magnitude faster than in larger counterparts, highlighting the significance of particle size in atmospheric photochemistry. The versatility of this method promises broad application to diverse aerosol types, offering quantitative photokinetic data essential for refining climate and air-quality models.

Optical Characterization of Atmospheric Aerosols publication trend

The graph below shows the total number of articles in optical characterization of atmospheric aerosols across all publications each year (not limited to Nature Index journals).

Technical terms

Complex refractive index: A parameter m = m_r + i m_i describing how light propagates and is absorbed by a particle; the real part governs scattering and the imaginary part governs absorption.

Single-scattering albedo: The ratio of scattered light to total extinguished light by a particle, indicating its relative scattering efficiency.

Photoacoustic spectroscopy: A technique where absorbed light is converted into sound waves within a particle, allowing highly sensitive measurement of light absorption.

Cavity ring-down spectroscopy: A laser-based method that measures the decay time of light in an optical cavity to determine aerosol extinction with high precision.

Micro-pulse lidar: A low-energy pulsed laser system used to profile aerosol backscatter and extinction in the lower atmosphere.

References

1. Inversion of Near-Surface Aerosol Equivalent Complex Refractive Index Based on Aethalometer, Micro-Pulse Lidar and Portable Optical Particle Profiler. Remote Sensing (2024).
2. Photoacoustics of single laser-trapped nanodroplets for the direct observation of nanofocusing in aerosol photokinetics. Nature Communications (2016).
3. Aerosol size distributions during the Atmospheric Tomography Mission (ATom): methods, uncertainties, and data products. Atmospheric Measurement Techniques (2019).
4. A complete parameterisation of the relative humidity and wavelength dependence of the refractive index of hygroscopic inorganic aerosol particles. Atmospheric Chemistry and Physics (2017).