Can bimodal aerosol size distribution be retrieved from AURORA4000 polar integrating nephelometer data?

Atmospheric aerosols are tiny liquid and solid particles suspended in the air. They can scatter and absorb electromagnetic radiation, thus affecting the Earth’s radiative balance and climate. Additionally, aerosols can influence air quality, leading to respiratory and cardiovascular health problems.

To acquire information about the space-time variability of atmospheric aerosols and their optical and microphysical properties, various techniques are employed. In situ methods are typically performed at ground level, while remote methods use light to determine optical aerosol parameters.

This study focuses on the polar integrating nephelometer Aurora 4000 (Chamberlain-Ward and Sharp, 2011), which measures aerosol light scattering at different angles ranging from 10° to 170° across three wavelengths: 450, 525, and 635 nm. The main objective is to conduct sensitivity studies of the nephelometer by simulating theoretical signals for varying sets of optical and microphysical aerosol parameters. Thus examining the influence of various particle distribution parameters on light scattering measured by the nephelometer.

To simulate the nephelometer signals, the an advanced and versatile retrieval algorithm is employed. The Generalized Retrieval of Atmosphere and Surface Properties (GRASP) software (Dubovik et al., 2014; Lopatin et al., 2021) represents a state-of-the-art approach to integrating multi-source remote aerosol data, capable of retrieving atmospheric properties based on active (LIDAR) and passive (sun-sky photometer) remote techniques, as well as ground-based nephelometers.

Statistical parameters of aerosol size distributions (ASD) are derived from measurement data recorded by a ground-based system of aerosol size spectrometers, which includes a mobility particle size spectrometer (MPSS) and an aerodynamic particle size spectrometer (APSS). This combination allows for the determination of particle sizes within 10 nm to 10 μm. The synergy of these two instruments enables the acquisition of high-quality and wide range aerosol size distribution spectra.

Chamberlain-Ward, Steve, and Felicity Sharp. "Advances in nephelometry through the Ecotech Aurora nephelometer." The Scientific World Journal 11.1 (2011): 2530-2535.

Dubovik, Oleg, et al. "GRASP: a versatile algorithm for characterizing the atmosphere." SPIE Newsroom 25.10.1117 (2014): 2-1201408.

Lopatin, Anton, et al. "Synergy processing of diverse ground-based remote sensing and in situ data using the GRASP algorithm: applications to radiometer, lidar and radiosonde observations." Atmospheric Measurement Techniques 14.3 (2021): 2575-2614.

This work is supported by the National Science Centre grant number 2021/41/B/ST10/03660.