Aerosol size distribution: One year of measurements and retrieval procedures comparison

Aerosol size distribution (ASD) is the most important physical characteristic of aerosols, which determines the extent of aerosol penetration into a human’s respiratory tract: how particles are inhaled and where they deposit within the respiratory system. Therefore, correct measurements of aerosol size distribution are essential for assessing their potential impact on human health. Also, information about ASD is important for many different scientific applications, including radiative transfer models, source identification, air quality monitoring, optical remote sensing, atmospheric correction procedures, aerosol-cloud interactions, environmental impact assessment and climate studies. The retrieval of ASD from a diverse range of optical observations can be accomplished using GRASP (Generalized Retrieval of Atmosphere and Surface Properties) [1]. This study focuses on employing in-situ nephelometer measurements for ASD retrieval through the GRASP technique. To ensure the accurate processing of nephelometer data by the GRASP technique, it is imperative to determine appropriate model settings. The primary objective of this work is to determine the optimal GRASP settings for harmonizing a one-year series of in-situ aerosol measurements. The significance of this research lies in the developing of a multi-instrumental approach aimed at determining a correct model configuration, applicable to aerosol scattering measurements under diverse meteorological conditions. In-situ one-year measurements were conducted at the suburban measurement site in Racibórz (50 °E, 18 °N), utilizing the Aurora 4000, Aerodynamic Particle Sizer (APS) and Scanning Mobility Particle Sizer (SMPS) spectrometers. The Aurora 4000 is an integrating nephelometer that can measure light scattering in a sample of ambient air at three wavelengths: 450, 525, and 635 nm in several angular sectors from 10° to 90° through to 170°. Aerosol scattering measurements in 17 different angular ranges served as input for the GRASP algorithm, which was employed to obtain the size distribution of fine and coarse aerosol modes separately. The GRASP retrievals of aerosol size distribution were subsequently compared to measurements taken by both APS and SMPS instruments. A one-year series of data allows for the comparison of relatively long time series and the testing of different settings of the software and its performance. Special attention was given to finding best model settings under different meteorological conditions. This work was supported by the National Science Centre under grant 2021/41/B/ST10/03660. [1] Moallemi, A., Modini, R. L., Lapyonok, T., Lopatin, A., Fuertes, D., Dubovik, O., Giaccari, P., and Gysel-Beer, M.: Information content and aerosol property retrieval potential for different types of in situ polar nephelometer data, Atmos. Meas. Tech., 15, 5619–5642, 2022. https://doi.org/10.5194/amt-15-5619-2022