Short-Period Variations in Microphysical Characteristics of Aerosol Nanoparticles in the Dry Steppe Zone of Southern Russia in Summer

Aerosol nanoparticles play an active role in heterogeneous processes which change the optical and physicochemical properties of the atmosphere and the state of ecosystems and climate. Aerosol generation conditions, its geographical and seasonal features affect the microphysical characteristics of ultrafine aerosol. The work considers the first results of summer field observations of the microphysical characteristics of ultrafine aerosol particles in the near-surface air layer in the dry steppe zone of southern Russia in 2021 and 2022. Taking into account the synoptic and meteorological conditions, the daily variations in the concentration and size distribution of ultrafine aerosols (nucleation and Aitken modes and a transient subfraction) are studied, as well as their short-term variability. The permanent presence of Aitken particles at any time of a day and under any meteorological conditions is ascertained. Minimal concentrations of nucleation particles and Aitken particles are detected at night and in the early morning. The nucleation particle generation rate is typically the highest in the morning hours, when photochemical processes are active; this causes the morning maxima of concentrations of nucleation and Aitken particles. The concentration of transient subfraction particles increases during the nighttime. The features of the short-period variability of ultrafine aerosols are studied taking into account the general dynamics of daily aerosol generation and subsequent particle growth in the atmosphere, as well as through comparison with observations in other regions of the world. The results can be used for the study of the atmospheric composition and in chemical transport models to clarify the contribution of aerosols to the direct and indirect radiative effect and to climate change processes.