Insights into new particle formation in a Siberian boreal forest from nanoparticle ranking analysis

Abstract

New particle formation (NPF) plays a critical role in atmospheric processes and climate dynamics. Its mechanisms and impacts remain poorly understood in remote regions like Siberia. In this study, we used the dataset from a long-term campaign (2019-2021) employing particle spectrometers (NAIS and DMPS) to investigate NPF at a boreal forest site in Western Siberia. So far, this is the longest dataset for statistics of Siberian NPF. We classified NPF events, calculated formation and growth rates, and performed nanoparticle ranking analysis. Similar to other boreal sites, spring is the most favorable period for NPF events in Siberia. We observed a seasonal variability in growth rates, with the higher values in summer and the lower values in winter. We showed that the results of the ranking analysis can be used to identify the days with high or low NPF event probability, similar to the previous results obtained on the dataset from a Finnish boreal forest (SMEAR II station). Nanoparticle ranking analysis introduces a new metric, ΔN2.5-5, which is the daily maximum concentration of particles in the 2.5-5 nm range with subtracted background concentration and is linked with both probability and intensity of NPF. In order to identify the factors influencing NPF in Siberia, we analyzed the correlations between ΔN2.5-5 and concentrations of trace gases, such as SO2, O3, NO, and NO2, as well as global solar radiation, temperature, relative humidity (RH), and wind speed. We investigated the dependence of particle formation rate (J3) on ΔN2.5-5, finding a strong positive correlation confirming the connection of ΔN2.5-5 with the probability and intensity of NPF. SO2, linked to anthropogenic pollution, played a significant role in spring when most of the NPF events were observed. Ozone correlated positively with ΔN2.5-5 in spring and summer, likely due to volatile organic compound oxidation. NOx showed seasonally variable effects, with NO positively influencing NPF in autumn and NO2 showing both positive and negative correlations depending on the season. Global solar radiation significantly enhanced NPF by driving photochemical reactions leading to sulfuric acid production. Temperature suppressed NPF in spring and summer, aligning with the SMEAR II findings. RH had a negative influence across seasons, while condensation sink suppressed NPF, particularly in winter when its values peaked. Sulfuric acid calculated via proxy, critical for nucleation and growth, was a key driver of NPF in winter, spring, and autumn. These findings provide a comprehensive understanding of NPF processes in Siberia and highlight the importance of long-term datasets for uncovering regional and seasonal patterns in aerosol formation and growth.