Classification and frequency of bursts of nanoparticle formation in the atmosphere of the coastal zone of the Lake Baikal

The paper presents the classification and frequency statistics of nanoparticle formation bursts in the atmosphere of the southeastern coast of Lake Baikal at the Boyarsky research station of the IPMS SB RAS. Measurements of the concentration and size distribution of aerosol particles in the range from 5 nm to 1 μm were carried out using a DAS-2702M diffusion aerosol spectrometer. We analyzed 257 days of expeditionary observations at the Boyarsky research station for the warm period (April-September) 2020-2023. At present, it is difficult to record nucleation as such using modern methods, since the detection limit of aerosol particles of most condensation counters is 2-10 nm. To date, there is no single mathematical criterion or method for identifying nanoparticle formation burst events. Therefore, particle formation events are identified based on visual data analysis, as described in the work of Markku Kulmala [1]. This technique has been widely used in foreign and Russian studies.

According to the technique, we visually analyzed the complete aerosol size distribution for each day separately. If a predominance of a new type of nucleation mode particles (5-25 nm) that appeared in the nucleation mode is observed for several hours (at least 1 hour), and this mode shows clear signs of growth to sizes characteristic of the Aitken mode (25-100 nm), then the day can be classified as a nucleation burst event day. Days with a nanoparticle formation event were divided into four classes:

- Class 1. Days when the particle growth rate (GR) and the rate of their formation (Jnuc) can be determined with a high degree of reliability, the nucleation mode is clearly distinguishable by the observed evolution over several hours.

- Class 2. Class 2 events are characterized by nanoparticle formation similar to class 1, but slightly weaker, with signs of particle formation and further growth quite clearly visible, but continuing for a slightly shorter period than class 1.

- Class 3. Days when the determination of parameters (GR, Jnuc) was impossible or the accuracy of the results was questionable.

- Class 4. Days that cannot meet the criteria of classes 1-3 are classified as uncertain, and are characterized by the appearance of some particles in the nucleation process, but no clear signs of continued growth, or growth observed in a non-nucleation mode. In this class, it is difficult to determine whether a nucleation event actually occurred or not.

For comparison and analysis of the study of the causes leading to nucleation burst events, days during which no particle formation was observed are of interest. Such days are classified as non-nucleation cases (class 0) in the analysis. The data analysis showed that the greatest number of intensive processes of new particle generation (class 1) is observed in April and May, and is 41.2% and 15.6%, while the least is in July (4.8%) and September (4.2%). It was revealed that generation events occur throughout the entire observation period, and the total frequency of nanoparticle generation events (classes 1-3 in total) is about 58% of all measurement days.

1. Kulmala M., Petäjä T., Nieminen T., Sipilä M., Manninen H.E., Lehtipalo K., Dal Maso M., Aalto P.P., Junninen H., Paasonen P. & Riipinen I. 2012. Measurement of the nucleation of atmospheric aerosol particles. Nat. Protoc. 7(9): 1651–1667.