## 2 Sampling and Analysis Methods  
In this article, we present the analysis results of the measurement data on the ground-level concentrations of sulfur dioxide, nitrogen dioxide, and nitrogen oxide in the urban (Irkutsk city) and rural (Listvyanka settlement) areas of the Southern Baikal region. The experimental data cover the period between January 2020 and December 2023. The Irkutsk station is located on a hill in the southwestern part of the city. The sampling was conducted at the Limnological Institute (LIN) SB RAS (52.248, 104.260, altitude 496 m a.s.l.) at an altitude of 12 m above ground level. At the Listvyanka station, measuring devices are installed on the top of a coastal hill, 1 km northeast of the Listvyanka settlement (51.847, 104.893, altitude 656 m a.s.l.). The difference in altitude between the station and the settlement is 205 m. Figure 1 shows the schematic map of the layout of the observation stations and the main stationary sources of air pollution in the Southern Baikal region. The location and number of coal-fired boiler facilities in the Central Ecological Zone of Lake Baikal are indicated according to [41].  
To measure the concentrations of sulfur dioxide (SO\({}_{2}\)) and nitrogen oxides (NO and NO\({}_{2}\)), chemiluminescence method-based SV-310 and Z-310 gas analyzers from OPTEK  
Figure 1: Layout of the Irkutsk (IRK) and Listvyanka (LSTV) monitoring stations and the main sources of air pollution in the study region.  
(St. Petersburg, Russia) were used. These devices were verified annually in the OPTEK laboratory (St. Petersburg, Russia). The permissible measurement error limit in the range from 0 to 2000 ug m\({}^{3}\) is \(\pm\)25%.  
The meteorological parameters (wind speed and direction, air temperature) were measured at the Listvyanka station using the Sokol M1 meteorological station (Kazan, Russia). The vertical temperature stratification of the atmosphere was examined using the MTP-5 meteorological temperature profiler (Central Aerological Observatory, Russia) and the atmospheric radiosonde data obtained at the Angarsk station (52.48; 103.85) are available on the University of Wyoming website ([[https://weather.uwyo.edu/upperair/sounding.html](https://weather.uwyo.edu/upperair/sounding.html)]([https://weather.uwyo.edu/upperair/sounding.html](https://weather.uwyo.edu/upperair/sounding.html)), (accessed on 4 July 2024)).  
The measured data were collected in real time using the LIN SB RAS server. For this purpose, a server with an installed database running PostgreSQL was organized, as well as a program that receives data from the stations via the Internet, performs primary processing, and records measurements in the database (DB). The DB structure allowed us, through SQL queries, to select data from gas analyzers either jointly or separately, with averaging and filtering. Network access to the DB allows the prompt provision of data to interested parties, including interested departments at the regional level. The freely distributed BI platform, Grafana, was used for the prompt access, analysis, and display of the measured data. The dashboard shows several analytical curves from the two monitoring stations grouped by gases (Figure 2). The left half depicts the data from the Irkutsk station and the right half represents the data from the Listvyanka station.