# A Regional Multi-Agent Air Monitoring Platform
## 3 State of the Air in Plovdiv
3. Formation of secondary aerosols: Humidity facilitates chemical reactions in the atmosphere that lead to the formation of secondary particles, increasing the total PM10. Figure 5: A chart showing the concentration of fine particulate matter for Plovdiv-Sahat Tepe. Figure 6: \(Cont.\)  
However, this relationship may not be linear. At very high humidity (>80-90%), e.g., during fog, PM10 concentrations can increase significantly. Conversely, at low humidity (<30%), particulate matter is drier and does not increase by condensation but may remain in the atmosphere for longer periods if precipitation is absent. The correlation between RH and PM10 depends on the specific pollution sources and local meteorological conditions. For example, in industrial areas or with high use of heating systems the correlation may be more pronounced. Air temperature, relative humidity, wind speed, and wind direction are key climatic parameters that determine the characteristics of a region's atmosphere. Modern automated weather stations provide continuous measurements of these parameters, providing data at short intervals (e.g., every 5 s) during the day. The climate in the Plovdiv region is transient-continental with moderate rainfall and prolonged summer droughts. The region is dominated by westerly and easterly winds with relatively low speed. The autumn-winter period (October 2022-March 2023) is characterized by insignificant rainfall. During this period, local heating systems are widely used as temperatures drop. In the domestic sector, mainly solid fuels (coal, wood, household waste) are used. Due to the large number of sources and the low quality of fuels, the concentration of controlled pollutants increases in this period. The specific meteorological conditions in the area also contribute to the high levels of fine particulate matter--a large number of days with calm weather (wind speeds below 1.5 m/s), temperature inversions (occurring  
Figure 6: A chart showing the daily average concentrations of PM10 and PM2.5 and temperature for 2022 and 2023. Figure 7: A chart showing the daily average concentrations of PM10 and humidity for 2022 and 2023.  
on about 81% of days in the year), and fogs along the Maritza River all lead to the retention and accumulation of pollutants. The analysis of the data (Figures 6 and 7) for the winter period shows that the values vary above the average daily and annual standards for the protection of human health, specified in [9; 10]. The comparison of the values during the winter season with those registered during the summer period leads to the conclusion that the levels of this pollutant are directly related to domestic heating (increased consumption of solid fuels for heating) and car traffic. In combination with unfavorable climatic conditions and characteristic topographic features that disrupt the dispersion of emitted pollutants, high concentrations are registered. These factors, combined with Plovdiv's specific topographical and climatic characteristics, hinder pollutant dispersion, leading to elevated concentrations of fine particulate matter. The urban landscape, featuring high-density construction and syenite hills, further amplifies pollution retention. Monitoring air quality in Plovdiv requires data integration from multiple sources, including the European Environment Agency and local sensor networks. A comprehensive approach is necessary to track pollution trends, detect anomalies, and assess environmental and public health impacts accurately. The current data from Plovdiv's sensor network, which captures real-time measurements every five seconds, reveals that particulate matter (PM2.5 and PM10) concentrations frequently exceed EU air quality standards, particularly in densely populated areas. Despite some improvements in 2024, persistent efforts are needed to maintain long-term reductions in pollution. Regular air quality monitoring is essential to mitigating health risks, improving control measures, and understanding the relationship between pollution and climatic factors.