Investigation of seasonal changes in suspended particle concentrations in apartments in Bor

This study presents the results of seasonal variation analyses of suspended particulate matter (PM10 and PM2.5) concentrations measured in 15 residential apartments in the city of Bor, Serbia, during the period from February to June 2025. Measurements were conducted over 45-day intervals during both the heating season (February-March) and the non-heating season (May-June). The average concentrations of PM10 and PM2.5 measured indoors were compared between these two periods. During the heating season, the mean PM10 and PM2.5 concentrations were 18.2 µg/m³ and 12.0 µg/m³, respectively, while in the non-heating season, they averaged 19.5 µg/m³ and 11.1 µg/m³. The average Pearson correlation coefficients between indoor and outdoor PM10 concentrations were 0.33 in the heating season and 0.27 in the non-heating season, showing no significant seasonal difference. Similarly, the average correlation coefficients for PM2.5 concentrations were 0.51 and 0.47, respectively. The results indicate that there were no substantial seasonal variations in indoor PM concentrations, suggesting that infiltration from outdoor air remains the dominant source of indoor particulate matter. Occasional short-term increases in PM levels were observed, primarily due to cooking or particle re-suspension during cleaning activities; however, none of the recorded indoor concentrations exceeded the prescribed daily limit values for PM10 and PM2.5.