Analysis of Air Quality in Three Slovenian Municipalities During the New Year Holiday Period

Festive fireworks can substantially affect air quality by causing short-term increases in particulate matter (PM) concentrations. This study analysed spatial and temporal PM pollution patterns in three Slovenian municipalities—Novo mesto, Hrastnik, and Jesenice—during the 2025/2026 Christmas–New Year holiday period. Using descriptive statistics, threshold-based peak detection, temporal segmentation, Pearson correlation analysis, and normalized descriptive indicators, the study evaluated PM2.5, PM10, relative humidity, and CO2 levels from late December to mid-January. Results revealed pronounced short-term pollution episodes, with PM2.5 peaking at 109 µg/m3 in Novo mesto, 128 µg/m3 in Hrastnik, and 133 µg/m3 in Jesenice. Most peaks occurred during late-night and early-morning hours, although Jesenice showed a more dispersed peak pattern. Fine particles represented the dominant PM fraction, with mean PM2.5/PM10 ratios ranging from 0.91 to 0.93. Normalized indicators showed that Jesenice had the highest relative variability and peak-to-mean ratios despite the lowest average PM concentrations. These findings show that holiday-period air-quality assessment should consider not only average concentrations, but also short-term peak intensity, timing, and local pollution profiles.