Quantitative and qualitative assessment of atmospheric suspended particles in the Chaharshanbeh Suri festival (case study: Tehran city)

The metropolis of Tehran, due to its specific geographical location on the southern slopes of the Alborz Mountains and high population density along with human activities, has always faced the issue of air pollution. In this study, the impact of the ancient celebration of Chaharshanbeh Suri on the concentration and chemical composition of particulate matter in Tehran's air during March 2025 was investigated. Hourly data and mean particle concentrations were obtained from monitoring stations of the Department of Environment. Additionally, particle sampling was conducted using fiberglass filters and a sampler with a flow rate of 1.7 m3/min. The morphological and elemental characteristics of the particles were determined using Scanning Electron Microscopy. The results showed that the mean concentration of PM10 on March 14 (one day after the celebration) reached 102.38 µg/m3, which was an 87% increase compared to March 11 and more than double the daily standard limit (50 µg/m3). The concentration of PM2.5 on the same day reached 54.62 µg/m3, which was 56% higher than the permissible limit (35 µg/m3). PM2.5 pollution remained in the air for 72 hours. The PM2.5/PM10 ratio increased from 0.05 on normal days to 0.55 in the days following the celebration, indicating a higher contribution of finer and more hazardous particles. Chemical analysis of the particles showed that carbon (34.2%) and oxygen (48.5%) together comprised over 82% of the particle mass. The significant presence of P(1.2%), Cl(14.3%), and Ca(28.7%) confirms the primary role of fireworks,, and biomass in the pollution of the celebration night.