Influence of meteorological factors and air pollutants on bacterial concentration across two urban areas of the Sistan region of Iran

This study assesses relationships between meteorological factors and air pollutants with ambient bacterial concentration. In the two main cities of Sistan, Zabol and Zahak, airborne bacteria concentration was monitored using the settle plate method inside and outside household environments during dusty days and nights in summer, autumn, and winter in 2022. As context for the study, it was determined that air quality index (AQI) values >100 on most sampling days in Zabol (51.9%) and Zahak (70.4%), with higher values in summer than autumn and winter. The lowest and highest bacterial concentrations in outdoor air were observed at AQI < 50 (good) and AQI > 300 (hazardous), respectively, in both cities. Bacterial concentration showed a decreasing trend from summer to winter, which coincided with a decreasing trend of air pollutant indices, wind speed, and temperature in addition to an increasing trend of relative humidity. Temperature, relative humidity, and atmospheric pressure had negative correlations, while wind speed and air pollutant indices (PM₁₀, PM_2.5 and AQI) showed positive correlations and wind direction had no correlation with bacterial concentrations. The factors best related to bacterial concentrations were air quality indices (PM₁₀, PM_2.5 and AQI) in both cities, with the highest levels driven by dust storms in Sistan.