Particulate Matter as a Carrier for Airborne Bacteria: An Integrated Assessment of Chemical and Microbiological Air Quality in Urban Nagpur, India

Vehicle emission-induced air pollution is a significant environmental and public health issue in rapidly urbanizing areas. This research assesses the correlation between major air contaminants (PM₂.₅, PM₁₀, NOx, and SO₂) and airborne microbial density across 32 urban sites in Nagpur, India. Airborne bacteria were sampled using the passive settle plate technique and analyzed for colony morphology, Gram staining, and hemolytic activity. Colony-forming units (CFU) varied between 0.68 ´103 and 10.35 ´103 CFU/m3 with higher levels regularly in regions with significant foot traffic. A significant positive association was observed between particulate matter (PM₂.₅ and PM₁₀) and microbial load (r = 0.842, p < 0.001 and r = 0.439, p < 0.05), suggesting that particulate pollutants facilitate microbial transport and persistence. SO₂ also demonstrated a strong association with microbial concentration (r = 0.943, p < 0.001), indicating synergistic chemical–biological interactions in the urban environment. Representative pure isolates were screened microbiologically, yielding a variety of Gram-negative bacillary morphotypes, with select strains exhibiting α-hemolytic and β-mediated pathogenic characteristics. These results demonstrate a connection between particle pollution from vehicle emissions and the dynamics of airborne microbes, supporting the incorporation of microbiological markers into urban air quality evaluation systems.