Comparison of chemical composition and airborne bacterial community structure in PM2.5 during haze and non-haze days in the winter in Guilin, China.

Haze is a typical type of air pollution and frequently has occurred in the winter in Guilin city recently, but information relating to chemical compositions and airborne bacterial community structure of atmospheric particulate matter (PM2.5) during haze days remains very limited. In this study, the PM2.5 concentration, chemical components including water-soluble ions and metal elements, and bacterial community compositions of PM2.5 on both haze and non-haze days were characterized, and the relationships between them were studied. The results showed that levels of the secondary aerosol particles of SO42-, NO3-, and NH4+ in haze PM2.5 associated with local fuel combustion and vehicle emissions were significantly higher than non-haze samples. Similar trends were observed for the detected trace metal elements. High-throughput sequencing results indicated that higher PM2.5 concentration caused lower bacterial richness and diversity. However, the airborne bacterial community structure remained stable, and no significant difference was found between haze and non-haze PM2.5. Firmicutes, Proteobacteria, and Bacteroidetes were the most abundant phyla accounting for a total of 97.2% on average. In contrast to non-haze PM2.5, the bacterial community structure of haze PM2.5 was mostly positively correlated with SO42-, NO3-, NH4+, K+, and Cl-, suggesting these secondary aerosol particles were probably of great importance on haze pollution and variability of the bacterial compositions of PM2.5.