Characteristics of bioaerosols under high-ozone periods, haze episodes, dust storms, and normal days in Xi’an, China

Abstract

The characteristics of bioaerosols and their effects on human beings’ health have become a major public concern in the recent years. This study compared the characteristics of bioaerosols under different types of pollution (high-ozone [HO] episodes, haze episodes, and dust storms [DSs]), with those of bioaerosols on normal days (NDs) in Xi'an, China. The concentrations, diurnal variations, and size distribution of bacteria, fungi, and total airborne microbes (TAMs) were investigated. The results showed that the bacterial and fungal concentrations were the highest during DSs and on NDs, reaching 425.2 and 956.9 colony-forming units/m3, respectively. The concentration of TAMs was the highest during HO episodes, reaching 10.7 × 106 cells/m3, which was significantly higher than that during the other events. The maximum concentrations of bacteria and fungi during HO episodes were observed in the morning, while they appeared separately in the morning and evening during haze episodes. Bacteria and TAMs during DSs reached peak concentrations in the morning and evening, which is opposite to the particulate matter (PM) distribution pattern. On NDs, temperature and relative humidity had significant effects on bioaerosols. The size distributions of airborne bacteria exhibited bimodal patterns, whereas unimodal distributions were observed for fungi. Fungi mainly attached in fine particles (<2.1 μm) with proportions of 67.4% and 60.5% during haze episodes and DSs, respectively, which means that fungi were easily penetrated into the human respiratory system. The evaluation of influence factors revealed that PM2.5 and PM10 had negative effects on fungal concentration during DSs, and ozone concentration and temperature were inversely correlated with fungal concentration during HO episodes. These results provide valuable reference data for elucidating the formation and evolution of bioaerosols under different types of pollution.