Abstract
Particulate matter (PM), a major air pollutant in Beijing in recent years, poses a formidable public health threat. Even through many studies have documented the chemical and biological characteristics of PM, less is known about these characteristics on hazardous haze days (Air Quality Index, AQI 301-500) and the difference with sunny or unhealthy haze day (AQI 151-200) characteristics. Herein, studies were performed during a red alert air pollution event (continuous hazardous haze days) and the first few days following the event (sunny days first and then unhealthy haze days) in Beijing from December 19 to 25, 2016. A laser particle counter and an ANDERSEM-6 sampler were used to study the concentration and size distributions dynamics of the PM and the culturable airborne bacteria and fungi, respectively. PM2.5 was sampled by a high-volume air sampler and the chemical compositions, bacterial and fungal community structures, and endotoxin levels were analyzed. The results showed that the PM concentrations on the hazardous haze days and unhealthy haze days were 10.7 and 8.0 times higher, respectively, than those on the sunny days. The chemical composition of PM2.5 was highly correlated with the AQI. The concentration and percentage of water-soluble inorganic ions (WSII), which dominated the PM2.5 constituents, as well as the levels of endotoxin were higher on hazardous haze days than on unhealthy haze days and sunny days. Interestingly, the abundances of bacteria and fungi demonstrated the following order: unhealthy haze days> sunny days> hazardous haze days. Most culturable bacteria and fungi were distributed in particles with aerodynamic diameters of 2.1-4.7 μm. Redundancy analysis found total organic carbon explained 30.0% and 27.1% of total variations in bacterial composition and fungal composition at the genera level, respectively. Our results facilitate a better understanding of the biological and chemical composition dynamics of PM in Beijing.