Recent research progress and perspective of characteristics of ambient bioaerosols during hazy pollution in China

Abstract

Since the haze event occurred in many areas of central and eastern China in 2013, haze pollution has become one of the most important environmental issues and has attracted more and more attention from government, industry circle, scholars and the general public in China. Haze pollution is characterized by atmospheric particular matter (PM) being one of the top pollutants. A large number of studies have been conducted to investigate the chemical components of atmospheric PM during haze pollution, while little is known about the biological components and characteristics of PM in the atmosphere, especially during haze pollution. Biological particles in the atmosphere, generally defined as bioaerosols, are airborne particles or large molecules carrying living organisms or released from living organisms (e.g., bacteria, fungi, viruses, pollen, bacterial endotoxins and mycotoxins, etc.). Bioaerosols not only pose potential risks on air quality and human health, but also have direct effects on the alteration of global climate and atmospheric physical and chemical processes. Up to now, however, the concentration and size distribution, diversity, and abundance of different types of bioaerosols as well as their temporal and spatial variability are not well characterized on hazy days. Moreover, due to the changeable community structure, flexible biological activity and comprehensive influential factors, the knowledge involving how haze pollution affects bioaerosols, to what extent it affects, and the influence mechanism is still unclear so far. Therefore, this review first has presented an overview of the state of bioaerosol research during haze pollution, including concentration level, size distribution and community structure of microorganisms in bioaerosols. Subsequently, the current understanding and open questions have been emphatically discussed concerning the characteristics of bioaerosols at different air pollution levels and effects of air pollution on airborne microbes. Finally, we suggest that the following research activities should be pursued in future studies of bioaerosols during haze pollution: (1) It is extremely urgent to develop and establish uniform standardized sampling and identification criterion to better judge and measure the numerous monitoring data from different researchers. It is also essential to develop advanced, sensitive, real-time and online detection techniques to quantify the biological properties of bioaerosols. (2) The nationwide field monitoring of bioaerosols covering more climate types and pollution levels at various time scales should be carried out to obtain more comprehensive data for fully understanding the temporal and spatial variability of bioaerosols and its influential factors. Some other meteorological influential factors (e.g., boundary-layer height, atmospheric extreme temperature, extreme wind speed, and atmospheric pressure, etc.), and pollution factors such as the concentration of heavy metal and polycyclic aromatic hydrocarbon (PAHs) in PM should be taken into account to deeply understand the effect of haze pollution on bioaerosols. (3) Current studies have shown that many gaseous and particulate pollutants are related to the concentration of bioaerosols. However, little is known about the influence mechanisms of pollutants. Therefore, in addition to field monitoring, it is also necessary to design and conduct the laboratory experiment of smog chamber to determine the influence mechanism of each single environmental factor or pollution factor on bioaerosols. (4) In addition to different degrees of haze pollution, there are different kinds of haze pollution including the formation of haze by photochemical reaction in summer and liquid phase reaction at high RH in winter. Therefore, it is also essential to examine the distribution and variation of bioaerosols during different haze formation processes in order to improve our understanding of haze pollution effects on bioaerosols. (5) It is necessary to develop a biological source-tracking technology based on the bioaerosol species and community composition to reveal the possible sources of bioaerosols during haze episodes.