| Bioaerosols are a significant group of atmospheric aerosols, and have an important effect on global climate change, human health and environmental quality. They are mainly derived from biological activities in the terrestrial and aquatic environments, including fungi, bacteria, viruses, pollens, disintegration of plants and animals, and other active substances. Airborne microorganisms are an important component of bioaerosols. The microbial activity in bioaerosols can indirectly affect the cloud formation and the global climate, and can also cause a potential environmental health risk for human beings.In this study, the microbial activity in bioaerosols collected in the Qingdao coastal region was investigated using the FDA (fluorescein diacetate) hydrolysis method, from Mar.2013 to Feb.2014. We analysed the seasonal distribution of bioaerosol microbial activity in outdoor environment in Qingdao and also discussed the influences of meteorological factors and weather conditions on bioaerosol microbial activity.The results we obtained showed that the microbial activity ranged from 5.49 to 102 ng/m3 sodium fluorescein, with an average of 34.4 ng/m3 sodium fluorescein, from Mar.2013 to Feb.2014. The microbial activity level in the atmospheric environment was lower by several orders of magnitude than those in soil and water.The average microbial activity showed a seasonal variation in Qingdao, with a trend of summer (Jun., Jul., Aug.)> autumn (Sep., Oct., Nov.)> winter (Dec, Jan., Feb.)> spring (Mar., Apr., May.). The seasonal differences were clearly significant (*p<0.05), except for the differences between summer and autumn, and between winter and spring. The microbial activity level in bioaerosols was relatively low in the winter and spring, while the variation range was smaller than in the summer and autumn, which may due to the environmental differences of microbial sources, meteorological factors and weather conditions in varied seasons.The monthly average bioaerosol microbial activity was in the range of 14.3-76.9 ng/m3 sodium fluorescein throughout 2013, presenting a rise from the beginning of Mar. and decreasing after Aug. The lowest monthly average activity presented in Mar., while the highest level was in Aug. In Jun. and Sep., the microbial activity level varied in a larger range than in the other months, with both months exhibiting an SD (standard deviation) value of up to 39. The variation of temperature is the main reason leading to the monthly variation of microbial activity in bioaerosols, together with the effects of special weather conditions such as fog, haze, rain and dust.The size distribution of microbial activity in bioaerosols in Qingdao presented as higher in coarse size than in fine size, i.e., it showed a higher microbial activity on particle size greater than 2.1μm than on particle size less than 2.1μm. No significant difference exists between different seasons and weather conditions for size distribution of microbial activity. The size distribution of microbial activity in bioaerosols is affected by the species and sources of microorganisms, and the size of microorganisms in turn can affect the microbial adhesion and atmospheric transportation process.Microbial activity in bioaerosols is influenced by various meteorological factors. Multiple linear regression analysis was performed and results showed that meteorological factors such as atmospheric temperature, relative humidity and wind speed accounted for approximately 35.7% of the variation of the microbial activity, although their individual impacts on microbial activity varied. According to the correlation analysis, atmospheric temperature and wind speed had a significant positive and negative influence on microbial activity, respectively, while relative humidity and wind direction had no significant influence. However, relative humidity can change microbial amount by altering its environment and wind direction is closely related to microbial sources, which may indirectly affect microbial activity.The microbial activity was also affected by weather conditions. Microbial activity in bioaerosols differed in different weather conditions such as sunny, foggy, hazy and rainy days of different seasons. But the reason remains unclear for the variation of microbial activity in bioaerosols under different weather conditions.It may be connected with the change of physical or chemical state of atmospheric environment with the alteration of weather, and also affected by the atmospheric transportation process. Dust would result in higher microbial activity level, but it still needs more data to verify. Therefore further practical observations are desired to better understand the distribution characteristics of activity in bioaerosols and the influence mechanism of the environmental factors on microbial activity.Microbial activity in bioaerosols can serve as air quality indicator and indirectly reflect the degree of environmental pollution and its harm to human body health. During Mar.2013 to Feb.2014, microbial pollution caused slight harm to environmental quality and human health when air quality index (AQI) was in the range of 0-200. More attention should be paid to the health risk caused by microbial exposure when the air is seriously polluted. In order to perform the microbial risk assessment (MRA), further research is needed to determine the dose-response relationship between the microbial activity and viral infection,and the threshold value of microbial activity as well. |
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