沉降在空调热交换器上的微生物气溶胶二次污染形成机制研究

Airborne microbes in the airstream could deposit onto air-conditioning heat exchanger surfaces and have various activities such as metabolic activity and reproduction using other deposited particles or heat exchanger materials as nutrients. Besides the increase of microbial biomass, many other pollutants such as endotoxins, allergens and microbial volatile organic compounds (MVOCs) can be generated from the microbes. These pollutants may be aerosolized or released into an indoor air environment under certain conditions and cause adverse health effects such as sick building syndrome and asthma. However, little is known about the spatial distribution of microbial aerosols after their deposition, as well as the generation process and mechanism of secondary pollutants, not to mention the mechanism of release and diffusion of secondary pollutants into indoor air. In this project, a unique laboratory Heating, Ventilation and Air Conditioning (HVAC) system is designed and used to systematically investigate the whole transformations of microbial aerosols across the heat exchanger. Firstly, the factors that affect microbial aerosols deposition will be revealed and the spatial distribution of microbial aerosols on the heat exchanger will be obtained. Secondly, based on the spatial distribution, the types and concentrations of pollutants generated by deposited microbial particles inside the heat changer system would be disclosed. Finally, the mechanism of generation, release and diffusion of secondary pollutants would be revealed through the combination of experimental data and model prediction. Moreover, health risks associated with secondary pollution will be also evaluated by combining cell toxicology testing in vitro and aerosol inhalation exposure experiment. The expected results of this project not only provide a more comprehensive theoretical basis and a more reliable investigation method to better understanding the influence mechanisms of HVAC on indoor air quality, but also provide an important reference for source apportionments and optimization control of microorganisms, allergens, endotoxins and MVOCs in indoor air.

微生物气溶胶可在空调热交换器表面沉降并进行代谢、繁殖等活动，一方面增加微生物量，另一方面生成内毒素、过敏原、MVOCs等污染物。这些污染物进入室内空气可引起负面健康问题，如病态建筑综合症、哮喘等。但是关于微生物气溶胶在热交换器上沉降后的空间分布，微生物二次污染物的生成过程与机制、二次污染物释放与扩散的机制尚无清楚的科学认识。本项目通过创建独特的空调通风系统，系统地研究微生物气溶胶在热交换器上的沉降及之后发生的整个过程，获得微生物气溶胶在热交换器上的沉降分布，明确沉降后的微生物生成的二次污染物的种类和浓度，并结合实验研究与模型研究阐明二次污染物的生成、释放和扩散机理。此外，结合体外细胞毒理实验和气溶胶动物吸入暴露实验评估二次污染的健康风险。本项目将为研究空调通风系统对室内空气的影响机制提供更全面的理论依据和研究方法，为室内空气中的微生物、过敏原和MVOCs等的源解析和优化控制提供重要参考。

现代建筑中的空调通风系统不可避免地接触输送到室内环境的空气，可直接影响室内环境和人员健康。当前对微生物气溶胶在空调系统尤其是热交换器表面的沉降及分布规律缺乏研究，而热交换器表面微生物的二次污染物的种类及浓度尚不清楚。为了系统地回答这些科学问题，本研究创建了一套具有独特热交换器的空调系统，揭示了微生物气溶胶在热交换器上的沉降分布特征，并结合实验与模型研究阐明了二次污染物的生成、释放机理。结果表明，空调热交换器表面总颗粒物与微生物气溶胶沉积分布规律并不一致，前者沿气流方向逐排下降，而后者主要分布在热交换器第二排背风面与第三排迎风面。微生物气溶胶在空调热交换器表面后产生的二次污染物包括子代微生物、过敏原和挥发性有机物等，主要与表面微生物沉降量、种类等相关。当热交换器表面形成生物膜后，热交换器下游空气的颗粒物数量有所增加，这主要是由于气流导致了翅片表面子代微生物（粒径主要集中在2-3μm）和真菌过敏原等二次污染物的重悬浮。本研究还发现空调热交换器下游空气暴露的大鼠血液中的白细胞介素6、C反应蛋白水平显著高于暴露在上游空气中的水平，且最大增幅为280%。而且，暴露组大鼠血液中的miR-146a，miR-146a和miR-26a的表达水平显著降低。这些研究结果表明暴露在空调热交换器下游空气期间大鼠体内产生了炎症反应，二次污染物暴露导致了负面健康效应。本项目不仅为研究空调通风系统对室内空气的影响机制提供更全面的理论依据和研究方法，也为室内空气中的微生物、过敏原和MVOCs等的源解析和优化控制提供重要参考。项目总体上很好地完成计划研究内容，在Journal of Hazardous Materials、Environmental Pollution等期刊上发表通讯作者论文3篇，合作文章10篇，发明专利3项，出版论著1本，参加7次国内外学术会议，举办1次国内会议，并培养1名博士生和9名硕士生。在本项目的支持下，项目负责人获得了2项山东省重点研发计划支持（2019GSF107071和2019RKE27003），同时项目负责人被授予中国环境科学学会室内环境与健康分会青委会副主任委员等学术荣誉。