北京典型地区大气细菌气溶胶活性特征及其影响因素研究

Bacterial aerosols are reported to play important roles in the atmospheric physical and chemical processes and have a significant impact on human health. In what ways and to what extent do the bacterial aerosols affect the atmosphere processes and human health? This is closely related with the viability of bacterial aerosols, including viable bacterial concentration, as well as the ratio of viable bacteria to the total bacteria. Normally, concentration of culturable bacteria is applied for assessing the bacterial aerosol viability, which leads to a substantial underestimation of viable bacterial aerosols. Furthermore, the factors affecting the viability of bacterial aerosols are still uncertain. This proposal intends to investigate the viability of bacterial aerosols and the corresponding influencing factors in Beijing during a one-year period. The campaign will be conducted in the suburb area Changping district and central urban area Haidian district of Beijing in four seasons, under typical meteorological parameters and air pollution levels. Electrostatic sampler showing low viability loss during sample collection will be applied in combination with filter sampler. Viability Quantitative polymerase chain reaction (qPCR) using propidium monoazide (PMA) will be used to determine the viable and total bacterial concentration. The diurnal variation, seasonal changes, as well as spatial distribution of the viability of bacterial aerosols will be obtained. Combined with the multivariate statistical model, the relationship between the bacterial aerosol viability and meteorological parameters as well as air pollutants will be inferred. Verifying test for these inferred factors with smoke chamber simulating the actual particle-free ambient environment and direct aqueous exposure will be performed. The factors influencing the bacterial aerosol viability will be elucidated. The results obtained from this study will improve the understanding on the relationship between bacterial aerosols and air pollution, thereby give further information on assessing the impact of bacterial aerosols on the atmosphere and human health.

细菌气溶胶会影响人体健康及大气物理、化学过程，影响方式和程度与其活性（活菌浓度、活菌占总细菌的比例等）密切相关。目前主要采用可培养活菌评估细菌气溶胶活性，显著低估了活菌浓度，且对影响其活性的环境因素尚不明确。本项目拟在北京昌平（郊区）和海淀（中心城区）地区，采用滤膜和低细菌损伤的静电场采样器相结合的方法，采集代表性气象和大气污染水平条件下的细菌气溶胶样品；利用PMA-qPCR方法，分析活菌浓度及活菌占比，用于评价细菌气溶胶活性，获得细菌气溶胶活性的时间（日和季）和空间（郊区和中心城区）分布特征；基于多元统计模型，探讨细菌气溶胶活性与气象条件、大气污染物及大气环境质量的关系；在此基础上，开展基于准实际大气环境的烟雾箱气相暴露和直接混合的液相暴露实验，研究气象因素和大气污染物对细菌气溶胶活性的影响。研究成果有助于理解大气污染和细菌气溶胶的关系，可为评估细菌气溶胶健康风险及环境影响提供基础数据。

大气污染和气候变化近年来快速推动了大气物理化学过程的研究和科学认识，然而关于大气中可能存在的大气生物过程的科学认知却非常少。大气环境作为微生物的传播通道，其作为一个生态系统的潜在可能和意义未受到重视。由于环境大气中缺乏微生物生长繁殖必须的营养环境条件，且微生物含量相对较低，一定程度上导致了对大气中微生物过程的忽视。基于此，本项目选择以环境大气中悬浮的细菌气溶胶为研究对象，对其活性特征和影响因素开展深入研究，以此作为研究大气生物过程的起点和基础。本项目中结合基于激光诱导荧光的生物气溶胶在线监测数据，发现有活性的生物气溶胶浓度波动较大，有较为明显的日间低、夜间高的昼夜分布趋势，粒径分布主要分布在2–3 µm之间，总体上其浓度水平、粒径分布和背景点有显著不同，受人群影响较为显著，基本形成了对北京地区有活性的生物气溶胶特征概况认识。结合基于细胞膜完整性的细菌活性、可培养活性、细菌代谢活性等活性评价方法，评估了北京地区的细菌气溶胶活性，发现细菌气溶胶中有活性的部分浓度占比波动较大，从每立方米空气几十个到几十万个不等，沙尘等特殊天气爆发时会进一步导致有活性的细菌气溶胶活性上升。细菌气溶胶活性受细颗粒物、可吸入颗粒物、二氧化氮、臭氧等污染物直接影响。实验室模拟实验表明细菌气溶胶在受到污染物暴露影响时，可在分子层面通过基因表达调控胞内氧化应激响应，用以应对外部环境胁迫压力。上述研究结果意味着，细菌气溶胶在环境大气不仅是被动悬浮，同时具备应对大气环境胁迫压力的主动响应能力，该代谢过程反过来可能也会对大气环境过程产生影响，直接影响大气物理化学过程。