Acevedo-Bolton Viviana, Cheng Kai-Chung, Jiang Ruo-Ting, Ott Wayne R, Klepeis Neil E, Hildemann Lynn M
Civil and Environmental Engineering Dept, Stanford University, Stanford, CA 94305, USA.
J Environ Monit. 2012 Jan;14(1):94-104. doi: 10.1039/c1em10521c. Epub 2011 Nov 8.
Personal exposure to air pollutants can be substantially higher in close proximity to an active source due to non-instantaneous mixing of emissions. The research presented in this paper quantifies this proximity effect for a non-buoyant source in 2 naturally ventilated homes in Northern California (CA), assessing its spatial and temporal variation and the influence of factors such as ventilation rate on its magnitude. To quantify how proximity to residential sources of indoor air pollutants affects human exposure, we performed 16 separate monitoring experiments in the living rooms of two detached single-family homes. CO (as a tracer gas) was released from a point source in the center of the room at a controlled emission rate for 5-12 h per experiment, while an array of 30-37 real-time monitors simultaneously measured CO concentrations with 15 s time resolution at radial distances ranging from 0.25-5 m under a range of ventilation conditions. Concentrations measured in close proximity (within 1 m) to the source were highly variable, with 5 min averages that typically varied by >100-fold. This variability was due to short-duration (<1 min) pollutant concentration peaks ("microplumes") that were frequently recorded in close proximity to the source. We decomposed the random microplume component from the total concentrations by subtracting predicted concentrations that assumed uniform, instantaneous mixing within the room and found that these microplumes can be modeled using a 3-parameter lognormal distribution. Average concentrations measured within 0.25 m of the source were 6-20 times as high as the predicted well-mixed concentrations.
由于排放物的混合并非瞬间完成，在靠近活动源的区域，个人接触空气污染物的程度可能会显著更高。本文所呈现的研究对加利福尼亚州北部（CA）两座自然通风住宅中一个非浮力源的这种近距离效应进行了量化，评估了其空间和时间变化以及诸如通风率等因素对其强度的影响。为了量化与室内空气污染物住宅源的接近程度如何影响人体暴露，我们在两座独立的单户住宅的客厅中进行了16次单独的监测实验。在每个实验中，CO（作为示踪气体）以受控的排放速率从房间中央的点源释放5至12小时，同时，在一系列通风条件下，一组30至37个实时监测器以15秒的时间分辨率在0.25至5米的径向距离上同时测量CO浓度。在靠近源（1米范围内）测得的浓度变化很大，5分钟平均值通常相差超过100倍。这种变化是由于在靠近源的位置经常记录到持续时间较短（<1分钟）的污染物浓度峰值（“微羽流”）。我们通过减去假设房间内均匀、瞬间混合的预测浓度，从总浓度中分解出随机的微羽流成分，发现这些微羽流可以用三参数对数正态分布来建模。在距离源0.25米范围内测得的平均浓度比预测的充分混合浓度高6至20倍。
