Cheng Kai-Chung, Acevedo-Bolton Viviana, Jiang Ruo-Ting, Klepeis Neil E, Ott Wayne R, Kitanidis Peter K, Hildemann Lynn M
1] Civil and Environmental Engineering Department, Stanford University, Stanford, California, USA [2] Indoor Air Quality Section, Environmental Health Laboratory, California Department of Public Health, Richmond, California, USA.
Civil and Environmental Engineering Department, Stanford University, Stanford, California, USA.
J Expo Sci Environ Epidemiol. 2014 May-Jun;24(3):311-8. doi: 10.1038/jes.2013.63. Epub 2013 Sep 25.
For an actively emitting source such as cooking or smoking, indoor measurements have shown a strong "proximity effect" within 1 m. The significant increase in both the magnitude and variation of concentration near a source is attributable to transient high peaks that occur sporadically-and these "microplumes" cause great uncertainty in estimating personal exposure. Recent field studies in naturally ventilated rooms show that close-proximity concentrations are approximately lognormally distributed. We use the autocorrelated random walk method to represent the time-varying directionality of indoor emissions, thereby predicting the time series and frequency distributions of concentrations close to an actively emitting point source. The predicted 5-min concentrations show good agreement with measurements from a point source of CO in a naturally ventilated house-the measured and predicted frequency distributions at 0.5- and 1-m distances are similar and approximately lognormal over a concentration range spanning three orders of magnitude. By including the transient peak concentrations, this random airflow modeling method offers a way to more accurately assess acute exposure levels for cases where well-defined airflow patterns in an indoor space are not available.
对于烹饪或吸烟等主动排放源，室内测量表明在1米范围内存在强烈的“近距离效应”。源附近浓度的大小和变化显著增加，这归因于偶尔出现的瞬态高峰值，而这些“微羽流”在估计个人暴露量时会造成很大的不确定性。最近在自然通风房间进行的现场研究表明，近距离浓度近似呈对数正态分布。我们使用自相关随机游走方法来表示室内排放的时变方向性，从而预测靠近主动排放点源处浓度的时间序列和频率分布。预测的5分钟浓度与自然通风房屋中一氧化碳点源的测量结果吻合良好——在0.5米和1米距离处测量和预测的频率分布相似，并且在跨越三个数量级的浓度范围内近似呈对数正态分布。通过纳入瞬态峰值浓度，这种随机气流建模方法为在室内空间没有明确气流模式的情况下更准确地评估急性暴露水平提供了一种方法。
