Measurement of the proximity effect for indoor air pollutant sources in two homes

Abstract

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.

Outdoor fine and ultrafine particle measurements at six bus stops with smoking on two California arterial highways—Results of a pilot study

“…The breathing zone of this person, who was 1.8 m (5 feet 10 inch) tall, was approximately 1.6 m above the sidewalk, whereas the sitting smoker's breathing zone was approximately 1 m above the sidewalk, and the greater height may explain the lower exposure of the standing person compared with the exposure of the nonsmokers on the bench. An experimental indoor air quality proximity study with an array of up to 37 CO monitors reported that the highest concentrations occurred at the same height as the source (Acevedo-Bolton et al, 2012), and a similar phenomenon could apply to smoking outdoors.…”

“…The high concentrations and wide ranges can be attributed to the multiple microplumes reaching each person. Acevedo-Bolton et al (2012) reported a proximity study in which adjusting the exposure by subtracting a small quantity from each measurement improved the linearity of the distributional fit. The quantity they subtracted-obtained by using a trial-and-error approach maximizing R 2 -was very small.…”

“…The result of introducing this small incremental concentration that is subtracted causes a third parameter to be added to the twoparameter lognormal model, making it a three-parameter lognormal model, and the incremental parameter is called the shift parameter (Acevedo-Bolton et al, 2012). The adjusted concentrations fit to the lognormal model with geometric mean m g and geometric standard deviation s g all had R 2 values of 96.7% or higher (Table 4).…”

“…The breathing zone of this person, who was 1.8 m (5 feet 10 inch) tall, was approximately 1.6 m above the sidewalk, whereas the sitting smoker's breathing zone was approximately 1 m above the sidewalk, and the greater height may explain the lower exposure of the standing person compared with the exposure of the nonsmokers on the bench. An experimental indoor air quality proximity study with an array of up to 37 CO monitors reported that the highest concentrations occurred at the same height as the source (Acevedo-Bolton et al, 2012), and a similar phenomenon could apply to smoking outdoors.At one site, Bus Stop D, we reversed the order of the participants with respect to the direction of traffic. Here, the smoker's breathing-zone exposure for both cigarettes (26 and 88 mg/m 3 ) turned out to be lower than at the other sites, so turbulence caused by the moving traffic may have reduced the smoker's exposure.…”

“…This small adjustment moved the frequency distributions of the standing person and the background concentrations further downward at the smaller percentiles than at the larger percentiles, causing the lines on the graph to straighten. A physical interpretation of this adjustment may be that it helps separate the two concentration components that make up the background concentration measured on the sidewalk: the outdoor ambient concentration from more distant sources and the concentration caused by pollutant emissions from traffic on the adjacent roadway, which combine to make up the background concentration on the sidewalk.The result of introducing this small incremental concentration that is subtracted causes a third parameter to be added to the twoparameter lognormal model, making it a three-parameter lognormal model, and the incremental parameter is called the shift parameter (Acevedo-Bolton et al, 2012). The adjusted concentrations fit to the lognormal model with geometric mean m g and geometric standard deviation s g all had R 2 values of 96.7% or higher (Table 4).…”