Stochastic modeling of short-term exposure close to an air pollution source in a naturally ventilated room: an autocorrelated random walk method.
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.
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.
Kai-Chung
KC
Cheng
Civil and Environmental Engineering Department, Stanford University, Stanford, California, USA.
Viviana
V
Acevedo-Bolton
Civil and Environmental Engineering Department, Stanford University, Stanford, California, USA.
Ruo-Ting
RT
Jiang
Civil and Environmental Engineering Department, Stanford University, Stanford, California, USA.
Neil E
NE
Klepeis
Civil and Environmental Engineering Department, Stanford University, Stanford, California, USA.
Wayne R
WR
Ott
Civil and Environmental Engineering Department, Stanford University, Stanford, California, USA.
Peter K
PK
Kitanidis
Civil and Environmental Engineering Department, Stanford University, Stanford, California, USA.
Lynn M
LM
Hildemann
D000397:Air Pollution; D004781:Environmental Exposure; D011336:Probability; D013269:Stochastic Processes; D014691:Ventilation