A model to predict the breathing zone concentrations of particles emitted from surfaces Jonathan Thornburg, * a John Kominsky, b G. Gordon Brown, a Peter Frechtel, a William Barrett c and Glenn Shaul c Received 17th September 2009, Accepted 18th January 2010 First published as an Advance Article on the web 10th February 2010 DOI: 10.1039/b919385e Activity based sampling (ABS) is typically performed to assess inhalation exposure to particulate contaminants known to have low, heterogeneous concentrations on a surface. Activity based sampling determines the contaminant concentration in a person’s breathing zone as they perform a scripted activity, such as raking a specified area of soil, while wearing appropriate sample collection instrumentation. As an alternative approach, a probabilistic model based on aerosol physics and fluid dynamics was developed to predict the breathing zone concentration of a particulate contaminant emitted from a surface during activities of variable intensity. The model predicted the particle emission rate, tracked particle transport to the breathing zone, and calculated the breathing zone concentration for two scenarios. One scenario used an Eulerian model based on a Gaussian concentration distribution to quantify aerosol exposure in the trailing wake of a moving object. The second scenario modeled exposure in a quiescent environment. A Lagrangian model tracked the cumulative number of individual particles entering the breathing zone volume at a particular time. A Monte Carlo simulation calculated the breathing zone concentration probability distribution for each scenario. Both models predicted probability distributions of asbestos breathing zone concentrations that bracketed experimentally measured personal exposure concentrations. Modeled breathing zone concentrations were statistically correlated (p-value < 0.001) with independently collected ABS concentrations. The linear regression slope of 0.70 and intercept of 0.03 were influenced by the quantity of ABS data collected and model parameter input distributions at a site broader than those at other sites. Introduction Personal exposure assessment measures or evaluates the quantity of a contaminant that reaches a target at a specific frequency for a known duration. Personal exposure assessment, if done prop- erly, provides more representative exposure data than stationary area monitors. An advantage is that the duration and proximity of the person to the sources of the contaminant are accounted for by the measurement. 1 Therefore, personal exposure measurements typically have a stronger statistical relation with dose and risk. 2 Exposure assessment approaches for inhalation, dermal, and dietary routes include contaminant concentration measurements, biomarkers, surveys, historical reconstruction, deterministic models, and statistical models. 3 Measurement of the contami- nant concentration in the breathing zone is a common technique for inhalation exposure assessment. Accurate characterization of the breathing zone concentration is critical for the classical risk paradigm that links source emission rates to micro-environ- mental concentrations to a person’s exposure. Therefore, personal exposure measurements determine the inhalation rate and concentration dependent dose that can cause adverse health effects. 4 General population studies and activity based sampling are common designs for obtaining experimentally measured breathing zone concentrations. General population studies characterize the personal exposure of a large cohort to a wide variety of air pollutants during their normal, daily activities. a RTI International, 3040 Cornwallis Road, Research Triangle Park, NC, 27709, USA. E-mail: jwt@rti.org b Environmental Quality Management Inc., 1800 Carillon Boulevard, Cincinnati, OH, 45240, USA c US EPA\ORD\NRMRL, 26 West Martin Luther King Drive, Cincinnati, OH, 45268, USA Environmental impact Activity based sampling is the current standard method for assessing exposure to hazardous particles emitted from surfaces. This research presents an aerosol physics and fluid dynamics based model to predict the breathing zone concentration as a more economical alternative. This model is meant to be a screening tool to aid decision making. At one level, the model helps to identify whether the risk of adverse health outcomes is sufficient to justify collection of experimental data to confirm the modeled personal exposure estimates. Also, the model output extrapolates a limited range of experimental data to other exposure scenarios to understand the range of potential breathing zone concentrations. This journal is ª The Royal Society of Chemistry 2010 J. Environ. Monit., 2010, 12, 973–980 | 973 PAPER www.rsc.org/jem | Journal of Environmental Monitoring Downloaded by University of Nevada - Las Vegas on 01 September 2010 Published on 10 February 2010 on http://pubs.rsc.org | doi:10.1039/B919385E View Online