This report documents the formulation of the GEOMET Indoor-Outdoor Air Pollution (GIOAP) model. The model estimates indoor air pollutant concentrations as a function of outdoor pollutant levels, indoor pollutant generation sources rates, pollutant chemical decay rates, and air exchange rates. Topics discussed include basic principles, model formulation, parameter estimation, model statistical validation, and model sensitivity to perturbations of the input parameters. The numerical estimates obtained from the GIOAP simulations have been validated with observed hourly pollutant concentrations obtained from an 18-mo residential air quality sampling program. Statistically the GIOAP model estimations are within 25% of the ideal condition (estimated and observed values coincide) for 85% of the observed values for CO, NO, NO2, NMHC, and CO2. The model has not been validated against sulfur dioxide owing to the very low values measured both indoors and outdoors. The predetermined validation criteria were not satisfied by the ozone model estimations; however, the calculated values were judged adequate because for about 85% of the observed values the predicted concentrations were within 2 ppb. Sensitivity studies on the GIOAP model parameters indicate that errors in the estimation of the initial condition and the volume of the structure dissipate with time. Errors in estimating the air exchange rate, the indoor generation strength, and the indoor chemical decay rate are more significant. Sensitivity coefficients have been formulated for all input parameters. The transient term is a unique feature of the GIOAP model; the impact of this term is substantial for stable pollutants but insignificant for ozone, which is a high reactive pollutant. The GIOAP Model, validated against a variety of measured data, satisfactorily predicts indoor pollutant concentrations, and it can be used to determine residential pollution levels under any conditions.

Project officer: Steven M. Bromberg. Scientific report. Sponsored by U.S. Dept. of Housing and Urban Development, Office of Policy Development and Research and Environmental Monitoring and Support Laboratory, Office of Research and Development.