Evaluation of a Probabilistic Exposure Model Applied

Area of Science:

• Environmental Health
• Exposure Science
• Air Quality Modeling

Background:

• The U.S. Environmental Protection Agency (EPA) developed the probabilistic National Ambient Air Quality Standards (NAAQS) Exposure Model for carbon monoxide (pNEM/CO).
• This model estimates population exposure to carbon monoxide (CO) and carboxyhemoglobin (COHb) levels.

Purpose of the Study:

• To evaluate the performance of the pNEM/CO model.
• To compare simulated CO exposure distributions with observed data from a Denver Personal Exposure Monitoring Study (PEM).

Main Methods:

• The pNEM/CO model was configured to simulate CO exposure data from the 1982-1983 Denver PEM study.
• Observed and simulated cumulative relative frequency distributions of CO exposure were compared for 779 subjects.
• Comparisons were made for 1-hour daily maximum exposure (1DME) and 8-hour daily maximum moving average exposure (8DME).
• Subjects were categorized based on home stove type (gas or electric).

Main Results:

• For 1DME, pNEM/CO showed closest agreement between 6-13 ppm, overestimating low (<6 ppm) and underestimating high (>13 ppm) exposures.
• For 8DME, the model best matched observed exposures between 5.5-7 ppm.
• The model over-predicted occurrences below 5.5 ppm and under-predicted above 7 ppm for 8DME.

Conclusions:

• The pNEM/CO model demonstrates reasonable performance within specific exposure ranges.
• Model accuracy is limited at the extremes of the exposure distribution.
• Further refinement may be needed to improve predictions at low and high CO exposure levels.