TRJ Environmental


Exposure Assessment

NEM, pNEM, and pHAP. Ted Johnson has contributed directly to the development and implementation of all versions of the NAAQS Exposure Model (NEM and pNEM). This model has been used by the Air Quality Management Division (AQMD) of EPA to assess population exposure to ozone, carbon monoxide, sulfur dioxide, nitrogen dioxide, and particles. Health Canada has used NEM to assess exposures to ozone, carbon monoxide, benzene, and 1-3 butadiene. His work relating to NEM and pNEM includes fitting of distributions to air quality data, estimation of missing air quality values through the use of Fourier analysis, estimation of extreme values, development of indoor/outdoor relationships, development of pollutant-specific rollback models, and development of human activity patterns. He has also developed Monte Carlo algorithms for simulating gas stove emissions, human ventilation rates, and home-to-work commuting patterns. He developed a special version of pNEM for application to hazardous air pollutants (pHAP).

APEX. Ted Johnson is currently assisting in the development of the Air Pollution Exposure Model (APEX), EPA’s state-of-the-art exposure model. He recently worked with William McDonnell and Marjo Smith to develop an output module for APEX-Ozone that can be used to estimate minute-by-minute FEV1 decrements as a function of ozone concentration and ventilation rate.

HAPEM. Ted Johnson has contributed directly to the development and implementation of all versions of the Hazardous Air Pollutant Exposure Model (HAPEM). The standard version of this model is used by the EPA in estimating exposure and risks associated with hazardous pollutants emitted from point and area sources. A special version of HAPEM is used by the Office of Mobile Sources to estimate risks associated with mobile sources. Mr. Johnson's work related to these models included design of the basic exposure model, development of a special model for estimating commuting patterns based on census data, and development of a program for extrapolating city-specific risk estimates to regions. He has recently assisted in developing microenvironment factors and commuting algorithms for an enhanced version of HAPEM used in the National Air Toxics Assessment (NATA).

TRIM. Ted Johnson coordinated model design work for the Total Risk Integrated Model (TRIM). This model is currently being developed by EPA to simulate pollutant movement through various media and to estimate resulting exposure and risk in human populations. Mr. Johnson served as head of the TRIM development team during 1996 and 1997. Jill Mozier conducted an in-depth evaluation of existing exposure models to identify modeling methods that could be incorporated into TRIM, as well as locating databases which could be used as model inputs. She completed a report summarizing her literature review efforts which included recommendations for the future development of TRIM.

Guide to OAQPS Exposure Models. Ted Johnson prepared the 550-page document “A Guide to Selected Algorithms, Distributions, and Databases Used in Exposure Models Developed by the Office of Air Quality Planning and Standards,” the only comprehensive guide to the exposure modeling tools developed by OAQPS. (STAR grant no. CR827033.)

Benzene Exposure Model. Ted Johnson developed the Benzene Exposure Model (BEM) for the American Petroleum Institute and used the model to estimate incremental human exposures to benzene from bulk storage facilities and petroleum refinery waste streams.

SimRisk. Ted Johnson developed SimRisk for the American Petroleum Institute and used the Monte Carlo model to estimate population exposures to benzene emitted by glycol dehydrators and multiple pollutants emitted by offside treatment facilities. He recently developed a special version of SimRisk applicable to styrene emissions from fiberglass manufacturing facilities.

EPEM. Ted Johnson developed the Event Probabilitiy Exposure Model (EPEM) for the Motor Vehicles Manufacturers Association and used the model to determine likelihood of high ozone exposures in urban populations.

Ventilation (Respiration) Rates for Dosimetry Models. The APEX and pNEM exposure models include algorithms capable of generating sequences of ventilation estimates specific to demographic group. With the assistance of Jim Capel, Ted Johnson developed a stand-alone program that (1) combined the current APEX/pNEM ventilation rate algorithm with the Consolidated Human Activity Database (CHAD); (2) enabled the user to construct custom demographic groups (cohorts) defined by age, gender, disease status, and other factors; and (3) produced ventilation rate estimates with averaging times specified by the user to match the intended use. Johnson and Capel also prepared a user’s manual for the program.