Models of exposure to carbon monoxide inside a vehicle on a Honolulu highway

This paper presents statistical models of passenger exposure to carbon monoxide (CO) inside a motor vehicle as it traveled a coastal highway in Honolulu, Hawaii during morning periods between November, 1981 and May, 1982. The 3.85-mile study site was divided into three links. The models predict the average CO concentration inside the vehicle's passenger cabin on the third link as a function of several variables: the average CO concentrations inside the cabin on previous links; traffic, temporal, and meteorological variables; motor vehicle CO emission factors; and ambient CO concentrations. Based on data for 80 trips, the three most powerful models (adjusted R2 = 0.69) were nonlinear combinations of four variables: the average CO concentration inside the cabin for the second link; wind speed and direction; and either the travel time, vehicle speed or CO emission factor for the third link. Several nonlinear models were based on data for 62 trips for which nonzero, ambient CO concentrations were available. For this database, the most practical models (adjusted R2 = 0.67) combined three variables: the ambient CO concentration; the second-link travel time; and either the travel time, vehicle speed or CO emission factor for the third link. Two factors of third-link CO exposure varied seasonally. Relatively lighter traffic flows and stronger winds lowered cabin exposures during late fall, while heavier traffic flows and calmer winds elevated cabin exposures during winter and spring. This study confirms the importance of seasonal effects on cabin exposure, as observed by a California study, and adds new insights about their effects.