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The Midac Fourier Transform Infrared air monitoring system was used to measure real-time vehicular exhaust emission concentrations of carbon monoxide (CO) and hydrocarbons (HCs) during the Purdue Vehicle Emission Monitoring and Modeling Project (PVEMP) conducted in spring and summer 1997. The experiments took place on the Borman Expressway, in Gary. Indiana and on 1-65, south of Lafayette, Indiana Concurrently, two speed-readings were acquired from the passing vehicles in the vicinity of the air monitoring system using a hand-held laser gun. The speeds were integrated to determine the speeds and accelerations of the passing vehicles at the spectrometer. An 8-mm camcorder was used to videotape the passing vehicles in order to determine the vehicle types. Three vehicle types were determined: type I represented all the automobiles, Type II represented all the medium-duty vehicles including light and medium duty trucks, pick-ups, and vans, and type III represented all the heavy-duty vehicle mainly semi-trailers. Meteorological data were also recorded from the nearest surface weather stations. Overall, 16,870 vehicles were monitored. 8,478 were type I vehicles, 4,829 were type II vehicles, and 3,563 were type III vehicles. The flow rates in count per minute were 8.92, for type I. 5.08 for type II. 3.75 for type III. and 17.75 for the combined fleet However, 4,413 vehicles were retained for data analysis. These included 2,848 (65%) type I vehicles and 1,565 (35%) type II vehicles. Type III vehicles were not included in the analysis because their exhaust emission concentrations were not measured. However, their counts and frequencies were determined.

The analysis of the PVEMP database showed that the exhaust emission concentrations were very variable with a logarithmic distribution. On average, type I vehicles exhaust emission concentrations were 1.10 % CO and 0.23 % HCs while that of type II vehicles were 1.16 % CO and 0.24 % HCs. They were 1.12 % CO and 0.23 % HCs for the combined fleet The recorded vehicle speeds varied from 34.5 mph to 83.5 mph with a mean of 56. 56 mph. Accelerations varied from -4.5 mph/sec to +4 mph/sec with a mean of 0.17 mph/sec. With a high emitter cut-point set at 4.0 % CO and 0.2 % HCs, 5.7% and 49.2% of the combined vehicle fleet were CO and HCs high emitters respectively. The instantaneous values of the exhaust CO and HCs emission concentrations exhibited a non-linear relationship with vehicle speeds and accelerations.

Using the PVEMP database, a real-time modal exhaust emission concentration model was developed. The model was based on the non-linear multivariate regression of the speed-acceleration matrix for modal-average CO and HCs exhaust emission concentrations aggregated by vehicle type. This model, the Purdue Vehicle Exhaust Emission Model, the Borman Expressway Application (PVEM-BEA), requires input of vehicle speeds and vehicle type for each passing vehicle at a given location within a short time interval. Then, it calculates the accelerations; the mode-average CO and HCs exhaust emission concentrations for each passing-vehicle, and the average values by class of vehicle within the time interval. It also calculates the vehicle flow rates, and makes decisions about the exhaust emission concentration levels by comparing the flow-average emission rates to designed threshold values.

The implementation of PVEM-BEA requires the use of advanced traffic monitoring systems such as the Autoscope1>4 for the acquisition of real-time traffic parameters. PVEM-BEA may be used as a stand-alone model running on a laptop PC or as integrated in the Borman Expressway traffic management center. The current version of PVEM-BEA requires a FORTRAN compiler.


exhaust emissions monitoring, exhaust emissions modeling, FTIR air monitoring system, construction zone safety, SPR-2176

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Performing Organization

Joint Transportation Research Program

Publisher Place

West Lafayette, IN

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