Hot Spot Analysis of Real World Vehicle Emissions Based upon a Portable On-board Measurement System

The purpose of this study is to investigate hot spots along roadways where high values of emissions are observed based upon real-world, on-road vehicle emissions measurements. A portable instrument, the OEM-2100 manufactured by Clean Air Technologies International, Inc., was used to measure on-road tailpipe emissions of carbon monoxide (CO), nitric oxide (NO), hydrocarbons (HC), and carbon dioxide (CO2) on approximately a second-by-second basis during actual driving. Engine parameters such as vehicle speed, engine rpm, engine coolant temperature, manifold absolute pressure (MAP), percent of wide open throttle, and open loop/closed loop flag were also recorded using the OEM-2100. This paper presents examples of the data collected and illustrates the results obtained from analysis of on-road measurements. A key insight is that hot spots can be determined by spatial analysis of real-world on-road vehicle emissions data. In some cases it was observed that ratio of emissions estimates at hot spots to average emissions observed during free-flow was as high as seven as in the case of CO emissions for one of the study corridors. This ratio was as high as five for NO and three for HC emissions. Some air toxics can be estimated as a percentage of HC emissions, therefore the spatial distribution of HC emissions is helpful to support exposure assessments. The relations between hot spots and possible explanatory variables are investigated. The on-road emissions measurement and analysis methods demonstrated in this work enable collection of real-world representative data that can be used to assist in design and management of traffic facilities, as well as for air quality monitoring, modeling, and planning purposes.