Publication Date


Document Type

Conference Proceeding

Organizational Units

Chemistry and Biochemistry


Atmospheric chemistry, Emissions, Pollutants


On-road emissions are precisely the emissions which are impacting the air quality and which need to be controlled if air quality improvements are desired. Remote sensing measures mass emissions of CO, HC, NO and smoke per kg (or per L) of fuel burned. On-road emissions are not certification emissions for new vehicles, although new vehicles measured on-road most often provide remote sensing readings well within their certification values. On-road emissions are not the same as readings from scheduled emission tests, although on average the two correlate very well. The major difference between scheduled emission tests and on-road emissions readings is how emissions variability is treated. All emissions tests show low variability when testing new, well controlled vehicles and show very high variability when testing older, and especially older broken, vehicles. Because on-road remote sensing readings can be obtained with a throughput of 10,000 vehicles per day, the variability of readings taken day after day on the same vehicle is readily apparent. By contrast, scheduled emission tests tend to be performed only once for vehicles which pass the first time (most vehicles) and are only repeated for vehicles which fail the first time. It has been shown from analysis of US data that many of the vehicles which subsequently receive passing readings do so because their emissions naturally vary and happen on the first test to be high and the second test low. Roadside tests in California carried out by their Bureau of Automotive Repair show that vehicles identified as on-road gross emitters by means of remote sensing and pulled over immediately by a policeman have an 83-88% (depending on the pollutant) chance of failing a California emissions test performed on the spot. On road emissions measured in Asia show large geographic variability and everywhere that a few vehicles are responsible for most of the on-road emissions.

Publication Statement

Paper presented at the Better Air Quality Workshop. Held in , Agra, India, 2004. Copyright held by the author, published by Better Air Quality 2004. User is responsible for all copyright compliance.

Rights Holder

Donald H. Stedman, Gary A. Bishop, Niranjan Vescio, Nitin Manawat, Peter McClintock


Received from author

File Format



English (eng)


11 pgs

File Size

106 KB