Spectroscopy applied to on-road mobile source emissions.

Not to be confused with emission spectroscopy, the detection of mobile source emissions by means of a remote sensing device (RSD) is almost entirely an application of absorption spectroscopy. In this article we discuss its application to the measurement of individual vehicle emissions remotely as the vehicle drives by in its normal driving mode. Most studies and commercial implementation have involved automobiles and light duty trucks.1–8* However, the same technology has been applied to heavyduty trucks,9 locomotives,10 snowmobiles,11 and airplanes in taxi and takeoff modes.12 The challenge in all these applications is to make precisely collocated absorption measurements at 100 Hz in both the ultraviolet (UV) and infrared (IR) regions of the spectrum with low noise. The ability to measure 1/1000