A UV differential optical absorption spectrometer for the measurement of sulfur dioxide emissions from vehicles

Abstract

A differential optical absorption spectrometer for measurements of low-level sulfur dioxide (SO2) emissions from vehicles in real time was developed and employed. With a time resolution of 3 s and an optical path length of 19.6 m, a minimum detection limit of 75 ppbv SO2 (three times the standard deviation) was achieved. The wavelength region covered, UVB, was chosen to include the major SO2 absorption feature at 300 nm, while avoiding wavelength regions in which other components of vehicle exhaust are known to absorb. However, formaldehyde was found to be present in vehicle exhaust in high enough concentrations to be a major interferent. The analysis software was modified to account for the formaldehyde interferent using a two-dimensional fitting routine. The application of the instrument to real vehicle exhaust demonstrated that it was capable of measuring the contribution to SO2 emissions from lubricant oil sulfur over the range of current and future oil sulfur levels.