Multicomponent Remote Sensing of Vehicle Exhaust by Dispersive Absorption Spectroscopy. 1. Effect of Fuel Type and Catalyst Performance

Abstract

A remote sensor incorporating UV and IR spectrometers in conjunction with an innovative optical design is described. The instrument was used to noninvasively measure over 20 pollutants in the exhaust of 19 in-use vehicles powered by a range of fuelsreformulated Phase II gasoline, diesel, compressed natural gas, and methanol blended with 15% gasoline. CO2, CO, aldehydes, and aliphatic and speciated aromatic hydrocarbons were identified along with NOx, determined as the sum of NO, NO2; N2O and HONO were also measured, although their levels were typically below the instrument's detection limit. NH3 levels in vehicle exhaust are reported for the first time on a car-by-car basis. The exhaust from gasoline- and methanol-powered cars was found to contain elevated levels of NH3, in some cases over 1000 ppm, despite near stoichiometric air-to-fuel ratios, and were often significantly higher than corresponding NO levels. Catalyst efficiency is discussed as a function of NH3 and NO concentrations in the exhaust of vehicles operating “cold” and “hot”. In some of the tested vehicles, the three-way catalysts showed high reduction activity but poor selectivity resulting in the formation of NH3 and possibly other nitrogen-containing products other than N2. These observations could have significant implications on the formation of ammonium nitrate aerosol and on the acid-neutralizing capacity of urban air masses.