Analysis of methyl tert-butyl ether in the atmosphere and implications as an exclusive indicator of automobile exhaust

This study investigated the feasibility of using methyl tert-butyl ether (MTBE) as an unambiguous indicator for traffic emissions. The concept involves using ratios of volatile organic compounds (VOCs) to MTBE concentrations, which are characteristic of traffic emissions to reveal the excess concentration contributed by non-traffic sources. To execute this concept an analytical method based on gas chromatography/mass spectrometry was employed to measure various VOCs and MTBE simultaneously. Poor separation of MTBE and 2-methyl pentane caused by water in the samples was circumvented by selectively monitoring the characteristic ion peak (m/z=73) of MTBE. Air samples were collected during three periods and analyzed simultaneously for MTBE and other ozone precursors so that their ratios to MTBE could be examined. Two sample collections at different locations were made in an urban environment, in which high correlation in concentration was observed between most VOCs and MTBE for samples collected during hours of heavy traffic. The third collection was made near a cluster of petroleum refineries in order to compare VOCs/MTBE ratios from different VOC source regions. Ratios of ethene/MTBE, benzene/MTBE, toluene/MTBE, etc. obtained from the industrial site were significantly greater than those from the two roadside sites indicative of additional VOC sources other than internal combustion. Although rather constant values of VOCs/MTBE ratios were observed for most urban samples, the ratios noticeably shifted toward higher values in late night samples when the sources from traffic subsided and the effect of sinks prevailed.