Real-time Motor Vehicle Emissions Analysis
Despite improvements in fuels, engines and catalytic converters, emissions of volatile organic compounds (VOCs) from motor vehicles remain a significant source of pollution in urban areas, and under appropriate conditions result in the formation of photochemical smog. Selected Ion Flow Tube Mass Spectrometry (SIFT-MS) offers a unique ability to study motor vehicle emissions because it can analyze individual VOCs and certain inorganic gases (such as NO and NO2) in real-time, even at high humidity.
In this study, most compounds were quantified using multiple reagent ions, which allowed the best reagent ion — product ion combinations to be selected. By minimizing interferences, SIFT-MS maximizes selectivity and accuracy.
Table 1 provides a brief overview of two gasoline-powered vehicles that had emissions analyzed using a Syft Technologies Voice200 SIFT- MS instrument. Exhaust gases were diluted 50% with ambient air and drawn continuously through PVC tubing using a small battery- powered pump. The SIFT-MS instrument extracted only a fraction of this gas for analysis.
|Manufacturer and Model||Subaru Legacy||Nissan Murano|
|Identification in this report||Car A||Car B|
|Year of manufacture||2000||2005|
|Displacement (cubic centimeters)||2500||3500|
|Odometer reading in kilometers (miles)||131000 (82000)||22000 (14000)|
|Catalytic converter fitted||No||Yes|
|Time elapsed since previous use*||2 hrs||2 hrs|
|Engine RPM (at start and end of experiment)||1500||1500 – 1250|
* Apart from shifting the vehicle into the testing park space
Blanks were analyzed by pumping outdoor ambient air through the same length of tubing and were subtracted from the data presented here.
Figures 1 and 2 show the results of real-time analysis of the exhaust gases of the two vehicles. For clarity, the figures show different classes of compounds. These data were obtained for cars from a near-cold start, the engines at low revolutions and without load for the duration of the analysis. The engine of each car was maintained at consistent revolutions. The data reveal very different VOC profiles — both in terms of relative and absolute abundances, and in terms of temporal changes in the data.
The real-time, broad-spectrum, humidity-independent analysis provided by SIFT-MS makes it ideally suited to direct analysis of VOCs in motor vehicle tailpipe emissions. The Syft Voice200 SIFT- MS solution provides a robust, easy to operate package for sensitive, quantitative analysis over a wide dynamic range.
|Figure 1: Real-time concentrations of various oxygenated compounds in the exhaust gases emitted by (a) car A and (b) car B (see Table 2), determined using SIFT-MS.||Figure 2: Real-time concentrations of selected hydrocarbons and nitrogen- containing compounds in the exhaust gases emitted by (a) car A and (b) car B (see Table 2), determined using SIFT-MS.|