The Determination of Vehicle Emissions in Exhaust Gases and Ozone Precursors in Ambient Air with a Built-in Preconcentrator/GC System

Importance of the Topic

The accurate measurement of hydrocarbon emissions from internal combustion engines is essential for evaluating ozone formation potential and ensuring compliance with air quality regulations. Ozone precursors such as C2 to C12 hydrocarbons interact with nitrogen oxides under sunlight to form ground level ozone, a regulated pollutant.

Study Objectives and Overview

This work describes the development and validation of a custom gas chromatograph system equipped with an integrated preconcentration trap and dual flame ionization detectors. The aim is to quantify hydrocarbons ranging from C2 to C13 in vehicle exhaust and ambient air samples across a wide concentration span.

Instrumentation

• SCION 456 GC with built in sample preconcentration trap
• Nafion sample dryer for moisture removal
• Valco valve assembly directing sample to dual FIDs
• PLOT Al2O3/KCl column 50 m x 0.32 mm for C2 to C6 separation
• SCION 1 column 60 m x 0.32 mm for C6 to C13 separation

Methodology

Approximately 100 mL of gas sample is drawn through the dryer into a multi absorbent trap held at 0C. After sample loading and trap purge, the contents are desorbed at 220C and split between two capillary columns. A temperature program from 0C to 200C at 10C per minute with appropriate hold times ensures baseline resolution of target analytes. Dual FIDs record chromatograms for light hydrocarbons and heavier species separately.

Main Results and Discussion

Chromatograms for C2 to C6 and C6 to C13 hydrocarbons demonstrate clear peak separation for compounds including ethane, ethene, propane, benzene, toluene, xylenes and higher alkanes. Precision studies with nine replicates of a standard mixture show retention time RSD below 0.07 for all analytes and peak area RSD below 1.4, typically under 0.5. Recovery tests indicate quantitative capture up to C9, 97 percent at C10 and 86 percent at C11. Recovery declines to around 50 percent for C12.

Benefits and Practical Applications

The integrated preconcentration GC system offers robust quantitative analysis of a broad range of hydrocarbons in both tailpipe emissions and ambient air. High recovery and subpercent precision support confident compound identification and accurate concentration measurement. This setup supports regulatory monitoring and environmental research requirements.

Future Trends and Applications

Advances may include coupling the preconcentration GC with mass spectrometry for enhanced compound identification and quantification of unknown species. Development of more selective adsorbent materials and field deployable portable systems could enable real time monitoring of ozone precursor levels in urban environments.

Conclusion

The custom SCION analyser integrating a built in preconcentrator, dual capillary columns and dual FIDs demonstrates high sensitivity, precision and recovery across C2 to C13 hydrocarbons. It provides a reliable tool for quantitative analysis of vehicle exhaust and ambient air ozone precursors.

References

• SCION Instruments Application Note 456 Determination of Vehicle Emissions and Ozone Precursors
• United States Clean Air Act 1970